LAMINATED COMPOUND SUPPORT ELEMENT

Abstract: A sound isolating bearing has concentric inner and outer housings made of steel with a concentric shim between the inner and outer housings sandwiched by layers of a resilient elastomer. The longitudinal cross section of the shim is convex on both inside and outside surfaces with the same radius of curvature to allow cocking of the inner housing relative to the outer housing about a first point on the bearing axis midway between the ends and about a second pivot point outside the bearing in a plane midway between the bearing ends perpendicular to the bearing axis.

Description: The present invention relates to a laminated compound support element, referred to in the following as a laminated bearing, and more particularly to a laminated cylindrical sound isolation bearing capable of accommodating cocking about points internal as well as external to the bearing. Complex couplings utilizing laminated elastomeric technology typically have comprised a plurality of laminations differing in configuration and orientation and acting either independently or in combination with one another to handle each loading and motion. Such couplings are quite costly to manufacture and often run afoul of size restrictions. A preliminary novelty search uncovered U. S. Patent Nos. 1,868,818, 1,880,504, 3,071,422, 3,243,239, 3,504,902, 3,834,181, 3,862,812, 4,063,787, and 4,142,833. Laminated bearings find use in coupling systems, for example, in rotor blade retention systems suitable for use in aircraft such as helicopters. In conventional articulated rotor systems it is customary to provide a blade retention system for each axis of movement desired. For instance, in a fully articulated rotor system, three separate connections including precision roller bearings are provided for permitting pivotal movement of the blade about a lead-lag and flapping axis and for rotation about a pitch axis. Simultaneously, each of these connections must restrain movement of the blade against centrifugal forces imposed thereon during rotation of the rotation system. Such combinations of loads and motions result in early failure of these connections. In an effort to replace such complex structures, and alleviate many of the inherent disadvantages, attention has been directed to the use of elastomeric bearings comprising alternating and bonded layers of an elastomeric material and a substantially non-extensible material. The layers of the latter material are known as shims. Laminated bearings have the ability to carry high compressive loads normal to the layers (without excessive bulging of the elastomer), to accommodate deflection in torsion and/or shear along the layers and to accommodate motion. In the design of coupling systems in general which employ laminated bearings, numerous factors must be considered. Consideration must be given to fatigue life, weight and size limitations, structural interconnections, the desired spring rate of the bearing in various modes, and the motions and loads to be realized in the particular application. In complex couplings which must carry loading and accommodate motions about several different axes, as discussed above, the analysis of these considerations can be quite difficult. A computer is used. Finite element analysis determines a matrix of stresses and strains for the application and aids in the selection of the design control parameters of types and values for the application. Design control parameters include the geometry of the bearing (e.g. cylindrical, spherical, frusto-conical, and combinations thereof), the relative orientation of the layers, the size of the laminate and the characteristics of the elastomeric material. A support element in accordance with the preamble of claim 1 is disclosed by FP-A-974 123. This document discloses friction support systems and particularly bearings for rotating shafts. It is proposed, to interpose between at least one of the support elements and the mounting structure of this support element, a pad of resiliently deformable material having a greater thickness towards the boundaries of the friction area of said support element than in an intermediate zone. It is an object of the present invention to provide a laminated support element of simple design for a coupling system. Another object of the present invention is to provide a laminated bearing capable of carrying loading along a first axis and accommodating motion along a second axis and/or about a third axis. A further object of the present invention is to provide a support element having a generally cylindrical elastomeric laminate capable of accommodating cocking about points internal and external to the support element while carrying a load in a radial direction. These objects are solved by a support element according to claim 1. Preferred embodiments of the invention are subject matter of dependent claims 2 to 7. The features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawings in which: FIG. 1 is a perspective view of a cylindrical laminated bearing made in accordance with an embodiment of the present invention: FIG. 2 is a sectional view taken along longitudinal section II-II of FIG. 1; FIG. 3 is a sectional view similar to FIG. 2 except with the bearing being subject to cocking about Point A; FIG. 4 is a sectional view similar to FIG. 2 except with the bearing being subject to cocking about Point B; FIG. 5 is a perspective view of a shim made in accordance with an embodiment of the invention; FIG. 6 is an enlarged sectional view taken along section VI-VI of FIG. 5 showing a cross section of the shim; FIG. 7 is an enlarged sectional view showing the cross section of a shim made in accordance with another embodiment of the present invention; FIG. 8 is a sectional view of another embodiment of the invention showing a bearing incorporating a shim similar to that of FIG. 5 except radially split with elastomer therebetween: FIG. 9 is a sectional view of another embodiment of the invention showing a bearing similar to that of FIG. 8 except with an additional cylindrical shim. Referring to the drawings, FIG. 1 shows a perspective view of a bearing 10 made in accordance with an embodiment of the invention. The bearing 10 includes an inner housing 12 of a right circular cylindrical configuration, an outer housing 14 of a hollow right circular cylindrical configuration disposed concentric to and about the inner housing 12, and an elastomeric laminate 16 disposed and bonded therebetween. The laminate 16 comprises alternating layers 18 and 20 respectively of elastomeric and substantially non-extensible material therebetween bonded one to the other. The non-extensible layer 20 is called a shim. A single shim 20 is shown, but it should be understood that any number is within the purview of the invention. The shim 20 is of a hollow tubular configuration disposed concentrically between and spaced from the inner and outer housings 12 and 14. The design of the shim 20 is central to the invention. Referring to FIG. 2, there is shown a sectional view along longitudinal section II-II of FIG. 1. The same reference symbols identify corresponding elements throughout the draining. FIG. 2 shows the elements undeflected with the ogival longitudinal cross section of shim 20 clearly observable convex on both the side facing outer housing 14 and the side facing inner housing 12, the radius of curvature of both these surfaces preferably being the same. Referring to FIG. 3, there is shown essentially the same view as in FIG. 1, except that inner housing 12 is shown deflected clockwise relative to outer housing 14 by an angle ϑ₁ about pivot point A at the center of the bearing 10 about a radius A corresponding substantially to the inner radius of outer housing 14. Referring to FIG. 4, there is shown essentially the sectional view of FIGS. 2 and 3 except that inner member 12 is both axially displaced to the right relative to housing 14 and angularly displaced about pivot point B outside the housing clockwise by an incremental angle ϑ₂ about a radius R B greater than the radius R A . In an exemplary application R B is about 5R A . The invention thus allows relative angular displacement between the inner and outer housings about two different pivot points, one point A inside the bearing, the other pivot point B outside the bearing. In the relative angular displacement shown in FIG. 3 the rocking of inner housing 12 relative to that of outer housing 14 is essentially along the inside curved surface of shim 20. In the relative angular displacement shown in FIG. 4, the relative angular displacement is about both the inner and outer curved surfaces of shim 20. Referring to FIG. 5, there is shown a perspective view of shim 20. Referring to FIG. 6, there is shown a view through section VI-VI of the shim shown in FIG. 5 showing outside convex surface 20A of radius R₁ and the inner convex surface 20B of radius R₂. Referring to FIG. 7, there is shown another acceptable cross section for a shim 20' having end portions D and F of parallelogram cross section and the central portion E having curved inner and outside surfaces. The linear end portions D and F effectively limit the maximum relative angular deflection between inner housing 12 and outer housing 14. Referring to FIG. 8, there is shown a longitudinal sectional view of another embodiment of the invention having two concentric shims. In this embodiment there are three elastomer layers 18 sandwiching shims 31 and 32 having flat surfaces facing each other and convex surfaces facing the adjacent ones of inner housing 12 and outer housing 14 for shims 31 and 32, respectively. Referring to FIG. 9, there is shown a longitudinal sectional view of still another embodiment of the invention including a third shim 33 having flat surfaces on both sides between shims 31 and 32 and four elastomer layers 18. The present invention represents a practical solution to the problem of a bearing accommodating rotational motion about two different points comprising cocking motion taken in a compressive/tensile mode. For a conventional elastomeric bearing comprising an annular elastomer between inner and outer housings, such motion would cause delamination or greatly reduced fatigue life. With an intermediate shim member such as 20 of longitudinal cross section convey on both inside and outside surfaces, cocking compressive strains may be reduced to avoid a resulting short fatigue life while being embodied in a mechanical structure that is relatively easy and inexpensive to fabricate. Although the radii of curvature R₁ and R₂ may be unequal, they are preferably equal because cocking motion places both inboard and outboard layers of elastomer 18 in compression, and equalization of compression-induced strains results when R1=R2. It is also preferred that pivot point B be on the axis midway between the ends of the bearing. Otherwise, high tensile and compressive stresses at the bearing edges might well produce catastrophic failure.

