Abstract:
A fluid and elastomer device for isolating dynamic loading between members connected to the device, the fluid and elastomer device comprising: an inner member that defines a compliance chamber; an outer member that defines an outer housing chamber; an elastomeric element flexibly interconnecting said inner member relative to said outer member; a passageway located in the compliance chamber and flow connecting the compliance chamber with a primary working chamber; a secondary compliance member joined to the passageway in the compliance chamber; a volume compensator located in the housing chamber the volume compensator comprising spring means, piston member at one spring end and a diaphragm member that overlies the piston; a member located between the compliance and housing chambers, the member being moveable with the outer housing, the moveable member in combination with the diaphragm defining a compensator chamber; and a volume of working fluid in said chambers and passageway.

Description:
FIELD OF THE INVENTION 
     The invention relates to devices for controlling dynamic vibration, and more particularly the invention relates to a fluid and elastomer vibration control device having a volume compensator and means for providing secondary compliance stiffness that are separate and discrete. 
     BACKGROUND OF THE INVENTION 
     Fluid and elastomer apparatus, often referred to in the art as hydraulic mountings, isolators and dampers include a fluid which provides for a greater range of isolation and/or damping characteristics than may be achieved in mountings, isolators and dampers that incorporate an elastomer alone. The expanded isolation and/or damping that is achieved by a fluid and elastomer apparatus may be a result of an increase in damping or inertial forces. 
     Fluid and elastomer isolation apparatus may be either single acting where fluid is pumped in response to the dynamic movement of one or more isolator components in a first direction, or double acting where fluid is pumped in response to the dynamic displacement of one or more isolator components in first and second directions. 
     Prior art single acting isolation devices include a single means that compensates for both changes in fluid volume due to changes in isolator fluid temperature and/or pressure and also provides secondary compliance for changing the stiffness of the isolator for use in different applications. In prior art single acting isolators, the volume compensation means and means for changing the stiffness of the isolator is comprised of a single flexible diaphragm member. 
     In many instances such prior art single acting isolators provide effective volume compensation and secondary compliance. However, use of the diaphragm to achieve both volume compensation and secondary compliance has associated shortcomings. In operation, isolators undergo repetitive motion at high pressure, and over time the thin, flexible diaphragms wear out. Additionally, prior art isolators with a single element for producing the required volume compensation and changing the stiffness of the isolator cannot be tuned with the requisite precision or across a broad range of stiffness values. Isolator performance is improved by tuning the device to the suitable stiffness for a particular application. The isolators must be sufficiently flexible to rapidly compensate for static axial displacements in response to temperature buildup as well as dynamic movements, and to provide the appropriate fluid pressure. Stiff isolators that provide effective volume compensation are particularly difficult to provide using prior art systems and methods. 
     The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative fluid and elastomer isolator that provides effective volume compensation and is tunable with precision and across a broad range of stiffness values. Accordingly, a suitable alternative 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 fluid and elastomer device including an inner member; and an elastomeric element flexibly interconnecting said inner member relative to said outer member. The fluid and elastomer device includes a compliance chamber; a primary working chamber; a compensator chamber; and a passageway interconnecting the primary working chamber and the compliance chambers. A secondary compliance member is located in the compliance chamber; and a volume compensator defines a portion of the compensator chamber. The volume compensator is located in a housing chamber and is separate from the compliance member. 
     In the fluid and elastomer device of the present invention the volume compensator includes a piston and diaphragm and the compensator is substantially unaffected by dynamic loading of the device, thereby increasing the useful life of the diaphragm. The fluid and elastomer device includes a restriction plate that defines a portion of the primary working chamber. The restriction plate is movable with the outer member. 
