Patent Description:
Composite materials exhibit significant weight efficiency with respect to strength and stiffness properties in comparison with more conventional metals and alloys. Thus, composite materials are extremely attractive for numerous aircraft structures, including drive shafts. Drive shafts usually represent straight structural elements with a cylindrical hollow shape having constant or variable circular cross-section. Composite shafts are typically formed by polymer-matrix fiber-reinforced materials fabricated about a mandrel. The polymer and fiber material combine to form a wall thickness of the shaft that drives one or more strength and stiffness properties needed to satisfy design criteria such as structural integrity. The thicker the wall, the more resistant the shaft is to applied loads. However, additional wall thickness also contributes to increased weight and cost. Therefore, there is a need to design and fabricate composite drive shafts with relatively thin walls and correspondingly lower weight, but at the same time, reliable enough to sustain service conditions.

Composite shafts showing different designs of internal support members are shown in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. <CIT> shows the preamble of claim <NUM>.

Torque is usually a dominant load component for drive shafts, although some bending and axial load components can also be considered. Therefore, torque-specific potential failure mechanisms should be considered as additional design criteria for composite shafts. One such potential failure mechanism under torque is buckling, i.e., conditions where the shape and/or geometry of the shaft are disproportionally deformed. Buckling is an indicator of unstable load transfer. Corresponding large deformations during buckling are reflected in higher stresses leading to premature shaft damage. Risk of buckling under torque is of greater concern in composite shaft design. That is, in a composite shaft reinforced fiber strength allows for shaft design to include relatively thin walls while maintaining axial loading load properties. However, the thin walls may not possess a desired buckling resistance. Therefore, the industry would welcome a composite shaft design that possesses both a thin wall and also resists buckling.

Disclosed is a composite shaft including a shaft body formed from a plurality of polymer impregnated fiber-reinforced material layers having an annular outer surface and an annular inner surface defining a passage. A plurality of internal support members extend along the passage. Each of the plurality of internal support members includes a support body formed from molded plastic having an outer surface that abuts the annular inner surface of the shaft body, a first end, an opposing second end, and a circular end wall arranged at one of the first end and the opposing second end.

Additionally, or alternatively, in this or other non-limiting examples, the plurality of internal support members includes a first internal support member and a second internal support member, the first internal support member abutting the second internal support member in the passage.

Additionally, or alternatively, in this or other non-limiting examples, two or more of the internal support members are joined together.

Additionally, or alternatively, in this or other non-limiting examples, wherein the circular end wall of the first internal support member includes a first opening and the circular end wall of the second internal support member includes a second opening that aligns with the first opening.

Additionally, or alternatively, in this or other non-limiting examples, a rod extending through the first opening and the second opening, the rod joining the first internal support member and the second internal support member.

Additionally, or alternatively, in this or other non-limiting examples, the first internal support member includes a first circular end wall at the first end and a second circular end wall at the opposing second end, and the second internal support member includes a first circular end wall portion at the first end and a second circular end wall portion at the opposing second end.

Additionally, or alternatively, in this or other non-limiting examples, the first internal support member includes a first length defined between the first circular end wall and the second circular end wall and the second internal support member includes a second length defined between the first circular end wall portion and the second circular end wall portion, the second length being distinct from the first length.

Additionally, or alternatively, in this or other non-limiting examples, the second circular end wall includes an axially inwardly extending portion that extends inward from the second end and the first circular end wall portion includes an axially outwardly extending portion that extends outwardly of the first end and nests within the axially inwardly extending portion.

Additionally, or alternatively, in this or other non-limiting examples, the annular outer surface of the shaft body includes a radially outwardly extending projection and the annular inner surface of the shaft body includes a pocket defined by the radially outwardly extending projection.

Additionally, or alternatively, in this or other non-limiting examples, the support body of the internal support member includes a radially outwardly projecting portion extending into the pocket, the radially outwardly projecting portion being defined by the outer surface.

According to the invention, one of the first and the second circular end walls is formed by a plurality of ribs that radiate outwardly from a central hub to the inner surface.

