Abstract:
A pylon mounting system with vibration isolation is provided. The system generally includes a housing that defines a first fluid chamber and a second fluid chamber, a fluid disposed within the fluid chambers; a piston assembly at least partially disposed within the housing, and a tuning passage defined by the piston assembly for providing fluid communication between the fluid chambers. The piston assembly has a first arm and a second arm, and each arm has a tubeform bearing for providing pitch and roll stiffness.

Description:
TECHNICAL FIELD 
     The present application relates in general to heaver-than-air aircraft. More specifically, the present application relates to a pylon mounting system with vibration isolation. 
     DESCRIPTION OF THE PRIOR ART 
     One important engineering objective during the design of an aircraft is to minimize the weight and number of parts. It is especially important in the design and manufacture of helicopters and other rotary wing aircraft, such as tilt rotor aircraft, which are required to hover against the dead weight of the aircraft, and which are, thus, somewhat constrained in their payload in comparison with fixed-wing aircraft. 
     Methods and devices for isolating a vibrating body from another body are useful in a variety of technical fields and applications. Such isolators are particularly useful for isolating an aircraft frame from mechanical vibrations, which may be caused by other aircraft components. For example, the engine and transmission often generate unwanted vibrations that can be isolated from the aircraft frame by an isolator, such as a liquid inertia vibration elimination (LIVE) system. However, vibration isolators also add weight and complexity to an aircraft. Accordingly, the design and use of vibration isolators continues to present significant challenges to engineers and manufacturers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic and novel of a pylon mounting system according to this specification are set forth in the appended claims. However, the system, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a pylon mounting system according to one embodiment of the present specification; 
         FIG. 2  is a cross-sectional view of a vibration isolator according to one embodiment of the present specification; 
         FIG. 3  is a cross-sectional view of a vibration isolator according to another embodiment of the present specification; and 
         FIG. 4  is a cross-sectional view of a vibration isolator according to a third embodiment of the present specification 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the novel system are described below. In the interest of clarity, not all features of such embodiments may be described. It should be appreciated that in the development of any such system, numerous implementation-specific decisions must be made to achieve specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it should be appreciated that such decisions might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this specification. 
     Reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the system is depicted in the attached drawings. However, as should be recognized by those skilled in the art, the elements, members, components, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the example embodiments described herein may be oriented in any desired direction. 
     Referring to the appended drawings,  FIG. 1  is a perspective view of one embodiment of a rotor pylon  100  according to the present specification, which may be used to mount a rotor assembly to an aircraft. A transmission  105  transmits power from a power plant  110 , such as a jet turbine engine, to a rotor assembly (not shown) to provide lift and propulsion for the aircraft. Transmission  105  is connected to pylons  115  and  120 , which extend upwardly from roof beams  125  and  130 . Vibrations isolators may be provided to minimize the transfer of vibrations from the transmission  105  and other components to the rest of the aircraft. In the embodiment illustrated in  FIG. 1 , vibration isolators  135  and  140  according to the present specification are connected between transmission  105  and pylons  115  and  120 , respectively. 
       FIG. 2  is a cross-sectional view of an embodiment of a vibration isolator  200  according to the present specification. Vibration isolator  200  comprises an upper housing  205  and a lower housing  210 . A piston  215  is at least partially disposed within the interior of upper housing  205  and lower housing  210 . Piston  215  includes arms  216   a  and  216   b . Arms  216   a  and  216   b  have a conical profile in  FIG. 2 , but other profiles, such as a cylindrical profile, may be acceptable or preferable in other embodiments. Tubeform bearings  217   a  and  217   b  are bonded to arms  216   a  and  216   b , respectively, and may include casing  218   a  and  218   b . Bearings  217   a  and  217   b  are preferably high-capacity laminate (HCL) elastomeric bearings. The casings  218   a  and  218   b  may be open-ended or closed. Shims  219   a  and  219   b  may also be disposed between bearings  217   a  and  217   b , respectively, as needed for proper orientation. An upper elastomeric member  220  seals and resiliently locates piston  215  within the interior of upper housing  205 . Similarly, a lower elastomeric member  225  seals and resiliently locates piston  215  within the interior of lower housing  210 . Elastomeric members  220  and  225  may function as a spring to permit piston  215  to move or oscillate relative to upper housing  205  and lower housing  210 . When no load is applied, elastomeric members  220  and  225  are configured to locate piston  215  generally central to upper housing  205  and lower housing  210 . The interior of piston  215  defines a generally elongated tuning passage  230 . An upper fluid chamber  235  is generally defined by the interior of upper housing  205 , piston  215 , and upper elastomeric member  220 . Similarly, a lower fluid chamber  240  is generally defined by the interior of lower housing  210 , piston  215 , and lower elastomeric member  225 . 
