Abstract:
The present invention provides an energy absorbing element ( 200 ) (EAE) useful for limiting forces transmitted to an object attached thereto, said element comprising a hollow extruded member provided with threads ( 230 ), having a helical cut ( 210 ) through the wall of said member, said helical cut and the extrusion axis of said member being coaxial, said member being adapted to undergo deformation when under strain, whereby the force-displacement curve of said spacer when under strain is of a predetermined form and wherein said element may be stretched or compress by a length depending upon the pitch of said helical cut such that forces transmitted to said object are limited.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to energy absorbing elements designed to limit accelerations, and, more specifically, to energy absorbing mounting hardware. 
       BACKGROUND OF THE INVENTION 
       [0002]    Generally bolts, nuts, and spacers are designed as rigid elements with no ‘give’ or flexibility. These elements are constructed of solid metal or plastic materials with care taken to fix their yield strength, but generally without regard to the stress-strain curve of the element. 
         [0003]    U.S. Pat. No. 6,274,211 discloses a deformable element for absorbing kinetic energy which is a plastic pipe section having interior surfaces at opposite ends thereof. The plastic pipe section initially deforms elastically under an applied axial force and, when a yield stress limit is exceeded by the applied axial force, the plastic pipe section deforms or collapses with an approximately equal deforming force over a work stroke until adopting a physically deformed shape in which the interior surfaces at the opposite ends contact each other. The device for absorbing kinetic energy is also described including several plastic pipe sections stacked in a column with an intermediate plate between each adjacent pair of pipe sections. The plastic pipe sections and engaged around a tubular round body for support and guidance. An inner screw bolt can also be provided for pre-tensioning the plastic pipe sections. 
         [0004]    JP 2002 227898 discloses enhancement of deformability function in horizontal and vertical directions of a base isolating damper used in combination with a base isolating device for carrying out base isolating support of a structure such as a building and a bridge. A steel pipe is used in a damper body, and an intermediate part between base parts of both ends in an axial direction of the steel pipe is cut to be a spiral shape, with the base parts being left, whereby a spiral part connected to the base parts is formed in the intermediate part between the base parts. 
         [0005]    JP 2001 289274 A discloses a spring made of a brittle material to be suitable for a part for a semiconductor manufacturing device incapable of using, for example, a metallic material, rationally and evenly manufacture through simple constitution, improve a yield, improve responsiveness to reduction of size and weight and a low load, and besides, remove a machined surface and the corner part of a spring body surface in a cracked state and a roughened surface state during machining and prevent the occurrence of breakage during application of a load or assembly, and provide a desired shape and size and to provide its manufacturing method. Non-metallic and heat resistant brittle materials are continuously disposed at given pitches in a direction extending coaxially with a load-applying direction and a spring body is provided to be expandable and contractible in the load applying direction. A cut groove in a spiral state is continuously formed in a cylinder pipe of the brittle material in the axial direction of a pipe. The cut groove 6 is caused to communicate with the internal part of the pipe to form a spring body. 
         [0006]    WO/2010/041235 discloses a method and apparatus for minimizing accelerations during impacts such as those encountered in motor vehicle accidents, helicopter and airplane crashes, explosions, and the like. The preferred embodiment takes the form of a helical spring-like member, designed to experience plastic deformation over a desired deformation length, under a given impact load threshold. The spring-like member is preferably installed in a mechanical linkage that is flattened under impact, straining the spring-like member in a predictable fashion. The operating characteristics of this system [namely the stress-strain curve, and thus the deformation length, impact load threshold, and acceptable load range for the system to be protected] can be easily controlled by varying the device dimensions and installation configuration. 
