Patent Application
20200124097
The present disclosure is directed to an elastomeric bearing having a reduced-weight end cap and, more specifically, to an elastomeric bearing having and end cap formed with an at least partially hollow interior and/or by an additive manufacturing process.
Elastomeric bearings conventionally include a first race connected to a second race by a bearing body, and the bearing body is formed from alternating layers of a metal, such as stainless steel or titanium, and an elastomer. The first race may be an inner race disposed coaxially inside the second or outer race such that the alternating layers of the bearing body comprise coaxial cylinders with radii that increase from the inner ring to the outer ring. Alternately, the first race may be coaxially aligned with and axially spaced from the second race. In this case, the alternating layers of the bearing body comprise a stack of coaxial disks having substantially identical radii that extend from and connect the first and second races. When one race is fixed, the presence of the elastomer layers between the metal layers allows the second race to rotate around the common axis of the bearing by a few degrees or up to, in some cases, as much as 10 degrees, while substantially preventing the first race and second race from moving axially or radially relative to one another.
Elastomeric bearings have many uses, one of which is in a rotor assembly of a rotary wing aircraft. In this environment, the elastomeric bearing may connect a rotor blade to a support in a manner that allows the rotor blade to pivot up and down while limiting movement of the rotor blade in other directions. These bearings may be subjected to axial loads (axial relative to the bearing but in the radial direction of the aircraft rotor) of over 20,000 pounds when the rotor rotates and therefore must be constructed from materials that can withstand these forces. Additional information concerning elastomeric bearings and their use in rotary wing aircraft can be found, for example, in U.S. Pat. No. 7,097,169 to Mueller, the contents of which are hereby incorporated by reference.
It is desirable in many fields, including the field of rotary wing aircraft, to reduce weight in order to obtain improved performance and/or fuel efficiency. However, in view of the stresses experienced by the elastomeric bearings that support aircraft rotors, the weight reduction cannot come at the expense of strength or durability. Thus, for example, attempts have been made to reduce the weight of an elastomeric bearing for rotary wing aircraft by replacing the stainless steel layers in an elastomeric bearing with aluminum layers. While this change does reduce weight, a bearing with aluminum laminae lacks the strength to allow it to be used in a bearing for a rotary wing aircraft. That is, if aluminum is used, the bearing would be not be able to withstand the 20,000 pounds or more of axial force produced by the rotating blade. It is also known to use titanium instead of stainless steel, which is about 40% lighter than stainless steel. This arrangement provides a robust bearing but at a cost that is undesirably high for many applications.
It would therefore be desirable to provide an improved, lightweight elastomeric bearing that is sufficiently strong to allow it to be used to support a rotor in a rotary wing aircraft.
This problem and others are addressed by embodiments of the present disclosure, one aspect of which comprises an elastomeric bearing having a first race having an axis of rotation, a second race coaxially arranged relative to the first race and spaced from the first race by a gap, and a bearing body in the gap connecting the first race to the second race. The bearing body comprises a plurality of first laminae coaxial with the first race and a plurality of second laminae coaxial with the first race, and the first laminae are formed from a different material than the second laminae. The elastomeric bearing also includes a metal end cap connected to the first race or to the second race, and the metal end cap includes an at least partially hollow interior.
Another aspect of the disclosure comprises an elastomeric bearing that includes a first race having an axis of rotation, a second race coaxially arranged relative to the first race and spaced from the first race by a gap, and a bearing body in the gap connecting the first race to the second race. The bearing body comprises a plurality of first laminae coaxial with the first race and a plurality of second laminae coaxial with the first race, and the first laminae are formed from a different material than the second laminae. The elastomeric bearing also includes a metal end cap connected to the first race or to the second race, and the metal end cap is formed by an additive manufacturing process.