Additionally, or alternatively, in this or other non-limiting examples, the one of the first and second circular end walls includes a circumferentially extending rib that extends about and is spaced from the central hub.

Also disclosed is an example method of making a composite shaft. The method includes forming an internal support member having an outer surface, an annular inner surface, and a circular end wall by expanding an amount of thermoplastic material in an internal support member mold, removing the internal support member from the internal support member mold, providing the internal support member in a passage of the composite shaft with the outer surface abutting the annular inner surface of the composite shaft, and providing additional internal support members in the passage with one or more of the additional internal support members abutting the internal support member.

Additionally, or alternatively, in this or other non-limiting examples, the method may also include forming the internal support member and the additional internal support members into a mandrel, and forming the composite shaft around the mandrel.

Additionally, or alternatively, in this or other non-limiting examples, the method may also include joining the internal support member with the additional internal support members in the passage.

Additionally, or alternatively, in this or other non-limiting examples joining the internal support member with the additional internal support members includes positioning an axially outwardly extending portion on the internal support member into an axially inwardly extending portion formed in one of the additional internal support members.

Additionally, or alternatively, in this or other non-limiting examples, joining the internal support member with the additional internal support members includes passing a rod through the internal support member and the additional internal support members.

Additionally, or alternatively, in this or other non-limiting examples, the method may also include applying a compressive force to the internal support member and the additional internal support members through the rod.

Additionally, or alternatively, in this or other non-limiting examples, forming the internal support member includes forming the circular end wall with a plurality of ribs that extend outwardly from a hub to the annular inner surface.

Additionally, or alternatively, in this or other non-limiting examples, forming the internal support member includes forming the circular end wall with a plurality of ribs that extend outwardly from a hub to the annular inner surface and a circumferentially extending rib that extends about and spaced from the hub.

A detailed description of one or more non-limiting examples of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

With initial reference to <FIG>, a rotary wing aircraft is indicated generally at <NUM>. Rotary wing aircraft <NUM> includes a fuselage <NUM> that supports a main rotor assembly <NUM> having a main rotor gear box <NUM>, and a tail rotor <NUM> having a tail rotor gear box <NUM>. Rotary wing aircraft <NUM> can include a first engine <NUM> and a second engine <NUM>. A first drive shaft system <NUM> extends between first engine <NUM> and a main rotor gear box <NUM>. A second drive shaft system <NUM> extends between second engine <NUM> and main rotor gear box <NUM>. A tail rotor drive shaft system <NUM>, which may be made up from multiple tail rotor drive shaft sections (not separately labeled), extends between main rotor gear box <NUM> and an intermediate gear box <NUM>. A pylon drive shaft system <NUM> extends between intermediate gear box <NUM> and tail rotor gear box <NUM>.

In a non-limiting example, tail rotor drive shaft system <NUM> takes the form of a composite shaft <NUM> made up from multiple fiber-reinforced polymer-matrix layers as shown in <FIG>. At this point, it should be understood that while described in connection with a rotary wing aircraft, the composite shaft <NUM> described herein may also be employed in fixed wing aircraft as well as other applications that would benefit from enhanced buckling resistance.

As an example, composite shaft <NUM> may be made, for example, from carbon, glass, organic fibers, or any of their combinations. The polymer matrix of the composite shaft <NUM> can be either thermoplastic or thermoset. At this point, it should be understood that first drive shaft system <NUM>, second drive shaft system <NUM>, and pylon drive shaft system <NUM> may also take the form of composite shafts. With continued reference to <FIG>, composite shaft <NUM> includes a shaft body <NUM> having an annular outer surface <NUM> and an annular inner surface <NUM> that defines a passage <NUM>. A plurality of internal support members, one of which is indicated at <NUM>, extend along passage <NUM>.