         [0007]    Equipment of combat vehicle can be protected from a rude shock (mine actuation, collision, shell hit). Equipment can be fixed to the vehicle by means of single-event energy absorbers. Hence, there is a long-felt and unmet need to provide energy absorbing mounting hardware of standard sizes (nuts, spacers, bolts) suitable to common practice without any special preparations or change in mounting methods. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    In order to understand the invention and to see how it may be implemented in practice, a plurality of embodiments is adapted to now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which 
           [0009]      FIG. 1  is a conceptual view of the combat vehicle provided with the energy absorbing elements; 
           [0010]      FIGS. 2   a - 2   c  is a conceptual view of the motor base mounted onto the carbody; 
           [0011]      FIGS. 3 to 7  are schematic views of the alternative embodiments of the energy absorbing spacers; 
           [0012]      FIG. 8  is a graph providing comparison of extension deformation force-travel curves for welded and non-welded samples; 
           [0013]      FIGS. 9-12  are schematic views of the alternative embodiments of the energy absorbing bolts and nuts; 
           [0014]      FIG. 13  is a conceptual view of energy absorbing spacers; 
           [0015]      FIGS. 14-15  are force-travel graphs of extension and compression deformations, respectively; 
           [0016]      FIG. 16  demonstrates tension distribution in the spacers of types A and B defined in  FIG. 13 ; 
           [0017]      FIG. 17  demonstrates tension distribution in the extended spacer. 
         SUMMARY OF THE INVENTION 
         [0018]    The invention discloses an energy absorbing spacer such as an internally-threaded nut. This device is largely cylindrical but is provided with a helical or spiral cut that changes the stress-strain characteristics of the device in a controllable and repeatable way. When subjected to strains such as vibrations, explosions, and the like, the device will compress or/and uncoil like a stretched spring, thereby transferring smaller forces between its connected elements. 
           [0019]    Another provision of the invention relates to attachment systems for chairs in vehicles. First of all any bolts, nuts, spacers and the like can be formed from the spiral elements referred to above. 
           [0020]    It is one object of the present invention to provide an energy absorbing element (EAE) useful for limiting forces transmitted to an object attached thereto, said element comprising a hollow extruded member provided with threads, having a helical cut through the wall of said member, said helical cut and the extrusion axis of said member being coaxial, said member being adapted to undergo deformation when under strain, whereby the force-displacement curve of said spacer when under strain is of a predetermined form and wherein said element may be stretched or compress by a length depending upon the pitch of said helical cut such that forces transmitted to said object are limited. 
           [0021]    It is another object of the present invention to provide the EAE as defined above, wherein said element is selected from the group consisting of a spacer, a bolt, a nut and any combination thereof. 
           [0022]    It is another object of the present invention to provide the EAE as defined above, wherein said extruded member comprises a cylinder. 
           [0023]    It is another object of the present invention to provide the EAE as defined above, where the plastic regime length of said force-displacement curve to the elastic regime length is within the range of about 4-70. 
           [0024]    It is another object of the present invention to provide the EAE as defined above, where the material of said member is chosen from a group consisting of metal, carbon fiber, composite material, plastic and elastomer. 
           [0025]    It is another object of the present invention to provide the EAE as defined above, where the cross section of said member is selected from a group consisting of: rectangular, square, ellipsoidal, triangular, and circular. 
           [0026]    It is another object of the present invention to provide the EAE as defined above, where said threads are located on the inner surface of said extruded member. 
           [0027]    It is still an object of the present invention to provide the EAE as defined above, where said threads are located on the outer surface of said extruded member. 
           [0028]    It is lastly an object of the present invention to provide the EAE as defined above, further provided with strain relief provision at the ends of said helical cut selected from a group consisting of: boring holes at the ends of said helical cut, and adding additional revolutions of increased stiffness at the ends of said helical cut. 
           [0029]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0030]    Military vehicles are exposed to various threats. IED&#39;s (Improvised Explosive Devices), shaped charges and etc. are known to impose significant effects to the crew and equipment inside the vehicle. Armored vehicles may successfully survive a blast and remain intact, within certain boundaries defined by the magnitude of accelerations experienced and construction of the vehicle. An explosion transfers large amounts of kinetic energy transferred through the vehicle&#39;s body due to the impact. That energy may deform the vehicle&#39;s walls rapidly, projecting dangerous shockwaves through the wall and beyond. 
         [0031]    Civilian vehicles are likewise exposed to dangerously high accelerations on impacts during collisions and other road accidents. 