     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 fluid and elastomer isolation device of the present invention mounted for use in an aircraft application; and 
     FIG. 2 is a longitudinal sectional view of the fluid and elastomer isolation device of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now turning to the drawing Figures wherein like parts are referred to by the same numbers in the several views, FIG. 1 shows fluid and elastomer device  10  of the present invention installed in an aircraft transmission support structure  200 . The aircraft may be a helicopter for example. FIG. 2 is a longitudinal section view of a fluid and elastomer device of the present invention. For clarity, as the description proceeds the invention  10  may be referred to as a “fluid and elastomer device”, a “fluid and elastomer apparatus”, “fluid and elastomer isolator” or an “isolator”. But it should be understood that these terms should not be interpreted as limiting the scope of the present invention and that the present invention may be used as a mount or to provide damping, in addition to its use for vibration isolation as described hereinafter. 
     The fluid and elastomer isolator  10  is useful for controlling and minimizing dynamic vibration transmitted between a vibrating member  100  and a support structure  101 . As shown in FIG. 1, end  11  of the isolator  10  is connected to the vibrating member  100  which in turn is attached to transmission housing  103 , and end  13  is attached to the substantially stationary member or airframe fuselage  104  through strut member  101 . Although the isolator is shown with end  11  connected to the vibrating member  100 , and end  13  attached to the substantially stationary airframe, in an alternate embodiment end  13  could be attached to the vibrating member and end  11  could be joined to the substantially stationary member. 
     As shown in FIG. 2 the isolator is a single acting tuned fluid and elastomer isolator. The fluid and elastomer isolator  10  comprises an inner housing member  12  that is substantially cylindrical and includes, closed end  14 , open end  16  and compliance chamber  18  formed therein between the open and closed ends. The closed end  14  includes a tubular attachment member  19  made integral with the closed end. The tubular member  19  is adapted to be connected to airframe strut  101  by a conventional means such as a bolt or rivet connection or the like. 
     A hollow cylindrical elastomer element  20  is conventionally bonded to the outer surface of the inner member  12  and is also preferably bonded to the inner surface of annular sleeve member  22 . The elastomer element may be made from any suitable material including natural rubber, blends of natural and synthetic rubber, silicone elastomer, or any other suitable flexible material. For isolator applications the elastomer is preferably lightly damped. 
     Outer housing member  24  substantially encloses and surrounds the inner housing member  12 , elastomeric element  20  and sleeve  22  and attaches to a vibrating member  100  such as a transmission, pylon or component thereof by clevis  105 . The elastomeric element  22  flexibly interconnects the inner housing member  12  relative to the outer member  24 . The outer housing member is unitary and includes first portion  26  that is substantially cylindrical, second portion  28  that is frustoconical and third portion  30  that is substantially cylindrical. The second portion  28  joins the first and second portions  26  and  30 . As shown in FIG. 2 the inner housing, elastomeric element and sleeve are substantially enclosed by the first housing portion  26 . 
     A primary fluid working chamber  29  is defined by the interior wall of the sleeve  22 , the face of restriction plate  60  adjacent to element  20 , and the face of the passageway  46  adjacent to plate  60 . The volume of the primary working chamber varies as the plate  60  moves toward and away from end  16  during operation of isolator  10 . 
     Volume compensator  50  is separate from the secondary compliance member  40  located in compliance chamber  18 . The compensator  50  includes a spring  52  that flexibly suspends piston  54  in cavity  32  formed in the outer housing member  24 . The spring shown in FIG. 2 is a coil spring although it should be understood that the spring could also be a conventional gas spring. The spring must have a sufficient axial length to displace piston  54  the distance required to compensate for changes in fluid volume. The spring is oriented along the axis of operation  34  with one spring end seated against closed housing chamber end  36  and the opposite end seated against hollow piston  54 . 
     The volume compensator also includes a rolling diaphragm  58  that overlies a portion of and is operative with the piston  54 . For purposes of describing the preferred embodiment of the invention the diaphragm may be made be made from a polyester fabric and nitrile elastomer. As shown in FIG. 2, the diaphragm includes a sidewall portion which is doubled over between the sides of the piston  54  and the walls of chamber  32 . The outer periphery of the diaphragm is held in place between restriction plate  60  and an annular shoulder  59  along the inner wall of the second chamber portion  28 . Volume compensator chamber  31  is defined by restriction plate  60  and diaphragm member  58 . In an alternate embodiment the diaphragm may be replaced in the volume compensator by a bellows or by sliding seals. 
