Patent Abstract:
A vibration isolation member comprising an inner member comprising an outer periphery having a first dimension; an outer member comprising a base and a shroud that extends away from the base, the shroud adapted to overlay the inner member, said shroud defining an inner periphery having a second dimension, the second dimension being less than the first dimension; and a resilient member constrained between the shroud and the inner member, whereby the vibration isolation member provides iso-elastic dynamic stiffness and an interference between the inner and outer members in the event of a failure of the resilient member.

Full Description:
FIELD OF THE INVENTION 
   The invention relates to a vibration isolation member and more particularly the invention relates to a vibration isolation member that provides substantially equal dynamic stiffness in radial and axial directions and comprises an outer member with an inner periphery, an inner member with an outer periphery and a resilient member joining the inner and outer members wherein the dimensions of the inner and outer peripheries provide for an interference therebetween in the event of a failure of the elastomer. 
   BACKGROUND OF THE INVENTION 
   Vibration isolation members are frequently used in aircraft interior applications to reduce the vibration and noise exposure to delicate and sensitive instrumentation and also to passengers in the aircraft cabin. In aircraft applications the vibration isolation members must provide the requisite vibration reduction with a minimum size and weight vibration isolation member. 
   One means for effectively reducing such exposure to noise and vibration is to use a vibration isolation member that has iso-elastic stiffness properties. A vibration member that is iso-elastic has equal stiffness in the axial and radial directions. Iso-elastic stiffness permits the vibration isolator to provide dependable performance in any orientation and maximize vibration reduction for a given installation. A vibration isolation member that does not provide such iso-elastic stiffness properties will transmit vibration more efficiently in one or more directions, compared to an iso-elastic vibration member having the same minimum stiffness. 
   Additionally, it is desirable to include a mount fail-safe feature that prevents the mount from separating in the event the mount fails under loading. Several prior art mounts provide fail safe features that function in a single axial direction however, such prior art mounts typically do not have two fail safe paths. Moreover, in vibration isolation members that comprise iso-elastic members, the members frequently do not have a fail-safe or interference path that is defined by the components that comprise the mount. Rather the fail-safe feature is produced by adding washers or other discrete mechanical members to the member. The additional components required to provide a fail safe feature in an iso-elastic vibration isolation member add weight and increase the volume required to house the member in the aircraft. 
   The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide a vibration isolator that provides iso-elastic stiffness in combination with fail safe feature and thereby solves one or more of the shortcomings of present isolation devices and methods. Accordingly, a suitable vibration isolation member is provided including features more fully disclosed hereinafter. 
   SUMMARY OF THE INVENTION 
   In one aspect of the present invention this is accomplished by providing a vibration isolation member that provides iso-elastic stiffness and at least one fail-safe feature. 
   More specifically the vibration isolation member of the present invention comprises an inner member comprising an outer periphery having a first dimension; an outer member comprising a base and a shroud that extends away from the base, the shroud adapted to overlay the inner member, said shroud defining an inner periphery having a second dimension, the second dimension being less than the first dimension; and a resilient member constrained between the shroud and the inner member, whereby the vibration isolation member provides iso-elastic stiffness and an interference between the inner and outer members in the event of a failure of the resilient member. 
   The inner member is unitary and is comprised of a stem and a seat where the seat includes a first surface, a second surface spaced from the first surface and a third surface that joins the first and second surfaces. The third surface is oriented at an angle relative to the first surface. The seat has a frustoconical configuration. 
   The outer member shroud may comprise a single segment or may comprise a first segment, a second segment and a third segment, the second segment joining the first and third segments. The outer member first segment is oriented substantially axially, the third segment is oriented substantially radially and the second segment is oriented at an angle relative to the first and second segments. The third surface of the seat is substantially parallel to the second segment of the shroud. 
   The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of the vibration isolation member of the present invention. 
       FIG. 2  is a top view of the vibration isolation member of  FIG. 1 . 
       FIG. 3  is a longitudinal sectional view taken along line  3 - 3  of  FIG. 2 . 
