초록

An elastomeric spherical bearing includes a multiple of shims, at least two of which have different thicknesses. In one exemplary embodiment, each of the shims has a different thickness with an essentially equivalent stress on each shim.

대표청구항 ▼

1. A method of calculating a nonresilient shim thickness for a spherical elastomeric bearing comprising: determining a first thickness of a first of a multitude of nonresilient shim layers to satisfies a first set of criteria;determining a second thickness of a second of the multitude of nonresilien

1. A method of calculating a nonresilient shim thickness for a spherical elastomeric bearing comprising: determining a first thickness of a first of a multitude of nonresilient shim layers to satisfies a first set of criteria;determining a second thickness of a second of the multitude of nonresilient shim layers outboard of the first of the multitude of nonresilient shim layers to satisfies a second set of criteria, the second thickness different than the first thickness to produce a spherical elastomeric bearing generating an essentially equivalent stress to each nonresilient shim layer. 2. A method as recited in claim 1, further comprising: utilizing material strength allowables of each of the multitude of nonresilient shim layers at least in part as the first criteria and the second criteria. 3. A method as recited in claim 1, further comprising: sequentially iterating the thickness of each of the multitude of nonresilient shim layers until the multitude of nonresilient shim layers to generate an essentially equivalent stress in each of the multitude of nonresilient shim layers. 4. A method as recited in claim 1, wherein arranging each of the multitude of nonresilient shim layers relative to a bearing focal point such that each of the multitude of nonresilient shim layer increase in thickness relative a first inboard nonresilient shim layer. 5. A method of calculating a nonresilient shim layer thickness for a spherical elastomeric bearing comprising: determining a first shim thickness of a first of a multitude of nonresilient shim layers in the spherical elastomeric bearing, each of the multitude of nonresilient shim layers sandwiched between a first pair of elastomeric layers;determining a elastomeric layer thickness for the first pair of elastomeric layers; andmodifying the first shim thickness and the elastomeric layer thickness in response to an addition of a second a of the multitude of nonresilient shim layers and a second pair of elastomeric layers outboard of the first of the multitude of nonresilient shim layers and the first pair of elastomeric layers, the modifying continuing until each of the multitude of nonresilient shim layers have an essentially equivalent stress. 6. A method as recited in claim 5, further comprising: determining an axial load for the spherical elastomeric bearing in a direction parallel to a Z axis of rotation;determining a radial load in a radial direction for the spherical elastomeric bearing; anddetermining a vibratory pitch motion (θ) angle which rotates about the Z axis for the spherical elastomeric bearing. 7. A method as recited in claim 5, further comprising: utilizing a centrifugal force from a rotor blade as the axial load; andutilizing a shear load on the rotor blade as the radial load. 8. A method of calculating a nonresilient shim thickness for a spherical elastomeric bearing comprising: determining a first thickness of a first of a multitude of nonresilient shim layers to satisfies a first set of criteria;determining a second thickness of a second of the multitude of nonresilient shim layers outboard of the first of the multitude of nonresilient shim layers to satisfies a second set of criteria, the second thickness different than the first thickness;adjusting the shim hoop stress for each of the multitude of nonresilient shim layers to satisfy: σθ=4·(BI-(Bo-β))·(γa+γr)·G·D·π·E·cos⁡(Bs)·Rs1800·Te·Rs·sin⁡(Bs)·Ns·T(TTNs+1)·TTNs·T^s+TT·[[E·Ts⁡[cos⁡(Bs)]24·E·Ts312·(1-μ2)·[Rs·sin⁡(Bs)]2]1/4]-3to produce a spherical elastomeric bearing which generates an essentially equivalent stress to each nonresilient shim layer,where: T^e=Average⁢⁢Elastomer⁢⁢Thickness⁢⁢(Ti+Ti+1)2⁢(in)Ts=Shim Thickness Tsj (in){circumflex over (T)}s=Average Shim Thickness (in)μ=Shim Poison RatioE=Shim Modulus of Elasticity (psi)Rs=Shim Median Spherical Radius Rj (in) G=⁢Average⁢⁢Elastomer⁢⁢Shear⁢⁢Modulus⁢⁢(Gi+Gi+1)2⁢(psi)BI=Bearing Inner Wrap Angle (deg)Bo=Bearing Outer Wrap Angle (deg)Ns=Total Number of ShimsBs=Outer Wrap Around Angle of Shim Bsj (deg)D=Shim Bending Stiffness Term (lb-in)BET=Shim Geometric Stiffness Term (in)γ=Average Elastomer Compression Induced Shear Strain (in/in)/100TT=Total Bearing Elastomer Thickness (in)Q=Averaging Coefficient of Bearing (non-dimensional)ν=Averaging Coefficient of Elastomer To Shim Context (non-dimensional)LL=Unsupported Spherical Arc of Shim LLi (see FIG. 4)YY=Radial Deflection of Shim YYi (see FIG. 4)σθ=Shim Hoop Stress σθi (psi)DP=Differential Resultant Pressure Load On Unsupported Spherical Arc of Shim LLi Tc=Axial Compressive Load (lb)θ=Torsional Motion Angle (deg))β=Cocking Motion Angle (deg)Tc·sin·β=Radial Load (lb)RI=Bearing Inner Radius (in)Ro=Bearing Outer Radius (in)Tei=Elastomer Thickness (in)α=Bearing Outer Taper Angle (deg).