Claims: A laminated compound support element (10) comprising: inner (12) and outer (14) concentric housings of substantially non-extensible material, and one layer of resilient material (18), interposed between said inner and said outer housings and having a thickness in its end portions which is greater than the thickness in its intermediate portion, characterized in that at least one further elastic layer (18) is provided between said inner (12) and said outer (14) concentric housings, the thickness of the end portions of said further (18) resilient layer being greater than the thickness of its intermediate portion, that at least one shim means (20;31,32) of substantially non-extensible material is provided between said one layer and said further resilient layer extending along the length thereof, and that said shim means has a longitudinal cross-section including a central portion (E) and linear end portions (D) and (F) for effectively limiting the maximum relative angular deflection and has at least one inside or outside convex surface, the shim means being bonded to the elastic layer and comprising a hollow tubular element. A laminated compound support element in accordance with claim 1, wherein said shim means (20) is characterized by a longitudinal cross section having both inside and outside convex surfaces facing said inside housing (12) and said outside housing (14) respectively, said resilient material (18) sandwiching said shim means. A laminated compound support element in accordance with claim 2, wherein the radius of curvature (R₁,R₂) of both said convex sufaces is substantially the same. A laminated compound support element in accordance with claim 3, wherein said shim means (20), said resilient means (18) and said housings coact to allow cocking of said inner housing (12) relative to said outer housing (14) about a first pivot point inside said element and a second pivot point outside said element. A laminated compound support element in accordance with claim 4, wherein said first pivot point is along the axis of said element midway between its ends and said second pivot point is in a plane perpendicular to the axis of said bearing and midway between its ends. A laminated compound support element in accordance with claim 2, wherein said shim means is formed with two concentric elements (31,32) separated by said resilient material (18). A laminated compound support element in accordance with claim 6, wherein said shim means further comprises an annular element between said concentric elements separated therefrom by said resilient means.

Inventors: O'DONNELL, BRIAN R., PERETTI, MARK F.
Applicants: BARRY WRIGHT CORPORATION
Application year: 1985
Main classification: F16C27
IPC codes: F16F1, B64C27