       FIG. 4  is a longitudinal sectional view like the sectional view of  FIG. 3  illustrating a second embodiment vibration isolation member of the present invention. 
       FIG. 5  is a longitudinal sectional view like the sectional view of  FIG. 3  illustrating third embodiment vibration isolation member of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Turning to the drawing Figures wherein like parts are referred to by the same numbers in the Figures, the first embodiment vibration isolation member  10  of the present invention is disclosed in  FIGS. 1 ,  2  and  3 . 
   Generally, vibration isolation member  10  comprises an inner member  12 , an outer member  14  and a resilient member  16  that joins the inner and outer members. The resilient member is constrained between the inner and outer members. The inner and outer members  12  and  14  are relatively rigid. The vibration isolation member  10  is made from a conventional molding process well known to those skilled in the art and during the molding process the resilient member is bonded to the inner and outer members. The resilient member  16  may be comprised of any suitable material however for purposes of the preferred embodiment of the invention the resilient member is comprised of a silicone or a synthetic rubber. 
   As shown in the sectional view of  FIG. 3 , the isolator is adapted to be connected between a support structure  18  such as an aircraft frame for example, and a suspended body  20  which may be an interior aircraft instrument or trim panel. The isolator  10  of the present invention reduces the transmission of vibratory disturbances, which may be in the form of acoustic noise, between the support structure  18  and the suspended body  20 . The isolator also limits heat transfer between body  20  and structure  18 . Also shown in  FIG. 3 , the isolation member is joined to the suspended body  20  by conventional fastener  22  that extends between the body  20  and inner member  12 ; and is joined to the support structure  18  by fasteners  24   a ,  24   b  that extend through the outer member  14 . The fasteners may be comprised of any suitable fastener well known to those skilled in the art including, but not limited to screws or quick-connect fasteners. By these connections, the outer member  14  remains substantially stationary during use and the inner member  12  may be displaced in radial and axial directions represented by respective directional arrows  25  and  26 . 
   The relatively rigid inner member  12  is unitary and comprises an axially extending cylindrical stem  30  and frustoconical seat  32 . As shown in  FIG. 3 , the seat includes first and second faces  34  and  36  joined by angled surface  38  that extends outwardly from face  34  to face  36 . The surface  38  may extend at any suitable angle, Θ relative to face  34 . For purposes of describing the preferred embodiment of the invention, the angle may be about 55°. The stem is made integral with the seat  32  at face  34  and the free end of the stem extends outwardly from the opening in the outer member  14  defined by inner periphery  62 . Faces  34  and  36  are circular, planar members that join the surface  38  at respective outer edges. The inner member includes an axially extending bore  40  that extends through the stem and seat and is adapted to receive fastener  22  previously described above. The seat defines an outer periphery  42  that comprises a diameter, D′. The extent of the inner member outer periphery  42  is also represented in dashed font in  FIG. 2 . As shown in  FIG. 3 , when the member  10  is installed the seat is located proximate the support member  18 . Additionally, as shown in  FIG. 3 , the surface  36  is located a distance away from the support structure  18  to allow for displacement of inner member  12  when the isolation member  10  experiences a vibratory disturbance. 
   The relatively rigid outer member  14  is unitary and comprises a substantially planar flange or base  50  with bores  52   a  and  52   b  that are adapted to receive fasteners  24   a  and  24   b  as described hereinabove. The base  50  is made integral with an annular shroud  54  that overlays seat  32 . The shroud comprises a first segment  56  that extends in the axial direction defined by arrow  26 , a second segment  58  that extends substantially parallel to surface  38 , and a third segment  60  that extends in the radial direction defined by arrow  25 . The second segment  58  joins the first and third segments  56  and  60 . See  FIG. 3 . Although the second segment is shown at an orientation that is substantially parallel to surface  38  it should be understood that although such a parallel configuration is preferred the second segment could be oriented at any relative angle and do not have to be parallel. 