     The piston  54  and diaphragm are displaceable in response to changes in fluid volume experienced during operation of isolator  10 . However unlike prior art single acting fluid and elastomer isolation devices, the volume compensator  50  does not undergo any dynamic loading. Therefore piston and diaphragm displacement is effected to compensate for changes in fluid volume produced by significant changes in operating temperature or other factors unrelated to dynamic loading of the fluid and elastomer isolator  10 . In this way, the diaphragm  58  will not wear out as frequently as with prior art single acting fluid and elastomer devices. 
     The restriction plate is threadably connected to the outer member  28  in a conventional manner, and by this connection the plate is fixed during operation of device  10 . As shown in FIG. 2, as assembled, a working gap  37  is provided between the restriction plate and end  16 . The restriction plate includes at least one restricted opening (not shown) that permits fluid  39  to pass through the plate between the compensation and primary working chambers when the fluid is under the requisite pressure. The lateral end of member  22  directed toward end  11  is butted against plate  60 . 
     Thus dynamic loading transmitted through the outer member causes the restriction plate and housing  24  to move as a single unit relative to the inner housing  12  toward and away from open end  16  and along axis of operation  34 . The restriction plate eliminates dynamic movement of the fluid by the volume compensator. Therefore the volume compensator has no significant effects on the dynamics of device  10 . 
     Secondary compliance member  40  is located in the compliance chamber  18  in working fluid  39  and is comprised of a cylindrical multi-layer member with alternating bonded elastomer members and metal shims  42  and  44 . The secondary compliance member is threadably connected to passageway  46 . The compliance member can be easily changed out or reconfigured with different material shims and/or elastomer members and in this way the stiffness of member  40  can be tuned easily and efficiently. It should be understood that other geometries such as a rolling diaphragm or a bellows could be used as the secondary compliance element  40  however the multi-layer member is illustrated for purposes of describing the preferred embodiment of the invention. The secondary compliance element is used to tune the isolator to improve performance of the isolator. By incorporating a separate volume compensator  50  and secondary compliance element  40  the fluid and elastomer isolator  10  of the present invention provides greater flexibility and precision when defining the stiffness of the secondary compliance member. 
     The passageway  46  is made integral with the secondary compliance element and is located in the compliance chamber  18 . The passageway is preferably an inertia track that has a helical shape which provides for a relatively compact passageway of the required length. An inertia track is any passageway that has a tuned inertia, for example a fluid mass which resonates at a selected frequency within the passageway. The length and area of the inertia track is selected to tune to the resonant frequency of the fluid. 
     The working fluid  39  is contained in the passageway  46  and in the compliance, compensator and primary working chambers  18 ,  31  and  29  respectively. Preferable working fluids include silicone oils and perfluorinated fluids. In the case of the fluid and elastomer isolator  10 , preferable fluids are generally those that exhibit high density and low viscosity with viscosities on the order of 1-10 centistokes. 
     During operation of the aircraft, dynamic loading produced by the vibrating member  100  is transferred through the outer housing member  24 , resulting in displacement of housing and restriction plate  60  along axis  34 , and relative to housing  12 , toward and away from housing end  16 . As a result of movement of the housing  24  and plate  60  toward end  16 , fluid  39  is displaced from the primary working chamber  29  to the passageway  46  and primary vibration compliance is provided. A volume of the fluid in the passageway  46  is displaced into the compliance chamber  18 . The fluid is transferred toward the primary working chamber  29  as the plate  60  is translated away from end  16 . During operation of isolator  10 , the dynamic loading experienced by the volume compensator  50  is negligible. When volume compensation is required, the spring length is increased or decreased and as a result the piston and diaphragm are displaced along axis  34  in the direction required to increase or decrease the fluid pressure in the working chambers in response to changes in fluid volume. As the piston and diaphragm are displaced, fluid  39  is transferred through the one or more restricted openings in plate  60 . 
     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.