         [0032]    In either case, the vehicle&#39;s walls are commonly used for mounting seats, boxes, electricity components, and other equipment. The mounting and attachments systems often rely on common threaded nuts and corresponding bolts. Bolts often are screwed in to threads drilled directly into the walls, or into welded “spacers” (which are often elongated nuts with internal threads). 
         [0033]    Impacts and other accelerations may cause any object mounted to the walls to detach from the fixtures (tearing the threads, the nut, the bolt, or other attachment device such as welds). Any objects attached by such means may then be thrown about the passenger compartment, endangering seat occupants, crew, and equipment integrity. 
         [0034]    The solution provided in the present invention comprises a deformable mounting spacer instead of the common threaded spacer. In case of impact—the EA spacer can deform and absorb impact energy, rather than transferring the entire shock to the mounted mass. 
         [0035]    The invention actually deals with the 3 most commonly used connection elements:
       1. Bolts.   2. Nuts.   3. Spacers.       
 
         [0039]    Spacers are designed for extension and compression and can be used for welding purposes and in add-on solutions. The welded spacers are preferably symmetric. The symmetric geometry provides more flexibility in the operation process. The proposed spacer is small and does not necessarily exceed the normal size of standard spacers. The welded spacers are designed for use in standard welding procedures and the add-on spacers can be configured into a hexagonal shape for use with standard tools (i.e. wrenches and etc.) 
         [0040]    Each spacer can be designed with a specific force-deflection curve to best suit a specific thread and mass. 
         [0041]    Nuts are designed for use in standard assembly methods. General look is very similar to a standard nut. The proposed nuts are suited to use in combination with standard bolts and of all known thread types. 
         [0042]    Bolts are designed for use in standard assembly methods. The proposed bolts have standard sizes. The proposed bolts are suited to use in combination with standard nuts of all thread types. In addition, the energy absorbing bolt can be modified from standard bolts to ease production. 
         [0043]    The situation during a side impact is shown in  FIG. 1 . A side impact detaches the mounting of an object  102  from the vehicle  103 . 
         [0044]    Reference is now made to  FIGS. 2   a  to  2   c , presenting technical solution wherein a motorbase  106  is mounted onto a car body  108  by means of an energy-absorbing spacer  200 . The proposed technical solution decreases potential traumatism causes by displacement of the motor during the traffic accident into a passenger compartment. 
         [0045]    The method can be especially effective when implemented in combination with large masses. Since the total energy of the crash is final, by absorbing the energy from the large masses we reduce the energy transferred to other parts in the vehicle compartment (i.e. crew compartment). 
         [0000]    
       
      
       E=W=F·X=m·a·X,  
      
     
         [0000]    where: E is energy of the collision, W is work, F is force, X is travel; m is mass and a—acceleration. 
         [0046]    Thus, if we connect the large masses with the proposed method, the more travel will result in more energy absorbed and not transferred to other parts in the vehicle. Amount of absorbed energy can be controlled by change in a number of the revolutions and shape thereof, 
         [0047]    In accordance with the current invention a peak load applied to the structure is reduced by means energy absorption by the proposed absorbing mounting hardware. 
         [0048]    The solution can be combined with no change to the current connection method and can be in parallel to any vibration control elements and etc. 
         [0049]    Reference is now made to  FIGS. 3 to 13  presenting alternative embodiments of energy-absorbing connection elements  200 . In accordance with the current invention, an energy-absorbing spacer  200  (or nut, bolt, or other element) shown in  FIG. 3  comprises two terminal tubular portions  204  and  206  interconnected by means of a helical portion cut through the wall of the spacer  200 . The inner threads  230  are provided for fixture of the spacer  200  to an object of interest (not shown. The helical portion forms a spring-like element that can be pulled apart quite some distance (for example twice its original length or more) before finally ripping. In some embodiments of the invention, a part of the tubular portions  204  and  206  are provided with the inner threads  230  to prevent a threaded bolt from interfering with the travel of the spiral section of the device during tension. During this travel, the stress-strain relation can be controlled, by means of the pitch and thickness of the cut, material of the spacer, thickness of the spacer walls, etc. Thus an exact stress-strain relation can be supplied by the device  200 , for instance allowing it to transmit a certain limited maximum acceleration for most of its travel. This limited acceleration might be for instance the maximum acceleration acceptable for civilian passengers, military personnel, infants, electrical boxes, different electronic devices and the like. 
