Abstract:
An isolation mount for damping radial vibration as well as axial vibrations without attendant shear forces to the elastomeric medium. A toroidal casing has a plate extending through its radially outer wall and terminating with flanges on its radially inner edge near a cylindrical core of the casing. Elastomeric O-rings are disposed on either side of the plate so as to be captured between the respective flange and oppositely disposed casing wall. Relative movement between the plate and the casing then results in compressive loads to certain portions of one or both of the O-rings, regardless of whether the relative motion is in the axial or radial direction.

Description:
The invention herein described was made in the course of or under a contract, or a subcontract thereunder, with the United States Department of the Air Force. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to dampers and, more particularly, to vibration mounts of the elastomeric type. 
     Resilient mounting means are often used to isolate or dampen the vibration of operating machinery from other associated parts of machinery. Such is the case in an aircraft engine apparatus wherein it is desirable, for example, to mount an oil tank on the engine which is susceptible to vibration and which without isolation will produce fatigue cracks in the sheet metal skin of the tank. 
     One means of isolating such vibrational movement is to fasten an elastomeric material between the vibrating element and the element which is mounted thereto. Such an arrangement will provide adequate damping when the two elements are moving relatively toward each other (axially), since the elastic material will be in compression. However, when the two elements are moving away from each other there will be no damping provided. Further, when the two elements are moving transversely to each other (radially), then there is a damping action, but it tends to create a shear force on the elastic material which in time will finally cut and tear the material and render it useless. Various methods have been devised to provide compressive elastomeric damping for either axial direction, but in all such devices there is no provision for preventing the shear forces which occur from the radial vibrations. 
     It is, therefore, an object of the present invention to provide an isolation mount which dampens relative movement in either the axial or radial directions. 
     Another object of the present invention is the provision for an isolation damper which is effective in damping radial forces without attendant shear forces being imposed on the elastomeric medium. 
     Yet another object of the present invention is the provision for an isolation mount which is effective in use and economical and practical in design. 
     Another objective of the present invention is to provide a mount which limits deflection in both the radial and axial directions. 
     These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings. 
     Briefly, in accordance with one aspect of the invention, a toroidal casing which is adapted for attachment to an element for which damping is desired, is provided with a pair of axially spaced, elastomeric O-rings. A plate, which is attachable to the vibrating engine, extends radially inward through the casing wall and between the O-rings to a point surrounding but not touching the central core of the toroidal casing. The plate then flanges in opposite directions toward the ends of the toroidal casing to entrap the elastomeric O-rings between the flanges and the respective oppositely disposed casing walls. When the plate moves axially with respect to the casing, one of the two elastomeric O-rings is compressed between the plate and the casing end wall, while the other elastomeric O-ring is not affected. When the plate moves radially with respect to the casing, one side of each of the O-rings is compressed between the flanges and the radially outer walls of the casing, while the other half of the O-rings are not affected. In this way, the elastomeric O-rings are protected from shear forces which would otherwise tend to destroy them. 
     By another aspect of the present invention, the central core of the toroidal casing is of the predetermined length such that the O-rings are placed in a preloaded compression so as to establish positive connection between the casing and the plate. 
     By yet another aspect of the invention, the clearances between the flanges and the central core, and between the flanges and the casing end walls, are controlled to limit the mount deflections in the radial and axial directions, respectively. In the event of a mount overload, the plate flanges will come into contact with the casing and thereby limit further displacement to prevent overloading of the elastomer rings and prevent contact of the mounted part with adjacent objects. 
     In the drawings as hereinafter described, a preferred embodiment and modified embodiments are depicted; however, various other modifications and alternative constructions can be made thereto without departing from the true spirit and scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial longitudinal view of the isolation mount in the installed position in accordance with the preferred embodiment of the invention. 
     FIG. 2 is a perspective view of the mount in accordance with the preferred embodiment of the invention. 
     FIG. 3 is an end view thereof. 
     FIG. 4 is a sectional view of a modified embodiment of the present invention. 
     FIG. 5 is an end view thereof. 
     FIG. 6 is a sectional view of another modified embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, the invention is shown generally at 10 in the installed position intermediate the combustor casing 11 of an aircraft engine and a lube oil tank 12 supported thereby. Rigidly fastened to the combustor casing 11 by a pair of bolts 13 and 14 is a lower mount support 16 which has at its outer end a plurality of bolts 17 for rigidly securing the isolator plate 18 thereto. Since the combustor casing 11 in its normal operation is susceptible to both axial and radial (with respect to the core of the isolator) directed movements, these forces will be transmitted to the isolator plate 18 for damping by the elastomeric means within the isolator. Heretofore, effective damping was obtained in the axial direction, but in the radial direction, even though the forces were dampened, the shear forces which were created on the elastomeric material caused eventual failure. The present invention is designed to accommodate those radial vibrations without the creation of attendant shear forces. 
     The isolator plate 18 is resiliently connected to and forms a part of the isolator structure 19. Portions of the isolator 19 are rigidly connected to the lube oil tank 12 by way of a bolt 21, a bracket 22, and a flange 23 extending downwardly from the lube oil tank 12. 