Referring to <FIG> and with continued reference to <FIG>, each internal support member <NUM> includes a support body <NUM> having an outer surface <NUM> that extends between a first end <NUM> and a second end <NUM>. A first circular end wall <NUM> is arranged at first end <NUM> and a second circular end wall <NUM> is arranged at second end <NUM>. Support body <NUM> further includes an inner surface <NUM> which defines a chamber <NUM> that is devoid of other materials, in accordance with an exemplary aspect. An opening <NUM> is provided in first circular end wall <NUM>. Opening <NUM> may be a remnant of fabrication. That is, support body <NUM> is a unitary piece that is formed from, for example, gas-assisted or blow-molded thermoplastic. At this point, it should be understood that as used herein "unitary piece" as applied to an internal support member <NUM> describes an internal support member <NUM> with a support body <NUM> where outer surface <NUM>, inner surface <NUM>, first circular end wall <NUM> and second circular end wall <NUM> are formed from a single, continuous piece of material.

At this point, it should be understood that internal support members <NUM> may take on a variety of forms. Non-limiting examples are shown in <FIG>. For example, in <FIG>, support body <NUM> may include a first circular end wall <NUM> having a closed opening. In <FIG>, support body <NUM> includes a first circular end wall <NUM> with large opening that takes the form of a flange <NUM>. In <FIG>, support body <NUM> includes a second circular end wall <NUM> with large opening in the form of a flange <NUM> and a first circular end wall <NUM> having a small opening <NUM> left over from, for example, fabrication. In <FIG>, support body <NUM> includes a second circular end wall <NUM> and a first circular end wall <NUM> each with large openings and in the form of a flange <NUM> and <NUM> respectively. In <FIG>, support body includes a second circular end wall <NUM> and a first circular end wall <NUM> each having a small opening <NUM> and <NUM> respectively that may be left after fabrication.

In <FIG>, an internal support member <NUM> is shown to include a support body <NUM> having an outer surface <NUM> formed with an annular undulated shape, shown as rib <NUM>. The undulated shape provides enhanced bending flexibility, without detracting from torsional stiffness. It should be understood that the number, size, and shape of ribs <NUM> may vary. When multiple ribs are employed, each rib may be similarly sized and shaped or may possess different sizes and/or shapes. Similarly, it should be understood that support members may vary in construction depending on specific design requirements and goals.

Referring to <FIG>, internal support members, such as those shown in <FIG> may be joined by a rod <NUM> having ends <NUM> and <NUM>. Fasteners <NUM> and <NUM>, or other structures, mounted to ends <NUM> and <NUM> may be manipulated, e.g., tightened, to apply a compressive force to the internal support members <NUM>. Fasteners <NUM> and <NUM> can be mounted to ends <NUM> and <NUM> by various mechanisms including, for example, interlocking threads. The compressive force may establish a preload or may be utilized as a holding force as internal support members are connected and bonded together. Note that while <FIG> illustrates an arrangement of support members <NUM> such as shown in <FIG>, it should be understood that other support member configurations may be joined in a similar manner. It should also be appreciated that, in accordance with a non-limiting example, internal support members may be joined on to another by an adhesive, sonic welding, thermal welding or other systems that may be employed to join thermoplastic or joined together by axial pressure, provided, for example, by rod <NUM>.

In <FIG>, internal support members <NUM> such as shown in <FIG> are aligned and a composite shaft <NUM> is formed about outer surface <NUM>. Composite shaft <NUM> includes a number of radially outwardly extending annular projections <NUM> each of which forms a corresponding annular internal pocket <NUM> receptive of annular rib <NUM>. The annular ribs <NUM> and projections <NUM> combine to enhance axial bending flexibility of composite shaft <NUM> as may be desired for various design configurations.

<FIG> depict additional non-limiting examples of internal support members. In particular, internal support members having first and second circular end walls with different geometries. For example, in <FIG>, an internal support member <NUM> include a first circular end wall <NUM> and a second circular end wall <NUM> each having a corresponding axially inwardly extending portions <NUM> and <NUM>. A chamber (not separately labeled) is defined between second circular end wall <NUM> and a first circular end wall of an abutting internal support member. In <FIG>, an internal support member <NUM> includes first and second circular end walls <NUM> and <NUM> each of which define corresponding first and second axially outwardly extending projections <NUM> and <NUM>. Axially outwardly extending projections <NUM>/<NUM> extend along a central longitudinal axis "A" of composite shaft <NUM>. In this arrangement, first axially outwardly extending projection <NUM> may nest within the axial inwardly extending projection <NUM> defined in, internal support member, <NUM>.

