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  Braid construction to match coefficients of thermal expansion for composite transmission housingsUSPTO Application #: 20060148355Title: Braid construction to match coefficients of thermal expansion for composite transmission housings Abstract: A transmission assembly includes a composite transmission component with a tailored coefficient of thermal expansion (CTE). The composite transmission component is fabricated from graphite axial fibers and S-glass bias fibers that are oriented at a bias angle to the graphite axial fibers. The composite transmission component is located adjacent to a second composite transmission component and a metal transmission component. A first CTE of the composite transmission component is tailored to a CTE of the second composite component. A second CTE of the composite transmission component is tailored to a metal CTE of the metal transmission component. The first and second CTE are tailored by utilizing graphite axial fibers and S-glass bias fibers, or two other different types of fibers, and by controlling the bias angle. The tailored first and second CTE minimize thermal strain and maintain a tight fit between the components. (end of abstract) Agent: Carlson, Gaskey & Olds, P.C. - Birmingham, MI, US Inventors: Geoffrey Clive Robert Davis, Jonathan Kent Garhart USPTO Applicaton #: 20060148355 - Class: 442209000 (USPTO) Related Patent Categories: Fabric (woven, Knitted, Or Nonwoven Textile Or Cloth, Etc.), Woven Fabric (i.e., Woven Strand Or Strip Material), Woven Fabric Is Characterized By A Particular Or Differential Weave Other Than Fabric In Which The Strand Denier Or Warp/weft Pick Count Is Specified, Warp Differs From Weft, Materials Differ The Patent Description & Claims data below is from USPTO Patent Application 20060148355. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] This invention relates to transmission housings and, more particularly, to a composite transmission housing component with a tailored coefficient of thermal expansion (CTE). [0002] Conventional power transmissions and transmission components may potentially use light-weight composite materials to reduce the weight of the power transmission, however, some components such as gears, bearing liners, and bearing races are still made from metal materials. [0003] The use of composite components and metallic components in intimate contact with each other may present problems over the operating temperature range of the power transmission. Typically, the composite component has a different CTE than the metal component. The difference in CTE causes the composite component to expand and contract over a temperature range differently than the metal component expands and contracts. When the composite component and metal component are bonded together or otherwise meet at a composite-metal interface, the difference in CTE may cause thermal strain between the composite component and the metal component, which in turn may lead to a failure at the composite-metal interface. Common interface failures include physical separation between the composite component and metal component, aggravated fatigue and creep, formation of leak paths, and loosening of press fits, all of which may affect the proper functioning of the power transmission. The problem is further compounded with an additional composite-composite interface when another composite component with yet another CTE is located next to the first composite component. [0004] Some existing conventional composite materials have been designed with a CTE that is closer to the CTE of most metals. Reducing the difference between the CTE of the composite and the CTE of the metal may alleviate the thermal strain and may reduce risk of failure at a composite-metal interface. These conventional composites typically include stacking positive and negative CTE composite layers, using specialized and expensive fibers, or orienting the reinforcing fibers to tailor the CTE in a single direction. [0005] Although these conventional composites may alleviate thermal strain problems for composite-metal interfaces, a conventional composite may actually aggravate thermal strain problems in a power transmission application where the composite component also interfaces with another different type of composite component by increasing the difference between the CTE's of the two composite components. Despite these conventional composites, a demand remains for a composite that is thermally compatible with both metals and other composites. [0006] Accordingly, a composite component having a CTE that more effectively matches the CTE of an interfacing metal component and the CTE of another interfacing composite component is needed. SUMMARY OF THE INVENTION [0007] The transmission assembly according to the present invention includes a composite transmission component with a tailored coefficient of thermal expansion (CTE). The composite transmission component is located adjacent to another composite component and a metal component and is thermally compatible with both the other composite component and the metal component. [0008] In each of the transmission assembly examples considered, the