Patent Publication Number: US-6217011-B1

Title: Fluid mount including a partitionless compensator

Description:
RELATED APPLICATIONS 
     This application is a continuation of commonly-assigned U.S. patent application Ser. No. 08/905,368, filed on Aug. 4, 1997 now U.S. Pat. No. 6,032,936. 
    
    
     BACKGROUND OF THE INVENTION 
     Fluid or hydraulic mountings include a fluid which augments isolation and/or damping characteristics that may be achieved in elastomer mountings alone. This augmentation may take the form of adding additional damping or added inertial forces. Fluid mountings are generally described in LORD® Technical Article LL-2166 entitled “Understanding Hydraulic Mounts for Improved Vehicle Noise, Vibration and Ride Qualities” by W. C. Flower. Commonly assigned U.S. Pat. No. 4,811,919 to Jones describes a fluid mounting which incorporates a volume compensator. Other examples of fluid mountings and dampers may be found in commonly assigned U.S. Pat. Nos. 5,413,320 to Herbst, 5,374,039 to Schmidt et al., 5,127,607 to McGuire, and 5,197,692 to Jones et al., 5,540,549, to McGuire and 5,501,434 to McGuire. Fluid mountings are, in essence, tunable passive devices which use a fluid to add additional damping or tuned-fluid “inertia” effects. In all these devices, compensation of fluid expansion, pressurization, and fill to remove gas bubbles is a problem. However, prior art methods of accomplishing these feats have involved utilization of multi-component systems which tend to add unwanted cost and complexity. In particular, it is very important in aggressive fluid mounting applications, such as in fluid pylon isolators, that no gas bubbles are present in the operating chambers. In essence, relative movement between the inner and outer member will cause any bubble present to expand and contract instead of moving the fluid between the chambers. This degrades performance. Further, reliable methods of providing pressurization to minimize cavitation of the fluid at high relative motions is required. 
     Therefore, there is a recognized need for more effective and cost efficient methods of compensation, pressurization, and fill in fluid mounts. 
     SUMMARY OF THE INVENTION 
     Therefore, in light of the advantages and drawbacks of the prior art, the present invention is a fluid mounting adapted for attachment between a vibrating member and a structure for isolating or damping vibration therebetween. Accordingly, the present invention fluid mounting comprises a first and second operating chambers, a fluid passageway interconnecting the first and second operating chambers, a partitionless volume compensator including a compensator chamber separated into a gas-filled portion and a fluid-filled portion. The gas-filled portion overlies the fluid-filled portion and the chamber is devoid of any barrier separating the portions. At least one lock passage interconnects the fluid-filled portion with one of said first and second operating chambers. When operated in its upright orientation, any gas bubbles migrate upward through the lock passageway and into the gas-filled portion of the compensator, yet the fluid-filled portion is dynamically locked at the operating frequency of the mounting. 
     In another aspect, a bubble trap formed in a wall portion of one of said chambers focuses any bubbles present into said at least one lock passage. Preferably, the bubble trap is an annular groove formed by cooperation between a chamfer formed on a plug hole chamber and a chamfer formed on a plug received within said plug hole. In another aspect, a plurality of lock passages increase the speed at which bubbles enter the compensator chamber. In another aspect, an extension within the volume compensator extends part way into the compensator chamber and includes an opening cooperating with the lock passageway(s). The opening is always covered by the fluid regardless of an orientation of said mounting. This prevents air, once it leaves the operating chambers, from getting back in. In another aspect, the flexible element includes laminated construction which includes at least one rigid shim and at least two elastomer layers. Each of the at least two elastomer layers including a sloping end portion, one of which intersects with an end of said at least one rigid shim and another which intersects with an end of said inner member, thereby preventing gas bubbles from becoming trapped. This aids in fill of the mounting. 
     It is an advantage of the present invention that the partitionless compensator eliminates one or more components from the fluid mounting. 
     It is advantage of another aspect of the present invention that gas bubbles can be easily and quickly removed from the operating chambers during fill and during operation. 
     It is advantage of another aspect of the present invention that once the gas bubbles are removed, it is difficult for them to reenter the operating chambers. 