   Third segment  60  terminates at inner periphery  62  that defines diameter, D″. As shown in  FIGS. 2 and 3 , the outer periphery  42  has a diameter D′ that has a greater radial dimension than inner periphery  62  diameter, D″. In the event that resilient section fails, and the seat is displaced axially toward panel  20 , an interference or fail-safe load path would be created between the seat and the segment  60  preventing further displacement of seat outward from the outer member. Thus the inner member would be captured by the outer member. As shown most clearly in the sectional view of  FIG. 3 , to ensure that the desired interference is produced between the seat and shroud, the inner periphery  62  must terminate radially inwardly from the outer periphery  42 . 
   During molding, resilient member  16  is bonded to the surface  38  and also to the inner surface of second segment  58 . Additionally, the molding process produces relatively thin skin segments bonded along the inner surface of third segment  60  and inner periphery  62 , stem  30  and surface  34 , outer periphery  42  and along portions of the inner surfaces of flange  50  and first segment  56 . Apart from the skins, the main portion of the resilient member  16  has a substantially trapezoidal cross section. 
   The vibration isolation member  10  of the present invention provides iso-elastic stiffness. The term “iso-elastic” means that the isolation member  10  has substantially the same stiffness in the axial and radial directions for any applied load. Because the resilient member  16  is constrained between the inner member  12  and outer member  14  the resilient member  16  experiences combined shear loads and loads in either tension or compression regardless of the direction and magnitude of the load applied to the vibration isolation member  10 . 
   The vibration isolation member  10  of the present invention provides a double fail safe feature that captures the inner member and maintains it in the chamber  80  defined by the outer member and the support structure  18 . Failure of the elastomer member  16  or failure of the bonds between member  16  and either inner member  12  or outer member  14  will not permit the inner member to relocate outside of the outer member. The inner member is captured by either the structural panel  18  or by the interference between the seat and segment  60  as described hereinabove. Therefore, in order for the inner member seat to become displaced from the chamber  80 , failure of the inner member, outer member fasteners or structural member must occur in addition to the resilient member failure. Additionally, in the event the resilient member  16  fails the seat will not be displaced out of chamber  80 . The suspended body  20  will engage the rigid outer member while the seat will interfere with the inner member. Additionally, the structural member will impede additional axial displacement of the seat towards member  20 . In this way, the mount of the present invention provides double fail-safe feature in combination with its iso-elastic stiffness. 
   A second preferred embodiment vibration isolation member  70  is shown in  FIG. 4 . The alternate embodiment mount  70  includes relatively rigid inner member  72  comprises stem  30  and seat  32  which defines angled surface  38 . The stem  30 , seat  32  and surface  38  as well as the other components and features are the same as those described hereinabove in conjunction with first embodiment vibration isolation member  10 . In the second embodiment mount  70 , the stem  30  and seat  32  may be made directly integral. The inner member  72  does not include surface  34  joining the stem and seat. The second embodiment member  70  includes the double fail-safe feature and also includes an iso-elastic stiffness. 
   A third preferred embodiment vibration isolation member  75  is illustrated in  FIG. 5 . The alternate embodiment mount  75  includes relatively rigid outer member  76  with shroud  78 . As shown in  FIG. 5 , the shroud member is comprised of a hollow cone with a wall comprised of a single angled segment, that terminates at an inner periphery  62 . As described in conjunction with first embodiment isolation member  10 , the inner periphery  62  has a diameter D″ that is less than the diameter D′ of the outer periphery  42  of the seat  32 . The other components and features of member  75  are the same as those described hereinabove in conjunction with first embodiment vibration isolation member  10 . The third embodiment member  70  includes the double fail-safe feature and also includes an isoelastic stiffness. 
   It should be understood the use of outer member  76  and inner member  72  are not limited to the isolation members shown in their respective embodiments but rather, outer member  76  may be combined with inner member  72  if desired. 
   While I have illustrated and described a preferred embodiment of my invention, it is understood that this is capable of modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

Technology Classification (CPC): 5