         [0050]    In  FIG. 4  a cross-sectional view of an embodiment of an energy-absorbing spacer  200  is shown. The spacer  200  is fixed to the wall  240  by means of a weld  250 . The helical cut  210  is seen in the side of the device  200 , cutting entirely through the cylindrical walls of the spacer  200 . The female thread  230  of the spacer  200  allows a bolt (not shown) to be bolted into the spacer  200 . 
         [0051]    In  FIG. 5  a cross-sectional view of an embodiment of an energy-absorbing spacer  200   a  is shown. The spacer  200   a  is fixed to the wall  240  by means of a weld  250 . The spacer  200   a  includes a helical cut  210  in a outer portion  245 . A inner portion  235  is provided with female thread  230 . 
         [0052]    In  FIG. 6  a further embodiment of the device  200  is shown where a dedicated bolt  260  is fixed onto the vehicle wall  240  or other attachment surface by means of a weld  250 . The spacer  200  of the invention is then screwed onto this wall attachment bolt  260 , and thus the device to be attached (not shown) is bolted into the spacer  200 . The wall attachment bolt  260  may be of an easily-weldable material. Another reason for use of such a spacer is to avoid deformation of the energy absorbing spacer due to the heat of the welding process. It is also suitable when the use of a spacer which is manufactured from a non weld able material is required. 
         [0053]      FIG. 7  shows a further embodiment  200   b  of the invention wherein a wide flange  270  is provided on the wall side of the spacer  200   a  to facilitate welding or other attachment means. This may also reduce the heat transferred by the welding process to the energy absorbing member such that its properties are largely unaffected by the welding process. 
         [0054]    It is shown by experiments that there is no effect welding the spacer  200  to the wall  240  on energy absorbing properties thereof (see  FIG. 8 ). 
         [0055]      FIG. 9  shows an embodiment  200   c  of the invention where a male thread  280  is provided on a solid extension, and a female thread  230  is provided on the inner surface of the hollow part of the device  200   b.  Such an embodiment will be useful for cases where welding of the unit to a substrate is inadvisable or impossible. Such an element can also be used as a ‘plug-in’ retrofit to allow energy absorption characteristics to be introduced into existing mechanical systems, by simply placing such devices  200   b  between existing nuts and bolts (not shown) or other connection points. As will be obvious to one skilled in the art, the roles of female and male threads here exemplified may be reversed, and male-male or female-female versions may be produced as needed. 
         [0056]      FIG. 10  shows a variant of fixing an object of interest  300  for example, a device) to the wall  240 . A bolt  290  is turned into the energy-absorbing spacer  200   c  which is welded to the wall  240 . 
         [0057]      FIG. 11  presents an alternative embodiment  200   d  constituting an energy-absorbing bolt having a bolthead  310  and a threaded backend  320 . As seen in  FIG. 11 , the energy-absorbing bolt  200   d  and a nut  290  tie up articles  330  and  340 . 
         [0058]      FIG. 12  presents an alternative embodiment  200   e  constituting an energy-absorbing nut having an inner and outer portions  350  and  360 . The inner portion  350  is provided with the female thread  230  configured to receive a bolt  370 . The outer portion is configured to rest against an article to be tied up. In  FIG. 10   d , the articles  330  and  340  are tied up by the bolt  370  and the energy-absorbing nut  200   d.    
         [0059]    The energy absorbing element  200   a  shown in  FIG. 5  can also serve as an energy absorbing nut. 
         [0060]      FIG. 13  shows alternative embodiments  200  and  200   f  of the energy-absorbing spacer. Specifically, the energy-absorbing spacer  200   e  is provided with an internal wall  210   a  having a variable thickness. Variation in the wall thickness allows the threshold of actuation to be changed. 