A further aspect of the disclosure comprises an elastomeric bearing that includes a first race having an axis of rotation, a second race coaxially arranged relative to the first race and spaced from the first race by a gap, and a bearing body in the gap connecting the first race to the second race. The bearing body comprises a plurality of elastomeric laminae coaxial with the first race and a plurality of carbon fiber reinforced polyether ether ketone laminae coaxial with the first race. The elastomeric bearing also includes a metal end cap connected to the first race or to the second race, and the metal end cap is formed by laser sintering. The end cap comprises an annular upper support member, an annular lower support member and a plurality of struts extending from the upper support member to the lower support member, and the plurality of struts are not perpendicular to the annular upper support and are not perpendicular to the annular lower support. The annular upper support member has an external diameter smaller than the external diameter of the annular lower support member. Also, the annular lower support member is located between the annular upper support member and the plurality of first laminae
These and other aspects of the present disclosure will be better understood after a reading of the following detailed description together with the attached drawings wherein:
Referring now to the drawings, wherein the showings are for the purpose of illustrating embodiments of the disclosure only and not for the purpose of limiting same,
One of the carbon fiber laminae 16 is illustrated by itself in
When the elastomeric laminae 14 and the carbon fiber laminae 16 are stacked, the convexities 32 of the elastomeric laminae 14 project into the concavities 26 of the carbon fiber laminae 16, and the convexities 24 of the carbon fiber laminae 16 project into the concavities 34 of the adjacent elastomeric laminae 14. While both the elastomeric laminae 14 and the carbon fiber laminae 16 could be planar, the presence of the concavities and convexities (or another interlocking shape) increases the surface area over which the laminae 14, 16 mutually contact each other and also helps align the laminae 14, 16 and allow the laminae 14, 16 to resist relative radial movement. In many embodiments, approximately 50 of the elastomeric laminae 14 are interleaved with a similar number of carbon fiber laminae 16 to form the elastomeric bearing 10.
In conventional elastomeric bearings, the laminae that are located between adjacent pairs of elastomeric laminae are formed from stainless steel or titanium. Other materials generally lack the strength required to withstand the stresses to which such elastomeric bearings are subjected when used, for example, to support the rotor blades of rotary wing aircraft. Specifically, it has been thought that materials other than stainless steel and titanium could not withstand the 20,000 pounds or more of centrifugal force produced by the rotating blades (a force directed along the axis of the bearing). However, the present inventors have discovered that carbon-fiber impregnated thermoplastics such as PEEK, in particular, multiple sheets 36 (
The individual sheets 36 that make up each carbon fiber lamina 16 may comprise tapes or webs of carbon fiber impregnated PEEK where the carbon fibers in each sheet 36 are aligned in a single direction (unidirectional). Preferably the five to nine sheets 36 that make up a carbon fiber lamina 16 are arranged with the fibers of each sheet 36 at a different angle. For example, the sheets 36 may be stacked so that the carbon fibers in one sheet run at a 90 degree angle to the fibers in each adjacent sheet 36. Alternately, the fibers in each sheet 36 may run at a 45 degree angle to the fibers in each adjacent sheet 36. This offset of the fibers in the adjacent sheets 36 increases the overall strength of the elastomeric bearing 10.
Reference is now made to
Forming the end cap 18 with a partially hollow interior instead of casting or otherwise forming the end cap 18 from a solid block of metal significantly reduces the weight of the end cap 18 and that of the bearing 10 itself. The structure 50, and, optionally, all external structures of the end cap 18, can be formed by an additive manufacturing process such as, for example, laser sintering. While manufacturing the end cap 18 from solid bodies of materials lighter than stainless steel has been considered, the use of a laser sintering or other additive manufacturing process allows for the end cap 18 to be formed with interior spaces that make up more than 5% of the interior volume or more than 50% of the interior volume or even as much about 90% of the interior volume of the end cap 18, significantly reducing the weight of the end cap 18.
Suitable materials for forming the end cap include stainless steel and titanium; however the former is generally preferred for reasons of cost. Thus according to this aspect of the disclosure, the weight of the end cap 18 can be reduced significantly without sacrificing the strength required to perform the function of an elastomeric bearing end cap in a support for the rotor blade of a rotary wing aircraft. When such an end cap is used with the novel carbon fiber reinforced laminae 16 described above, a 30-40% weight reduction over conventional elastomeric bearings is possible.
A second embodiment of the disclosure is shown in
The present invention has been described herein in terms of preferred embodiments. However, modifications and additions to these embodiments will become apparent to persons of ordinary skill in the relevant art upon a review of the foregoing description. It is therefore intended that all modifications and additions to these embodiments form a part of the present invention to the extent they fall within the scope of the several claims appended hereto.