     The above-mentioned and further features, advantages and characteristics of the present invention will become apparent from the accompanying descriptions of the preferred embodiments and attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings which form a part of the specification, illustrate several key embodiments of the present invention. The drawings and description together, serve to filly explain the invention. In the drawings, 
     FIG  1   a  is a partial cross-sectioned side view of the present invention fluid mounting including partitionless compensator and bubble shedding features, 
     FIG. 1 b  is an enlarged partial cross-sectioned side view of one embodiment of a bubble trap, 
     FIG. 1 c  is an bottom view of the bubble trap along line c—c of FIG. 1 a , 
     FIG. 1 d  is an bottom view of a bubble shedding laminated elastomer section, and 
     FIG. 2 a ,  2   b  and  2   c  are cross-sectioned partial side views of another embodiment of the partitionless compensator shown in different orientations. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the Drawings where like numerals denote like elements, in FIG. 1 a , shown generally at  20 , is a first embodiment of the fluid mounting including a partitionless compensator  36 . The fluid mounting  20  is useful for controlling, and preferably minimizing, dynamic vibration (motion and/or force) transmitted between a vibrating member  21 , such as an helicopter transmission or the like, and a structure  23 , such as an aircraft fuselage, or the like. A detailed description of this type of mounting is found in U.S. Pat. No. 4,236,607. 
     The fluid mounting  20  comprises an elongated rigid inner member  22  adapted for interconnection to a first member  21 , such as a rigid structure, for example, a helicopter fuselage, and an outer member  24  adapted to be attached to a second member  23 , such as a vibrating element, for example, a helicopter transmission or pylon. A flexible elastomer element  26  flexibly supports the inner member  22  relative to the outer member  24 . Preferable materials include natural rubber, natural rubber and synthetic blends. Although, other suitable elastomers or flexible materials could also be used. As will be described later, the elastomer section may include laminated construction. 
     First  28  and second  30  operating chambers are formed within the mounting  20 , each of which preferably interacts with end portions of the flexible elastomer section  26 . A fluid passageway  32  which may include a tuned fluid inertia (resonant mass effect) interconnects the first and second operating chambers  28 ,  30 . This achieved by appropriate selection of the length and diameter of the passageway  32 . A fluid  34  is oscillated back and forth through passageway  32  as a result of dynamic vibrations between the inner member  22  and outer member  24 . 
     In a particularly novel feature, a partitionless volume compensator  36  attaches to a portion of the outer member  24 . The partitionless compensator  36  includes a compensator chamber  38  including a gas-filled portion  40  and a fluid-filled portion  42 . The gas-filled portion  40  overlies the fluid-filled portion  42  and the chamber  38  is devoid of any barrier separating the portions  40 ,  42 . Prior art compensators for fluid mounts include a flexible partition separating the various portions, for example, as is shown in U.S Pat. No. 4,811,919 to Jones. An additional example may be found in copending application 08/533,227 entitled “High Temperature Fluid Mount”. Removal of this diaphragm separation is key to the operation of one aspect of the present invention. 
     At least one lock passage  44  interconnects between the fluid-filled portion  42  of chamber  38  and one of the first and second operating chambers  28 ,  30 . The lock passage  44  is of the appropriate length and diameter such that flow is minimized at the predominant operating frequency of the mounting, i.e., the passage is locked. A fluid  34  such as silicone or perfluorinated polyether is contained within the first and second operating chambers  28 ,  30 , the fluid passageway  32 , the fluid-filled portion  42 , and the at least one lock passage  44 . 
     The viscosity of the fluid  34  is relevant to the operation of the invention. Notably, if the apparatus is an isolator a low viscosity (about 1-100 centistoke) fluid is needed, whereas if the device is a damper, a higher viscosity is desired (ex. 100-10000 centistoke). Preferably, the mounting also includes a bubble trap depression  46  formed in a wall portion  48  of one of said chambers  28 ,  30 . The bubble trap  46  is an irregularity formed in the surface which focuses any bubbles present into the at least one lock passage  44 . The surface leading to the bubble trap preferably includes a taper or incline. Notably, the bubble trap  46  is a depression at an even greater slope than the incline. This preferably dramatic change in slope catches any gas bubble and quickly diverts it through the lock passageway  44 . 