     Tuning passage  230  extends centrally through a longitudinal axis of piston  215 , so that upper fluid chamber  235  and lower fluid chamber  240  are in fluid communication. A tuning fluid  245  is disposed in upper fluid chamber  235 , lower fluid chamber  240 , and tuning passage  230 . Tuning fluid  245  preferably has low viscosity, relatively high density, and non-corrosive properties. For example, tuning fluid  245  may be mercury or a proprietary fluid, such as SPF I manufactured by LORD CORPORATION. Other embodiments may incorporate hydraulic fluid having suspended dense particulate matter. 
     In operation, piston  215  is typically coupled to a vibrating body. For example, an aircraft transmission may be mounted to arms  216   a  and  216   b . Arms  216   a  and  216   b  may be oriented substantially perpendicular to the pitch axis, such that the torsional shearing of bearings  217   a  and  217   b  provide roll stiffness and the vertical stiffness of bearings  217   a  and  217   b  provide pitch stiffness without the need for additional pitch restraints. Upper housing  205  and lower housing  210  are typically coupled to a body to be isolated from vibration, such as a roof structure (not shown) of an aircraft. In such an arrangement, the aircraft structure is the body to be isolated from vibration, and the transmission is the vibrating body. Introduction of an axial force into piston  215 , such as from transmission vibrations, translates piston  215  axially relative to upper housing  205  and lower housing  210 . The movement of piston  215  forces tuning fluid  245  to move through tuning passage  230  in a direction opposite to the translation direction of piston  215 . Movement of tuning fluid  245  produces an inertial force that substantially reduces, or isolates, the force from piston  215  at a discrete frequency, i.e., the isolation frequency. 
       FIG. 3  is a cross-sectional view of another embodiment of a vibration isolator  300  according to the present specification. Vibration isolator  300  comprises an upper housing  305  and a lower housing  310 . A piston  315  is at least partially disposed within the interior of upper housing  305  and lower housing  310 . Piston  315  includes arms  316   a  and  316   b . Arms  316   a  and  316   b  have a conical profile in  FIG. 3 , but other profiles, such as a cylindrical profile, may be preferable in other embodiments. Arms  316   a  and  316   b  have a generally hollow interior. Tubeform bearings  317   a  and  317   b  are bonded to arms  316   a  and  316   b , respectively, and may include casing  318   a  and  318   b , which may cap arms  316   a  and  316   b , respectively. Bearings  317   a  and  317   b  are preferably high-capacity laminate (HCL) elastomeric bearings. Shims  319   a  and  319   b  may also be disposed between bearings  317   a  and  317   b , respectively, as needed for proper orientation. An upper elastomeric member  320  seals and resiliently locates piston  315  within the interior of upper housing  305 . Similarly, a lower elastomeric member  325  seals and resiliently locates piston  315  within the interior of lower housing  310 . Elastomeric members  320  and  325  may function as a spring to permit piston  315  to move or oscillate relative to upper housing  305  and lower housing  310 . When no load is applied, elastomeric members  320  and  325  are configured to locate piston  315  generally central to upper housing  305  and lower housing  310 . The interior of piston  315  defines a generally elongated tuning passage  330 . An upper fluid chamber  335  is generally defined by the interior of upper housing  305 , piston  315 , and upper elastomeric member  320 . Similarly, a lower fluid chamber  340  is generally defined by the interior of lower housing  310 , piston  315 , and lower elastomeric member  325 . 
     Tuning passage  330  extends centrally through a longitudinal axis of piston  315 , so that upper fluid chamber  335  and lower fluid chamber  340  are in fluid communication. A tuning fluid  345  is disposed in upper fluid chamber  335 , lower fluid chamber  340 , and tuning passage  330 . Tuning fluid  345  preferably has low viscosity, relatively high density, and non-corrosive properties. For example, tuning fluid  345  may be mercury or a proprietary fluid, such as SPF I manufactured by LORD CORPORATION. Other embodiments may incorporate hydraulic fluid having suspended dense particulate matter. 