     Referring now more specifically to the isolator itself as shown in FIGS. 2 and 3, that portion which is rigidly connected to the lube oil tank comprises a pair of axially spaced caps 24 and 26 interconnected by a central cylinder 27. The caps 24 and 26 have mutually parallel end walls 28 and 29 and cylindrical side walls 31 and 32, respectively, which terminate at opposed edges 33 and 34 to define an annular slot 36. Disposed in the slot 36 is the plate 18 in substantial alignment with the end walls 28 and 29, the inner edge 37 of the plate being spaced from the central cylinder 26 by a predetermined distance for reasons discussed hereinafter. Attached to the opposite sides of the plate 18, by welding or the like, are collars 38 and 39 which are L-shaped in cross section and which have flanges 41 and 42, respectively, extending parallel to but spaced from the central cylinder 27. Disposed between the collar 38 and the cap 24 is an elastomeric O-ring 43 which is held in place radially by the cylindrical side wall 31 and the flange 41, and axially by the end wall 28 and the collar 38. Similarly, an elastomeric O-ring 46 is captured between the cylindrical side wall 32, the flange 42, the end wall 29 and the collar 39. 
     The isolator 19 is constructed in such a manner that when in the free state, the elastomeric O-rings 43 and 46 are slightly compressed in both the axial and radial directions so as to provide a substantially tight connection between the plate 18 which is rigidly attached to the lower mount support 16, and the caps 24 and 26 which are rigidly attached to the lube oil tank 12 by the bolt 21 extending through the cylinder 27. When relative axial movement occurs between the plate 18 and the central cylinder 27, one of the elastomeric O-rings 43 or 46 is compressed while the other one is relaxed. If relative radial movement occurs between the two parts, a portion of the circumference of each of the O-rings is compressed while the remaining portion is unloaded. In neither case, nor in a combination of the two actions, do shearing forces act on either of the O-rings. 
     It will be recognized that during relative movement of the isolator parts in the radial direction, the flanges 41 and 42 move closer to the cylinder 27, and that during axial movement thereof, the edges of the flanges move toward one of the cap end walls 28 or 29. If the movement goes far enough, the parts will engage and further movement will be prevented. Thus, the free state spacing of these engageable parts may be predetermined and established so as to correlate with predetermined forces to thereby limit the amount of deflection in both the radial and axial directions and to limit the displacement of the relatively moving components when an overload occurs. Further, a total loss of mount integrity is prevented by the metal part contact in the event of failure of the elastomeric rings. 
     It should also be recognized that the spring rate and attenuation of the mount design can be varied as required by altering the cross-sectional shape of the O-rings, or stiffness of the elastomer material. Use of different cross section O-rings permits variation of the mount isolation characteristics for specific applications without the need for changes in other isolator parts. 
     Referring now to the alternate embodiment of FIGS. 4 and 5, the end caps 24 and 26 are rigidly secured by a pair of U-brackets 47 and 48 which are secured to the caps 24 and 26 by welding or the like and extend around the plate 18. The integral unit may then be rigidly attached to the bracket 22 by securing the cap 24 to the flange 23 by welding or the like, or by attaching one or both of the U-brackets 47 or 48 to the flange 23. The flanges projecting from the isolator plate 18 then take the form of a pair of posts 49 and 51 or a pair of small cylinders located centrally with respect to the cylindrical side walls 31 and 32. The elastomeric O-rings 43 and 46 are then entrapped radially by the post 49 and side wall 31 on the one side and by the post 51 and side wall 32 on the other side, and axially by the end wall 28 and plate 18 on one side and the end wall 29 and plate 18 on the other side. Movement in the axial direction is limited by the eventual engagement of the post ends 52 or 53 with the end caps 28 and 29, respectively, and is similarly limited in the radial direction to some extent by the possible engagement of the plate edges 54 and 56 with the U-brackets 47 and 48, respectively. It will be recognized, however, that for the radial movement, restraint is only provided in the plane of the brackets 47 and 48, and if it is necessary to limit movement in other directions on this radial plane, then it will be necessary to extend the brackets 47 and 48 in an arcuate manner around the side walls 31 and 32. However, for predicted vibration in a single radial direction, the present design would be sufficient. 
     In the modified embodiment of FIG. 6, the modified caps 57 and 58 are securely attached by a central cylinder 27 and have no side walls. The flanges 41 and 42 projecting outwardly on either side of the plate 18 are spaced radially outward from the plate inner edge 37 to form the outer boundary of the elastomeric O-rings 43 and 46. The inner boundary therefore is provided by the cylindrical walls of the central cylinder 27. Movement in the axial and radial directions is limited in the same way as in the preferred embodiment. 
     It will be understood that while the present invention has been described in terms of a preferred and modified embodiments, it may take on any number of other forms while remaining within the scope and intent of the invention. For example, the mount has been described in terms of use for mounting an oil tank; however, such a mount may also be used to attach an aircraft engine to an aircraft. Further, it will be recognized that the types of construction may take on various other forms. For example, the plate and collar combination may be made by simply joining two plates each having annular collars extending from one side thereof.