     In one embodiment, as best illustrated in FIG. 1 b , the bubble trap  46  is an annular groove formed into a wall portion of the first operating chamber  28 . The bubble trap  46  is preferably formed by cooperation between a chamfer  52  formed on a plug hole  50  interconnecting between the compensator chamber  38  and one of the operating chambers  28 ,  30  and a chamfer  52 ′ formed on a plug  54  received within said plug hole  50 . Together, the chamfers  52 ,  52 ′ form an annular groove. Notably, the shape of the groove could be varried. 
     In another aspect, it is preferable that the at least one lock passage  44  comprise a plurality of lock passages  44 ,  44 ′ to increase the speed at which bubbles may enter into the chamber  38 . For example, a bubble may enter through one lock passage  44  and the displaced fluid may exit through the other lock passage  44 ′. Even more lock passageways may be included if desired (See FIG. 1 c ). Preferably, the at least one lock passage  44  should exhibit a diameter greater than about 0.03 inch. More preferably, the at least one lock passage  44  exhibits a diameter between about 0.03 inch and 0.09 inch, and most preferably, a diameter of about 0.06 inch. Notably, it was discovered by the inventor that for sizes less than about 0.03 inches, bubbles do not pass easily into the chamber  38  and tend to get caught in the operating chamber  28 . Bubbles in the chambers  28 ,  30  may significantly degrade performance. Likewise, diameters above 0.09 inch tend to allow fluid  34  to oscillate through the lock passageway  44 . Preferably, a plurality of lock passages  44 ,  44 ′ interconnect between the compensator chamber  38  and an annular bubble trap  46  formed in a wall portion  48  of a highest one of said operating chambers  28 ,  30 . 
     The compensator chamber  38  should preferably be about half full of fluid  34 . A sight glass  55  is preferably mounted to a vertical wall portion  56  of said compensator chamber  38  enables viewing of the level of fluid  34  within the chamber  38 . A fill valve  58  provides means for pressurizing said gas-filled portion  40  thereby pressurizing the operating chambers  28 ,  30 . 
     Referring to FIG. 2 a - 2   c , in another aspect which prevents gas bubbles from getting into the chambers  28 ,  30 , an extension  56  projecting from a wall of the chamber  38  within the volume compensator  36  extends part way into the compensator chamber  38 . The extension  56  includes an opening  58  which is always covered by the fluid  34  regardless of the orientation of the mounting  20 . As shown in FIG. 2 a - 2   c , various orientations of the mount are illustrated, yet in each case, the fluid  34  within the fluid portion  42  covers the opening  58 . Since the opening is covered, no air can be reintroduced back into the operating chambers  28 ,  30 . In this embodiment, the fluid  34  level in the chamber  38  must be greater than one-half full, and preferably about two-thirds full. In a best mode, a plurality of lock passages  44 ,  44 ′ intersect with the opening  58 . Preferably, the extension  56  is formed on a plug  54 ′ which threads into said outer member  24 . 
     From the foregoing it should be understood that in an upright orientation, any bubbles formed or within the operating chambers  28 ,  30  will migrate upward into the bubble trap  46 , then into the at least one lock passage  44 , through said fluid portion  42 , and into said gas-filled portion  40 . The gas over fluid design improves on prior art designs in that any gas bubbles that are in the chambers  28 ,  30  can escape. 
     In another aspect illustrated in FIG. 1 d , means are incorporated to prevent air trapping within the chambers  28 ,  30  if the fluid mounting  20  includes a flexible element  26  having laminated construction. By the term laminated construction, what is meant is any flexible element  26  which includes a least one rigid shim  27  and at least two elastomer layers  29 . Each of the at least two elastomer layers  29  include a sloping conical end portion  31 , one of which preferably intersects with an end of the at least one rigid shim  27  and another which intersects with an end of said inner member  22 , thereby preventing gas bubbles from becoming trapped. Preferably, the sloping end portions  31  are angled at an angle theta • of at least 3 degrees from a horizontal plane. Preferably, the at least one rigid shim  27  is tubularshaped and includes an inner and outer diameter. The sloping end portion  31  preferably intersects the end of the at least one rigid shim  27  at its inner diameter. Notably, the mold would only locate the shim on this inner diameter. This provides support during bonding and allows the appropriate sloped contour. 
     While various embodiments, including the preferred embodiment of the present invention has been described in detail, various modifications, alterations, changes and adaptations to the aforementioned may be made without departing from the spirit and scope of the present invention defined in the appended claims. It is intended that all such modifications, alterations and changes be considered part of the present invention.