Abstract:
A hollow elastomer shell with an apex end and a base end with the apex end and the base end having support surfaces thereon to provide compressive support and a pressure equalizer to maintain substantial pressure equalization between the interior of the elastomer shell and the exterior of the elastomer shell to prevent a fluid pressure differential between the interior of the hollow elastomer shell and the exterior of the hollow elastomer shell from prematurely limiting an elastomeric response of the shock isolator.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to shock isolators and, more specifically, to shock isolators that can provide compressive support while at the same time providing an extended range of operation through equalization of pressure inside and outside of the shock isolator.  
         CROSS REFERENCE TO RELATED APPLICATIONS  
         [0002]    None  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0003]    None  
         REFERENCE TO A MICROFICHE APPENDIX  
         [0004]    None  
         BACKGROUND OF T HE INVENTION  
         [0005]    Various elastomeric materials have been used, or suggested for use, to provide shock and/or vibration damping as stated in U.S. Pat. No. 5,766,720, which issued on Jun. 16, 1998 to Yamagisht, et al. These materials include natural rubbers and synthetic resins such as polyvinyl chlorides, polyurethane, polyamides polystyrenes, copolymerized polyvinyl chlorides, and poloyolefine synthetic rubbers as well as synthetic materials such as urethane, EPDM, styrene-butadiene rubbers, nitrites, isoprene, chloroprenes, propylene, and silicones. The particular type of elastomeric material is not critical but urethane material sold under the trademark Sorbothane® is currently employed. Suitable material is also sold by Aero E.A.R. Specialty Composites, as Isoloss VL. The registrant of the mark Sorbothane® for urethane material is the Hamiltion Kent Manufacturing Company (Registration No. 1,208,333), Kent, Ohio  44240 .  
           [0006]    Generally, the shape and configuration of elastomeric isolators have a significant effect on the shock and vibration attenuation characteristics of the elastomeric isolators. The elastomeric isolators employed in the prior art are commonly formed into geometric 3D shapes, such as spheres, squares, right circular cylinders, cones, rectangles and the like as illustrated in U.S. Pat. No. 5,776,720. These elastomeric isolators are typically attached to a housing to protect equipment within the housing from the effects of shock and vibration. The prior art elastomeric isolators are generally positioned to rely on an axial compression of the elastomeric material or on tension or shear of the elastomeric material. Generally, if the elastomeric isolator is positioned in the axial compressive mode the ability of the elastomeric isolator to attenuate shock and vibration is limited by the compressive characteristics of the material. On the other hand, in the axial compressive mode the elastomeric isolators can be used to provide static support to a housing, which allows a single elastomeric isolator to be placed beneath the housing to support the static weight of the housing.  
           [0007]    In general, if the elastomeric isolators are positioned in the shear or tension mode as opposed to an axial compression mode the elastomeric isolators provide better shock and vibration attenuating characteristics in response to dynamic forces due to shock and vibration. Unfortunately, elastomeric isolators, which operate in a shear or tension mode or in the axial compression mode, can generally not be placed beneath a housing to provide static support to the housing without substantially effecting the shock and vibration attenuation characteristics of the elastomeric isolators. Consequently, to provide static support for a housing, as well as effective shock and vibration attenuation characteristics the elastomeric isolators, which operate in the shear or tension mode, are generally placed along side or above a housing so that the elastomeric isolators can function in a shear or tension mode while tensionally supporting the static weight of the housing. The positioning in a shear or tension mode can require placing matching elastomeric isolators on each side of the housing. In one embodiment an elastomeric isolator provides compressive static support for a housing through shear resistance and in other embodiments the elastomer isolators provide compression resistance.  
           [0008]    One of the difficulties with shock isolators and particularly with elastomer shell isolators that function in the shear mode is that a fluid, which is maintained within a cavity of the shock isolator, can shorten the effective operating range of the isolator. That is, a shock isolator, which provides shear resistance to shock and vibration forces, begins to provide a non-shear response as the force on the shock isolator increases. This reduced effectiveness of the shock isolator is due to an increase of fluid pressure within the shock isolator. While increasing the pressure of fluid within a shock isolator has been used to increase the ability of a shock to support a compressive load, the present invention provides a contrary effect by incorporating a pressure equalizer in the shock isolator that allows the pressure of fluid inside and outside of the shock isolator to remain in equilibrium or in a near equilibrium condition thereby allowing the resistance to shock and vibration to be provided solely by the characteristics of the elastomer and the elastomer configuration.  
