Patent Description:
Leadscrews and nuts may be used in aircraft and avionic application for various actuations. Such actuators can include, for example, doors, flaps, thrust reverses, and the like. Conventionally, such actuators may be formed of metallic leadscrews and nuts. However, such metal-to-metal configurations can cause excess wear and/or may require additional features, such as lubrication and the like. One alternative to such metal-metal actuators is to use plastics. However, engineered plastic nuts against metallic leadscrews may have higher limiting pressure-velocity ("pv"), efficiency, low wear rate, etc., as compared to metal-metal configurations (e.g., bronze nut and metallic screws) in an unlubricated environment under low load application. An alternative is to use a polymer nut with a metallic leadscrew, which due to their low wear behavior, may be considered as low a cost alternative to metallic ball screw based drives. However, improved actuators that use a leadscrew-nut configuration may be beneficial.

According to some embodiments, leadscrew and nut actuators are provided. The leadscrew and nut according to the invention includes a leadscrew having an external thread and formed from a first material, a nut configured to receive the leadscrew, the nut having an internal thread and formed from a second material, and an insert arranged between the internal thread of the nut and the external thread of the leadscrew, the insert configured to transfer force between the external thread and the internal thread and prevent material contact between the leadscrew and the nut. The insert is formed of a third material different from the first material and the second material.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the first material and the second material are metals.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the first material and the second material are the same material.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the third material is a polymer.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the insert has a helical structure.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the insert is fixedly attached to the nut within the internal thread.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the insert is fixedly attached to the leadscrew within the external thread.

According to the invention, the actuator includes at least one end stop fixedly attached to the leadscrew and arranged within a space between axially adjacent portions of the external thread and configured to retain the position of the insert relative to the leadscrew.

Alternatively, the actuator according to the invention includes at least one end stop fixedly attached to the nut and arranged within a space between axially adjacent portions of the internal thread and configured to retain the position of the insert relative to the nut.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the external thread defines a space between axially adjacent portions of the external thread, wherein the space has a geometric profile and the insert has a cross-sectional shape that matches the geometric profile of the space.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the internal thread defines a space between axially adjacent portions of the internal thread, wherein the space has a geometric profile and the insert has a cross-sectional shape that matches the geometric profile of the space.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the insert has a rounded cross-sectional shape.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the insert has a squared cross-sectional shape.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include an additional insert arranged between the internal thread of the nut and the external thread of the leadscrew.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the leadscrew is operably connected to a component of an aircraft.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the nut is operably connected to a component of an aircraft.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that at least one of the leadscrew and the nut are formed of a corrosion resistant steel, titanium, a non-corrosion resistant steel, and a copper based alloy.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the insert is formed from one of Polyamides, PEEK, PAEK, and PTFE.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the material of the insert includes a filler.

In addition to one or more of the features described herein, or as an alternative, further embodiments of the leadscrew and nut actuators may include that the filler comprises graphite or carbon.

The foregoing and other features, and advantages of the present <NUM>. invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:.

Referring to <FIG>, a schematic illustration of an aircraft <NUM> that may incorporate embodiments of the present invention is shown. The aircraft <NUM> includes a fuselage <NUM>, wings <NUM>, and a tail <NUM>. In this illustrated embodiment, the aircraft <NUM> includes wing-mounted aircraft power systems <NUM>. The wing-mounted aircraft power systems <NUM> may be conventional gas turbine engines or other propulsion systems as known in the art. In other configurations, aircraft employing embodiments of the present disclosure may include fuselage-mounted and/or tail-mounted configurations. The aircraft power systems <NUM> may be used to generate thrust for flight and may also be used to generate onboard electrical power. The aircraft <NUM> may also include one or more auxiliary power units <NUM> that may be configured to generate power. The aircraft <NUM> includes doors <NUM> and aircraft flight control surfaces <NUM> (e.g., ailerons, flaps, flaperons, stabilizers, etc.). Additionally, the aircraft power systems <NUM> may include thrust reversers <NUM>, as will be appreciated by those of skill in the art.

Control or actuation of various components of the aircraft <NUM> may be enabled through use of actuators. Actuators onboard aircraft can be used for, for example, actuating the doors <NUM>, the flight control surfaces <NUM>, the thrust reversers <NUM>, landing gear, interior doors, seats, and the like. The actuators may be configured as leadscrew and nut configurations. These actuators are typically linear actuators that rotate a nut to drive the leadscrew in an axial direction along an axis of the leadscrew.