In <FIG>, a first internal support member <NUM> is shown to include a first circular end wall <NUM> including an axially outwardly extending projection <NUM> and a second circular end wall <NUM> defining an axially inwardly extending projection <NUM>. Axially outwardly extending projection <NUM> extends away from first internal support member <NUM> along central longitudinal axis "A' while axially inwardly extending projection <NUM> extends into first internal support member <NUM> along central longitudinal axis "A". A second internal support member <NUM> is similarly formed. For example, second internal support member <NUM> includes a first circular end wall portion <NUM> including an axially outwardly extending portion <NUM> and a second circular end wall portion <NUM> defining an axially inwardly extending projection <NUM>. Axially outwardly extending projection <NUM> extends away, relative to second internal support member <NUM> along central longitudinal axis "A" while axially inwardly extending projection <NUM> extends into second internal support member <NUM> along central longitudinal axis "A".

In <FIG>, an internal support member <NUM> is shown to include a first circular end wall <NUM> that may include an opening <NUM> and a second circular end wall <NUM> that includes an axially inwardly extending portion <NUM> which may include an opening <NUM>. Axially extending inwardly extending portion <NUM> extends into internal support member <NUM> along central longitudinal axis "A". A chamber (not separately labeled) may be defined between second circular end wall <NUM> and a first circular end wall of an abutting internal support member. The various geometries may be interchanged and combined to establish various flexibility qualities of the associated composite shaft.

Further, in <FIG> a first internal support member <NUM> is shown to include a first circular end wall <NUM> spaced from a second circular end wall <NUM> by a first length and a second internal support member <NUM> having a first circular end wall portion <NUM> spaced from a second circular end wall portion <NUM> by a second length that is distinct from the first length. Thus, it should be understood that internal support members of varying lengths may be combined to accommodate various lengths of composite shafts. Similarly, different internal support members can have different wall thicknesses or other geometrical characteristics, e.g., local curvatures. In <FIG> an internal support member <NUM> having an annular outer surface <NUM> may be combined with an internal support member <NUM> having an annular undulated rib <NUM> in a composite shaft <NUM>. The number of, and spacing between support members may vary in order to achieve a selected flexibility characteristic and yet still withstand applied load conditions.

Reference will now follow to <FIG> in describing an internal support member <NUM> that may be incorporated into composite shaft <NUM> in accordance with another non-limiting example. Internal support member <NUM> includes an annular outer surface <NUM> and an inner surface <NUM>. Internal support member <NUM> includes a first circular end wall <NUM> and a second circular end wall <NUM>. First circular end wall <NUM> is substantially solid but for, in accordance with a non-limiting example, a central opening <NUM>. Second circular end wall <NUM> is formed by a plurality of ribs, one of which is indicated at <NUM> that radiate outwardly from a central support <NUM> and connector with inner surface <NUM>. Each rib <NUM> may generally have different cross-sectional shapes, such as a curvilinear cross-section shown in <FIG> in accordance with a non-limiting example. Ribs <NUM> increase the bending stiffness of second circular wall end <NUM> to thereby improve localized buckling resistance at second circular end wall <NUM> and potential local buckling of, for example, internal support member <NUM>.

An internal support member <NUM> in accordance with another non-limiting example is shown in <FIG>. Internal support member <NUM> includes an annular outer surface <NUM> and an inner surface <NUM>. Internal support member <NUM> also includes a first circular end wall <NUM> and a second circular end wall <NUM>. First circular end wall <NUM> is formed from a plurality of ribs, one of which is indicated at <NUM>, that radiate outwardly from a central hub <NUM> to inner surface <NUM>. Central hub <NUM> may include an opening <NUM>. Similarly, second circular end wall <NUM> formed by a plurality of ribs, one of which is indicated at <NUM> that radiate outwardly from a central hub <NUM> and connect with inner surface <NUM>. Central hub <NUM> may include an opening <NUM>. In a non-limiting example, ribs <NUM> and ribs <NUM> may have a generally flat cross section or possess a generally curvilinear cross-section. At this point, it should be understood that the number and arrangement of ribs may vary.