         SUMMARY OF THE INVENTION  
         [0009]    An elastomer shock isolator to support the static weight of a housing while at the same time effectively attenuating shock or vibration imparted to the housing with the shock isolator having a pressure equalizer for equalizing the fluid pressure inside and outside of the shock isolator to prevent the fluid pressure within the shock isolator from limiting the elastomeric operating range of the shock isolator.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is perspective view of a two-tetrahedron elastomer shock isolator;  
         [0011]    [0011]FIG. 2 is a partial sectional side view of the two-tetrahedron elastomer shock isolator of FIG. 1 with base end members secured to the ends of the shock isolator;  
         [0012]    [0012]FIG. 3 is a sectional view taken along lines  3 - 3  of FIG. 2;  
         [0013]    [0013]FIG. 4 is a front elevation view showing the two-tetrahedron elastomer shock isolator of FIG. 1 supporting the weight of a cabinet or housing;  
         [0014]    [0014]FIG. 4A is a cross sectional view of a two-tetrahedron elastomer shock isolator with a pressure equalizer located in a base member of the elastomer shock isolator;  
         [0015]    [0015]FIG. 5 is a cross sectional view of a two-tetrahedron elastomer shock isolator with pressure equalizer connected to the shock isolator; and  
         [0016]    [0016]FIG. 7 is a plot of the force versus displacement for a shock isolator having a pressure equalizer and a shock isolator without a pressure equalizer. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    [0017]FIG. 1 is a perspective view of a one-piece shock isolator  30  for providing shock and vibration attenuation while providing axially offset support to an object. Isolator  30  is a one-piece two-tetrahedron elastomer shock isolator  30  that simultaneously isolates shocks and supports a static load. Shock isolator  30  has a set of integral elastomer side walls forming a first tetrahedron elastomer shell  31  with a tetrahedron shaped cavity  31   c  therein and a second tetrahedron elastomer shell  32  having a set of integral elastomer side walls forming a second tetrahedron elastomer shell with a tetrahedron shaped cavity  32   c  therein. A central axis  33  is shown extending through an apex end  32   a  of elastomer shell  32  and an apex end  31   a  of elastomer shell  31 . FIG. 2 shows apex end  31   a  and apex end  32   a  are smoothly joined to each other at junction surface  39  to form the one-piece two-tetrahedron elastomer shock isolator.  
         [0018]    [0018]FIG. 1 shows the top tetrahedron elastomer shell  32  has a triangular shaped base end that forms a first support surface  32   b . Similarly, the bottom tetrahedron elastomer shell  31  has a triangular shaped base end that forms a second support surface  31   b . The conjunction of the apex ends of the two-tetrahedron elastomer shells provides an integral force transfer region between the triangular shaped base ends  31   b  and  32   b  of the two-tetrahedron elastomer shells  31  and  32 .  
         [0019]    In order to provide shear resistance the base ends  31   b  and  32   b  are laterally offset with respect to the conjoined area  35  (FIG. 3), which occurs at the conjunction of the apex ends of tetrahedron elastomer shells  31  and  32 . That is, a line parallel to axis  33  that extends through base end or first support surface  32   b  does not extend through the conjoined area  35  between the apex of the two-tetrahedron elastomers  31  and  32 . Similarly, a line parallel to axis  33  that extends through the second base end or support surface  31   b  does not extend through the conjoined area between the two apex ends  31   a  and  32   a  of the two-tetrahedron elastomers  31  and  32 . Consequently, forces applied to base ends produce shear within the elastomer. This type of elastomer shock isolator which functions in the shear mode is more fully shown and described in my copending application titled Double Triad Elastomer Mount Ser. No. 09/779,423 Filed Feb. 8, 2001 and is hereby incorporated herein by reference.  