     In operation, piston  315  is typically coupled to a vibrating body. For example, an aircraft transmission may be mounted to arms  316   a  and  316   b . Arms  316   a  and  316   b  may be oriented substantially perpendicular to the pitch axis, such that the torsional shearing of bearings  317   a  and  317   b  provide roll stiffness and the vertical stiffness of bearings  317   a  and  317   b  provide pitch stiffness without the need for additional pitch restraints. Upper housing  305  and lower housing  310  are typically coupled to a body to be isolated from vibration, such as a roof structure (not shown) of an aircraft. In such an arrangement, the aircraft structure is the body to be isolated from vibration, and the transmission is the vibrating body. Introduction of an axial force into piston  315 , such as from transmission vibrations, translates piston  315  axially relative to upper housing  305  and lower housing  310 . The movement of piston  315  forces tuning fluid  345  to move through tuning passage  330  in a direction opposite to the translation direction of piston  315 . Movement of tuning fluid  345  produces an inertial force that substantially reduces, or isolates, the force from piston  315  at a discrete frequency, i.e., the isolation frequency. 
       FIG. 4  is a cross-sectional view of yet another embodiment of a vibration isolator  400  according to the present specification. Vibration isolator  400  comprises an upper housing  405  and a lower housing  410 . A piston  415  is at least partially disposed within the interior of upper housing  405  and lower housing  410 . Piston  415  includes arms  416   a  and  416   b . Arms  416   a  and  416   b  have a conical profile in  FIG. 4 , but other profiles, such as a cylindrical profile, may be preferable in other embodiments. Arms  416   a  and  416   b  have a generally hollow interior. Tubeform bearings  417   a  and  417   b  are bonded to arms  416   a  and  416   b , respectively, and may include casing  418   a  and  418   b , which may cap arms  416   a  and  416   b , respectively. Bearings  417   a  and  417   b  are preferably high-capacity laminate (HCL) elastomeric bearings. Shims  419   a  and  419   b  may also be disposed between bearings  417   a  and  417   b , respectively, as needed for proper orientation. Additionally, a spherical elastomeric bearing  420  is bonded to piston  415 . An upper elastomeric member  425  seals and resiliently locates piston  415  within the interior of upper housing  405 . Similarly, a lower elastomeric member  430  seals and resiliently locates piston  415  within the interior of lower housing  410 . Elastomeric members  425  and  430  may function as a spring to permit piston  415  to move or oscillate relative to upper housing  405  and lower housing  410 . When no load is applied, elastomeric members  425  and  430  are configured to locate piston  415  generally central to upper housing  405  and lower housing  410 . The interior of piston  415  defines a generally elongated tuning passage  435 . An upper fluid chamber  440  is generally defined by the interior of upper housing  405 , piston  415 , and upper elastomeric member  425 . Similarly, a lower fluid chamber  445  is generally defined by the interior of lower housing  410 , piston  415 , and lower elastomeric member  430 . 
     Tuning passage  435  extends centrally through a longitudinal axis of piston  415 , so that upper fluid chamber  440  and lower fluid chamber  445  are in fluid communication. A tuning fluid  450  is disposed in upper fluid chamber  440 , lower fluid chamber  445 , and tuning passage  435 . Tuning fluid  450  preferably has low viscosity, relatively high density, and non-corrosive properties. For example, tuning fluid  450  may be mercury or a proprietary fluid, such as SPF I manufactured by LORD CORPORATION. Other embodiments may incorporate hydraulic fluid having suspended dense particulate matter. 
     In operation, piston  415  is typically coupled to a vibrating body. For example, an aircraft transmission may be mounted to arms  416   a  and  416   b . Arms  416   a  and  416   b  may be oriented substantially perpendicular to the pitch axis, such that the torsional shearing of bearings  417   a  and  417   b  provide roll stiffness. Spherical elastomeric bearing  420  and the vertical stiffness of bearings  417   a  and  417   b  provide pitch stiffness without the need for additional pitch restraints. Upper housing  405  and lower housing  410  are typically coupled to a body to be isolated from vibration, such as a roof structure (not shown) of an aircraft. In such an arrangement, the aircraft structure is the body to be isolated from vibration, and the transmission is the vibrating body. Introduction of an axial force into piston  415 , such as from transmission vibrations, translates piston  415  axially relative to upper housing  405  and lower housing  410 . The movement of piston  415  forces tuning fluid  450  to move through tuning passage  435  in a direction opposite to the translation direction of piston  415 . Movement of tuning fluid  450  produces an inertial force that substantially reduces, or isolates, the force from piston  415  at a discrete frequency, i.e., the isolation frequency. 
     Certain example embodiments have been shown in the drawings and described above, but variations in these embodiments will be apparent to those skilled in the art. The principles disclosed herein are readily applicable to a variety of mechanical systems, including many types of aircraft. The preceding description is for illustration purposes only, and the claims below should not be construed as limited to the specific embodiments shown and described.