         [0061]      FIGS. 14 and 15  present analysis-based force-travel graphs of extension and compression deformations, respectively. The obtained data indicate proportional dependence between threshold of actuation and thickness of the internal wall  210   a.    
         [0062]      FIGS. 16 and 17  demonstrate tension distribution in the spacers of types A and B defined in  FIG. 13 . 
         [0063]    Certain addition embodiments can be achieved by the following means:
       A shortened-length spacer can be achieved by cutting incomplete revolutions and/or by varying the pitch of the cut.   The energy absorbing spacer can be designed to meet any standard thread and weight requirement.   Unlike protection systems for human beings, acceleration thresholds may be less rigorous for equipment varieties. However, the minimum desired performance is such to prevent attached devices from detaching off the walls during a collision event of predetermined acceleration and duration.   Changes in geometric and material characteristics of the energy absorbing elements allow a specific operating threshold to be achieved. If acceleration applied to an object to be protected (electronic equipment and etc) overrides a predetermined value, the energy absorbing elements is actuated.   In a preferred embodiment, the dynamic reaction threshold (where plastic deformation starts) is designed to be slightly lower than the defined thread maximum shear strength. That way, the fixed mass will be held tight as long as the impact loads are lower than thread strength. Higher loads will force the slotted spacer to extend and absorb excess energy, thus preventing the thread/weld from tearing off the wall, and thereby securing the mass to within a distance limited by the spacer deformation length.       
 
         [0069]    Design advantages of seating systems incorporating the current invention include:
       Simplicity (a single energy-absorbing component is used with no internal structure or moving parts)   Low cost   Add-on solution for various seats and vehicles   Low weight   Bi-directional restraint (both compression and extension).   Multi-directional protection (both horizontal and vertical dampening possible).   Standard working tools are used—whether wrenches or standard welding machines.   Standard look and feel of bolts, nuts and spacers.       
 
         [0078]    Since the system is based on a single moving component, it is highly reliable and repeatable. Environmental conditions have no affect on the system behavior. Dust, mud, oil, etc. do not influence it. The system will always react as planned and as manufactured. Other shock absorbing systems that involve the interactions between two or more parts generally are affected by frictional or viscous forces and are thus inevitably affected by environmental conditions such as temperature and infiltration of mud, sand, oil, high temperature gas, etc. that may clog, heat, or otherwise change the system before or during an explosion or other impact. 
         [0079]    The system of the current invention is based on one or more energy-absorbing spacers as described herein. 
         [0080]    When installed in various mechanisms as described herein, the device prevents rebound that occurs naturally in some other systems, since after extending, the helix or spiral member of the current invention opposes not only tension but also compression forces, thus preventing the mechanism from bouncing back. Just as deforming the member from initial to fully-extended configuration absorbs energy and limits the transmitted acceleration, deforming the member on rebound will likewise absorb energy and limit the transmitted rebound accelerations. The spiral member of the invention can repeat this scenario numerous times. 
         [0081]    It is within provision of the current invention to convert hazardous impact energy into a plastic deformation of a solid component, which is designed to react within a predefined impact load threshold. 
         [0082]    It is within provision of the invention to provide a safe range of motion, to allow the objects attached by means of the energy absorbing spacer to experience accelerations independent of the vehicle frame accelerations. 
         [0083]    It is within provision of one embodiment of the current invention to dampen horizontal or vertical accelerations, restricting accelerations transferred to the device secured by the energy absorbing spacer to within safe limits. 
         [0084]    It is within provision of an embodiment of the current invention to provide an absorption component that can be installed for mainly vertical or horizontal impacts, such as those experienced in mine explosions or head-on collisions. 
         [0085]    The proposed technical solution provides energy absorbing mounting hardware of standard sizes (nuts, spacers, bolts) suitable to common practice without any special preparations or change in mounting methods. The conventional mounting hardware can be replaced be energy absorbing mounting hardware without any special preparations or change of mounting methods.