         [0020]    [0020]FIG. 2 shows a partial side elevation view of two-tetrahedron shock isolator  30  with a section line  3 - 3  extending though the conjoined region  39  between the two-tetrahedron elastomer shells  31  and  32 . FIG. 2 illustrates the rotational location of the top tetrahedron elastomer  32  with respect to the bottom tetrahedron elastomer  31 . A rigid base member  37  is secured to base end  32   b  and likewise a rigid base member  38  is secured to base end  31   b . FIG. 4 shows the two-tetrahedron elastomer shock isolator  30  supporting the static weight of a housing  60 , which contains equipment to be protected from shock and vibration. Note, a single shock isolator  30  can provide unpaired support for the housing while at the same time provide the proper shock and vibration attenuation characteristics. Although a single shock isolator  30  is shown supporting an article, multiple shock isolators can be used to coactively support an article to be protected from shock and vibration.  
         [0021]    [0021]FIG. 3 shows a cross sectional view of the two tetrahedron shock isolator  30  showing the apex conjoined area  35  where forces are transferred between the apex ends of the two-tetrahedron elastomer shells  31  and  32 . For illustrative purposes the outline of the bottom support surface  31   b  is shown in dotted lines. As evident from FIG. 3 the conjoined region or area  35  is laterally offset from the outer triangular shaped area  31   b  that forms the bottom support for shock isolator  31 . In the embodiment shown a fluid passage  44  extends between the top tetrahedron elastomer shell  32  and the bottom tetrahedron elastomer shell  31  to allow flow of fluid between the cavities in each of the elastomer shells. The flow of fluid between cavities can be controlled by positioning an appropriate size orifice between the adjacent chambers or cavities.  
         [0022]    [0022]FIG. 4A shows a cross sectional view of the two-tetrahedron elastomer shock isolator  30  with a first rigid plate or base member  37  secured to the triangular shaped base end  32   b  of tetrahedron elastomer shell  32  and a second rigid plate  38  secured to the triangular shaped base end  31   b  of tetrahedron elastomer shell  31 .  
         [0023]    An elastomer wall  32   e  forms an elastomer shell that extends angularly upward form apex end  32   a  to engage base member at position  32   c . The triangular shaped base member  32  engages the base  37  and defines an inner boundary or inner periphery  32   c  of the support surface  32   b  of tetrahedron shock isolator  32 . The lateral distance of the conjoined region  39  from the inner periphery  32   c  of tetrahedron shock isolator  32  is denoted by “x” with the distance x equal to or greater than 0 to thereby provide a cantilever support. That is the lateral offset of the base end  32   b  from the apex end  32   a  prevents the elastomer sidewalls from acting in an axial compression mode. Instead the elastomer sidewalls provide compression support through an axial offset axis that allows the elastomer walls of each of the two-tetrahedron shock isolators to move circumferentially inwards and outwards in response to dynamic forces.  
         [0024]    Located in rigid base end  37  is a pressure equalizer comprises an opening  37   a  with the opening sufficiently large to vent fluid within the cavity  32   g  without the pressure of the fluid in the cavity substantially interfering with an elastomeric response of the shock isolator. Similarly, located in rigid base end  38  is a second pressure equalizer comprises an opening  38   a  sufficiently large to vent fluid within the cavity  31   g  without the pressure of the fluid in the cavity substantially interfering with an elastomeric response of the shock isolator. That is, when isolator  30  is compressed the volume of cavities  31   g  and  32   g  decreases, which normally would cause the pressure within the isolator to increase. Even if the fluid is compressible, such as air, the pressure increase results in an alteration of the dynamic response of the shock isolator. Through use of a pressure equalizer one can maintain the dynamic response of the shock isolator as a function of the elastomeric shear resistance to shock and vibration forces.  