composite transmission component is fabricated from braid employing graphite axial fibers and S-glass bias fibers that are oriented at a bias angle to the graphite axial fibers. This configuration produces a structure with two directionally dependant coefficients of thermal expansion. The composite transmission component is located adjacent to a second composite transmission component and a metal transmission component. A first CTE of the composite transmission component is tailored to a CTE of the second composite component and a second CTE of the composite transmission component is tailored to a metal CTE of the metal transmission component. The first and second CTE are tailored by utilizing graphite axial fibers and S-glass bias fibers, or two other different types of fibers, and by controlling the bias angle. [0009] In one composite transmission component example, the composite transmission component is positioned radially inward from the metal transmission component. The first CTE is tailored to be generally equal to the CTE of the second composite component in an axial direction and the second CTE is tailored to be slightly greater than or equal to the CTE of the metal transmission component in a hoop direction to minimize thermal strain between all the components and to maintain a tight fit between the composite transmission component and the metal transmission component. [0010] In another composite transmission component example, the composite transmission component is positioned radially outward from the metal transmission component. The first CTE is tailored to be generally equal to the CTE of the second composite component in an axial direction and the second CTE is tailored to be slightly greater than or equal to the CTE of the metal transmission component in a hoop direction to minimize thermal strain between all the components and to maintain a tight fit between the composite transmission component and the metal transmission component. [0011] The transmission according to the present invention provides a composite component that is thermally compatible with another composite component and a metal component. BRIEF DESCRIPTION OF THE DRAWINGS [0012] The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. [0013] FIG. 1 illustrates a schematic perspective view of an example vehicle with a transmission housing; [0014] FIG. 2 illustrates a perspective cross-sectional view of the transmission of FIG. 1; [0015] FIG. 3 illustrates a perspective cross-sectional view of a tail take-off drive of the transmission of FIG. 1; and [0016] FIG. 4 illustrates a schematic view of a triaxially braided fiber reinforced composite. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0017] FIG. 1 schematically illustrates a rotary-wing aircraft 10 having a main rotor assembly 12. The aircraft 10 includes an airframe 14 having an extending tail 16 which mounts an anti-torque rotor 18. The main rotor assembly 12 is driven through a transmission (illustrated schematically at 20) by one or more engines 22. Although a particular helicopter configuration is illustrated in the disclosed embodiment, other machines such as turbo-props, tilt-rotor and tilt-wing aircraft will also benefit from the present invention. [0018] Referring to FIG. 2, the transmission 20 includes a transmission housing 30. The transmission housing 30 includes a composite outer structure 32 which is preferably fabricated from a graphite fiber reinforced composite. The composite outer structure 32 structurally supports an adjacent first composite support 34 and tail rotor take off drive 36. [0019] The first composite support 34 is annular in shape and defines an axis 38. A bull gear 40 with a steel bearing races 41 is mounted on the first composite support 34. The bull gear 40 is located radially outward from the first composite support 34 such that the bull gear 40 and first composite support 34 meet at an interface 42. The interface 42 extends in a circumferential hoop direction 44 relative to the axis 38. The composite outer structure 32 and first composite support 34 meet at an interface 46 which extends primarily in an axial direction that is generally parallel with the axis 38. [0020] Referring to FIG. 3, the tail rotor take off drive 36 includes a drive gear 56 defining an axis 58. Steel bearing races 60 and titanium or steel metal bearing liners 62 are mounted radially inward relative to a second composite support 64 such that the bearing races 60, bearing liners 62, and second composite support 64 meet at an interface 66. The interface 66 extends in a circumferential hoop direction 68 relative to the axis 58. The composite outer structure 32 and second composite support 64 meet at an interface 70 which extends primarily in an axial direction that is generally parallel the axis 58. Continue reading... Full patent description for Braid construction to match coefficients of thermal expansion for composite transmission housings Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Braid construction to match coefficients of thermal expansion for composite transmission housings patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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