<FIG> depicts an internal support member <NUM> having an outer surface <NUM> and an inner surface <NUM>. Internal support member <NUM> includes at least one circular end wall <NUM> formed by a plurality of ribs, one of which is indicated at <NUM> that project radially outwardly from a central hub <NUM> to inner surface <NUM>. Circular end wall <NUM> also includes a circumferentially extending rib <NUM> that extends about, and is spaced from, central hub <NUM>. Circumferentially extending rib <NUM> connects with each of the plurality of ribs <NUM>. At this point, it should be understood that the number and arrangement of ribs may vary. Also, in addition to radial ribs <NUM> and circumferential ribs <NUM> other geometrical and topological designs of a plurality of ribs may be employed. Further, it should be appreciated that the ribs and central support provide desired stiffness and strength characteristics for a composite shaft.

Reference will now follow to <FIG> in describing a method of fabricating an internal support member in accordance with a non-limiting example. An internal support member mold <NUM> includes an outer surface <NUM> and an inner surface <NUM> that defines a chamber <NUM>. Internal support member mold <NUM> includes a first end wall <NUM> and a second end wall <NUM>. First end wall <NUM> includes a first opening <NUM> and second end wall <NUM> can include an optional second opening <NUM>. Such molds consists of several parts kept together during fabrication of an insert, but disjointed after the fabrication to remove a manufactured insert.

As shown in <FIG>, an amount of thermoplastic in the form of a thermoplastic blank <NUM> having an inlet <NUM> is positioned in chamber <NUM>. Inlet <NUM> is passed through first opening <NUM>. Thermoplastic blank <NUM> is heated inside mold chamber <NUM> at or above a softening or melt temperature upon which an amount of a gas <NUM> is delivered through inlet <NUM> causing thermoplastic blank <NUM> to expand and take on a shape of chamber <NUM>. As thermoplastic blank <NUM> expands and forms the internal support member shape, air in chamber <NUM> may escape through first opening <NUM> and/or second opening <NUM>. Thermoplastic blank <NUM>, now in the form of an internal support member, is cooled and removed from internal support member mold <NUM> for later incorporation into a composite shaft.

Methods of follow-up forming of composite shaft around a supporting member or a plurality of supporting members can be different and based on specifics of designs shafts, applied load conditions and other parameters, such as cost, availability of needed equipment, availability of trained manpower and suppliers, etc. Among such methods, the Automated Fiber Placing (AFP), filament wounding and braiding can be employed. When using internal support members without undulated ribs, wrapping of composite shaft can be employed as well.

At this point, it should be understood that the non-limiting examples presented herein describe a composite shaft that resists buckling forces. The composite shaft includes a series of internal support members that are designed to provide a resistance to buckling forces yet remain lightweight and flexible. Further the internal support members may be formed to include different geometries and sizes in order to meet particular reinforcement, weight, and flexibility requirements.

The terms "about" and "substantially" are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, "about" and/or "substantially" can include a range of ± <NUM>% or <NUM>%, or <NUM>% of a given value.

Claim 1:
A composite shaft (<NUM>) comprising:
a shaft body (<NUM>) formed from a plurality of polymer impregnated fiber-reinforced material layers having an annular outer surface (<NUM>) and an annular inner surface (<NUM>) defining a passage (<NUM>); and
a plurality of internal support members (<NUM>) extending along the passage (<NUM>), each of the plurality of internal support members including a support body (<NUM>) formed from molded plastic having a continuous outer surface (<NUM>) that extends circumferentially about and abuts the annular inner surface (<NUM>) of the shaft body (<NUM>), a
continuous inner surface (<NUM>), a first end (<NUM>), an opposing second end (<NUM>), and a circular end wall (<NUM>, <NUM>) arranged at each of the first end (<NUM>) and the opposing second end (<NUM>), the circular end wall (<NUM>, <NUM>) extending radially inwardly from the continuous inner surface at corresponding ones of the first end and the opposing second end,
characterized in that
one of the first and the second circular end walls is formed by a plurality of ribs (<NUM>) that radiate outwardly from a central hub (<NUM>) to the inner surface.