         [0025]    Referring to FIG. 5 there is shown an identical shock isolator having elastomer sidewalls  32  and  31  forming elastomer shells. Instead of the pressure equalizer comprising a vent passage, the pressure equalizer comprises a valve  40  valve normally remains in a closed condition until a pressure in the cavities  31   g  and  32   g , which are connected by a fluid passage  44 , exceed a venting pressure whereupon the valve  40  opens to vent fluid from within the cavities  31   g  and  32   g . The venting of the fluid within the cavities prevents the fluid pressure within the cavities of the shock isolator from resisting the normal elastomeric response of the shock isolator. In addition by holding the venting till a trigger event occurs one could use the present invention to produce a solid air column support for a cabinet until the trigger event such as a rapid increase in pressure causes a relief valve to open which would then allow the elastomer to act without the solid air column support  
         [0026]    [0026]FIG. 6 shows a shock isolator comprising a single elastomer shell  40  having a first end  40   a  and a second end  40   b . A base member  51  is secured to end  40   a  of elastomer shell forming a cavity  40   s  therein. Similarly, a base member  53  is secured end  40   b  of elastomer shell  40 . A pressure equalizer  52 , comprising a pressure relief valve, is located in fluid communication between cavity  42   s  and an region external to cavity  42   s  so that when the elastomer shell  40  is compressed a fluid within the cavity  42   s  can escape from the cavity at sufficiently rapid rate so as to prevent the pressure of the fluid within the cavity  42   s  from limiting the elastomeric response of the elastomer shell  40 . If one desires to have only axially offset support first end  40   a  and second end  40   b  can be laterally offset from one another; however, if axial offset support is not desired first end  40   a  and second end  40   b  need not be laterally offset. In this condition the elastomer provides compression resistance to shock and vibration. Thus the pressure equalizer provides for controlling the fluid entering the cavity or leaving the cavity to change a dynamic shock or vibration characteristic of the elastomer mount.  
         [0027]    In order to illustrate the operation of the shock isolator with and without the pressure equalizer reference should be made to FIG. 7. FIG. 7 shows the force F on a shock isolator plotted along the vertical axis and the compressive displacement of the shock isolator plotted along the horizontal axis.  
         [0028]    The first curve  51 , which is identified by a solid line, illustrate the response of the shock isolator without a pressure equalizer which results in the fluid pressure in the cavities increasing as the shock isolator compress. Note, even though the force increases the operating range or displacement of the shock isolator is severely limited since the fluid pressure within the shock isolator acts to limit the compression of the shock isolator. This has the effect of shortening the operating range of the shock isolator to a distance denoted by d 1 . In other words, the shock isolator “bottoms out” even though the elastomer in the shock isolator could effectively handle greater forces.  
         [0029]    The second curve  52 , which is identified by a dashed line, illustrate the response of the shock isolator with a pressure equalizer which results in the fluid pressure in the cavities maintained in substantial equilibrium with the fluid pressure outside the shock isolator. Note, as the force increases, the displacement of the shock isolator continues until the elastomer limit is reached. That is, since there is substantial pressure equilibrium between the inside and the outside of the elastomer the fluid pressure within the shock isolator does not limit the compression action of the shock isolator. This has the effect of providing an extended operating range for the elastomer shock isolator. A further feature of the present invention is that it allows one to maintain the inherent elastomeric response of the isolator to be retained whether the elastomer is designed for an elastomer compression mode, an elastomer shear mode or both.  
         [0030]    The present invention also provides a method of making a shock isolator to simultaneously provide compression support and shock isolation by molding an elastomer into a shape of a hollow shell such as a tetrahedron  40  having an internal cavity  40   s  with an apex end  40   b  and a base end  40   a . By molding the elastomer such that the base end  40   a  and the apex end  40   b  of the elastomer shell are axially offset from each other one can produce a shock isolator that functions in the shear mode. One can secure base member  51  to the base end  40   a  of the elastomer shell  40  and base member  53  to the apex end  40   b  to provide an elastomer shock isolator wherein the resistance to shock and vibration is counterbalanced by shear forces within the elastomer shell.  
         [0031]    In order to prevent the elastomer shell  40  from losing its elastomer response characteristics due to increase of fluid pressure in cavity  40   s  a pressure equalizer  52  is connected to base member  51  to vent fluid into and out of cavity  40   s  at a rate sufficiently fast so that the pressure of the fluid in the cavity does not substantially interfere with an elastomeric response of the shock isolator.