Referring now to <FIG>, an actuator <NUM> that may incorporate embodiments of the present invention is shown. <FIG> shows part of an engine housing <NUM> including a door <NUM> moveable between a closed position and an open position. In <FIG>, the door <NUM> is shown in its open position. The actuator <NUM> is arranged to drive the door <NUM> between the closed position and the open position. In the example shown, the actuator <NUM> is in the form of a linear actuator including a housing <NUM> that contains a nut <NUM>. The nut <NUM> is rotatable within the housing <NUM> and drives linear motion of a leadscrew <NUM>. By rotating the nut <NUM>, the leadscrew will translate, extension and retraction, to drive the door <NUM> between the closed position and the open position. This type of actuation may be used for any controllable component onboard an aircraft, such as the various components described above and as appreciated by those of skill in the art.

The nut <NUM> may be formed of an engineered plastic that is arranged against a metallic leadscrew. Such a configuration may have higher limiting pressure-velocity ("pv"), efficiency, low wear rate, etc. as compared to metal-metal (e.g., bronze nut and metallic screw) configurations in an unlubricated environment under low load applications. However, due to their low wear behavior, polymer nuts with a metallic lead screw are considered low cost alternatives to metallic ball-screw based drives. However, such configurations are currently used for low load applications. It may be advantageous to incorporate polymers to improve operation of leadscrew-nut actuators.

Designing thread root features of plastics nuts for high load applications is a challenge due to their tensile and fatigue strength capability of polymer components. For example, contact pressure at a joint interface of a screw and a nut influences the friction coefficient and wear behavior of the interface, and such wear can cause early failure or shorten part life of such components. A wide thread flank can reduce contact pressure at the interface, however, designing a wide flank is a challenge as it further worsens the stresses at the thread root features.

In view of this and other considerations, a machined or molded helical insert made of engineered polymers can be incorporated into a metal-metal actuator. When placed between a metallic nut and a metallic leadscrew, the insert can prevent metal to metal contact, thus enabling achieving a high load system that incorporates the advantages of a plastic or polymer system. In the present invention, the insert(s) are held captive within the nut or to the leadscrew by mechanical or bonding means. Such captive inserts will prevent such inserts from winding out during actuation of the leadscrew. Further, in some embodiments, multiple inserts can be assembled in series to share loads and thus increase an overall load capability of the system.

Turning now to <FIG>, schematic illustrations of an actuator <NUM> in accordance with an embodiment of the present invention are shown. The actuator <NUM> may be configured for use onboard an aircraft and may be installed and arranged to enable actuation or operation of one or more components, systems, or devices onboard the aircraft.

The actuator <NUM> includes a leadscrew <NUM> and a nut <NUM>. The leadscrew <NUM> includes an external thread <NUM> and the nut <NUM> includes an internal thread <NUM>. The nut <NUM> is arranged within a housing <NUM>. In some embodiments, the nut <NUM> is fixedly attached or connected to the housing <NUM>. The leadscrew <NUM> may be operably connected at one or both ends to surfaces and/or structures of an aircraft, with such surface and/or structure, or part thereof, configured to be moved or actuated by linear or axial movement of the leadscrew <NUM> along an axis A.

In operation, the nut <NUM> may be rotated to drive axial movement of the leadscrew <NUM>. In other configurations, the axial movement of the leadscrew <NUM> may drive rotation of the nut <NUM>. In such configuration, the component/structure/feature to be driven by the actuator <NUM> may be operably coupled to the nut <NUM> and/or the housing <NUM>. It will be appreciated that the specific output operation (e.g., from leadscrew <NUM> or nut <NUM>) is not intended to be limiting, but rather is reflective of the specific application and intended use of the actuator <NUM>.

In the actuator <NUM> of the invention, an insert <NUM> is arranged between the leadscrew <NUM> and the nut <NUM>. The insert <NUM> is configured to fit between the external thread <NUM> of the leadscrew <NUM> and the internal thread <NUM> of the nut <NUM>. The insert <NUM> may be formed of a material that is different from the material of each of the leadscrew <NUM> and the nut <NUM>. For example, in one non-limiting example, each of the leadscrew <NUM> and the nut <NUM> may be formed from a metal and the insert <NUM> may be formed from a polymer. In some non-limiting examples, the metallic leadscrew <NUM> and nut <NUM> may be formed from steel (e.g., corrosion resistant or non-corrosion resistant), titanium, copper-based alloys, and the like and the insert <NUM> may be formed from virgin and filled grades of Polyamides, PEEK, PAEK, with fillers being, for example, graphite, carbon, and/or PTFE at various proportions to improve wear performance.

Referring now to <FIG>, a schematic illustration of the leadscrew <NUM> with the insert <NUM> installed thereto is shown and <FIG> illustrates the insert <NUM> in isolation. As shown, the external thread <NUM> of the leadscrew <NUM> forms a generally squared shape for a space <NUM> defined between axially adjacent portions of the external thread <NUM>. The insert <NUM> has a cross-sectional shape that matches or complements the shape of the space <NUM>. As such, in this example, because the space <NUM> has a generally squared shape or geometry, the insert <NUM> has a squared cross-sectional shape, as illustratively shown in <FIG>.

According to the invention, the insert <NUM> is fixedly attached to a specific portion of the leadscrew <NUM>. The attachment of the insert <NUM> to the leadscrew <NUM> may be by known means to enable attaching two different material components. For example, bonding, adhesives, mechanical fixing, or the like may be used to secure the insert <NUM> within the space <NUM> between the external thread <NUM> of the leadscrew <NUM>. In some embodiments, one or more end stops <NUM> may be arranged at ends of the insert <NUM>, as shown in <FIG>. The end stops <NUM> may, in some embodiments, be formed of a material different from the leadscrew <NUM> and the insert <NUM>. For example, the end stops <NUM> may be formed of metallic materials either chemically bonded or mechanically retained within or to the nut. In some embodiments, the end stops <NUM> may be fixedly attached or mounted to the leadscrew <NUM> and the insert <NUM> is not fixedly attached to the leadscrew <NUM>. In such an embodiment, the end stops <NUM> may be used to maintain and hold the insert <NUM> in position relative to either the leadscrew <NUM> or the nut <NUM>.

As described above, the insert <NUM> is attached to the leadscrew <NUM>. However, in other alternative embodiment claimed the insert <NUM> may be fixedly attached to the nut <NUM> and not attached to the leadscrew <NUM>. In some such embodiments, the configuration can include one or more end stops similar to that shown in <FIG>.

Referring back to <FIG>, the insert <NUM> prevents direct material contact between the leadscrew <NUM> and the nut <NUM>. As such, metal-to-metal contact may be avoided. During operation, as the leadscrew <NUM> rotates relative to the nut <NUM>, the insert <NUM> will transfer force between the external threads <NUM> of the leadscrew <NUM> and the internal threads <NUM> of the nut <NUM>. The insert <NUM> may be configured to enable transfer of high loads, such as about <NUM>-<NUM> kN (or about <NUM>-<NUM>,<NUM> lb) and speeds up to <NUM>/s.

Turning now to <FIG>, schematic illustrations of an actuator <NUM> are shown. The actuator <NUM> may be configured for use onboard an aircraft and may be installed and arranged to enable actuation or operation of one or more components, systems, or devices onboard the aircraft. The actuator <NUM> is similar to that shown and described above with respect to <FIG>. For example, the actuator <NUM> includes a leadscrew <NUM> and a nut <NUM>. The leadscrew <NUM> includes an external thread <NUM> and the nut <NUM> includes an internal thread <NUM>. The nut <NUM> is arranged within a housing <NUM>. The leadscrew <NUM> may be operably connected at one or both ends to surfaces and/or structures of an aircraft, with such surface and/or structure, or part thereof, configured to be moved or actuated by linear or axial movement of the leadscrew <NUM> along an axis A.

In operation, the leadscrew <NUM> and the nut <NUM> may be rotated relative to each other to either rotate the nut <NUM> and/or drive axial movement of the leadscrew <NUM>. An insert <NUM> is arranged between the leadscrew <NUM> and the nut <NUM>. The insert <NUM> is configured to fit between the external thread <NUM> of the leadscrew <NUM> and the internal thread <NUM> of the nut <NUM>.

As illustrated in <FIG>, the external thread <NUM> of the leadscrew <NUM> forms a generally rounded or circular shape for a space <NUM> defined between axially adjacent portions of the external thread <NUM>. The insert <NUM> has a cross-sectional shape that matches or complements the shape of the space <NUM>. As such, in this example, because the space <NUM> has a generally circular shape or geometry, the insert <NUM> has a circular cross-sectional shape, as illustratively shown in <FIG>. In this configuration, in contrast to the embodiment of <FIG>, no end stops are included. The insert <NUM> may be fixedly attached (e.g., bonded or otherwise attached) to the leadscrew <NUM> or the nut <NUM>, depending on the specific configuration to be implemented. Due to the direct attachment between the insert <NUM> and the other component, the end stops may be omitted.

Referring now to <FIG>, schematic illustrations of a portion of an actuator <NUM> are shown. The actuator <NUM> includes a nut <NUM> with an insert <NUM> installed thereto. As shown, insert <NUM> is installed into a thread <NUM> of the nut <NUM>. In this configuration, the insert <NUM> is a two-start insert coil, having a first start <NUM> and a second start <NUM>. As a result of the two-start insert coil, the insert <NUM> may be formed of two separate windings to accommodate the threads <NUM> (or configuration thereof) of the nut <NUM>. The insert <NUM> may be fixedly attached to the nut <NUM> by adhesive bonding <NUM>, similar to that described above. Further, the insert <NUM> may be retained and positioned within the threads <NUM> of the nut <NUM> by one or more mechanisms, including the adhesive bonding <NUM>. Such additional retention and positioning features may include, for example, a grub screw installed tangential to helical coil/insert and/or inserts placed at the ends of the insert <NUM>. In some such configurations, the nut <NUM> can include a cut outs with the inserts placed into the cutouts by approaching from either inside or outside and retained by a cylinder and screw shaft.

The inserts of the present invention may be machined or molded. As the inserts are installed about or within a thread of a leadscrew or nut, the inserts will have a helical structure having a defined cross-sectional shape/geometry to match or complement the thread. When placed between metallic nuts and leadscrews the inserts will prevent metal to metal contact. In the invention, the insert is held captive within the nut (e.g., by mechanical or bonding methods). This captive retention can prevent the inserts from winding out during actuation of the leadscrew. In some embodiments, multiple inserts may be arranged in sequence about the threads of the nut or leadscrew. This configuration can lead to a multi-start insert configuration that enables distribution or sharing of loads carried by the insert, thus increasing the overall load capability of the actuator.

Advantageously, the inserts for actuators described herein enable extending the benefit of a polymeric nut to higher load applications by using a polymeric insert arranged between metallic components (e.g., leadscrew and nut). The inserts may be formed to tailor a flank width to reduce contact pressures, which in turn can result in lower pressure-velocity ("pv"). The inserts described can achieve longevity of actuators due to low wear behavior of the insert and avoidance of metal-to-metal contact/wear between threads of a leadscrew and a nut of the actuator.

The use of the terms "a", "an", "the", and similar references in the context of description (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifiers or terms "about" and/or "substantially" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. As used herein, 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, the terms may include a range of ± <NUM>%, or <NUM>%, or <NUM>% of a given value or other percentage change as will be appreciated by those of skill in the art for the particular measurement and/or dimensions referred to herein.

Claim 1:
A leadscrew and nut actuator comprising:
a leadscrew (<NUM>) having an external thread (<NUM>) and formed from a first material;
a nut (<NUM>) configured to receive the leadscrew (<NUM>), the nut (<NUM>) having an internal thread (<NUM>) and formed from a second material; and
an insert (<NUM>, <NUM>, <NUM>) arranged between the internal thread (<NUM>) of the nut (<NUM>) and the external thread (<NUM>) of the leadscrew (<NUM>), the insert (<NUM>, <NUM>, <NUM>) configured to transfer force between the external thread (<NUM>) and the internal thread (<NUM>) and prevent material contact between the leadscrew (<NUM>) and the nut (<NUM>),
wherein the insert (<NUM>, <NUM>, <NUM>) is formed of a third material different from the first material and the second material,
characterized by either
at least one end stop (<NUM>) fixedly attached to the leadscrew (<NUM>) and arranged within a space between axially adjacent portions of the external thread (<NUM>) and configured to retain a position of the insert (<NUM>, <NUM>, <NUM>) relative to the leadscrew (<NUM>),
or
at least one end stop (<NUM>) fixedly attached to the nut (<NUM>) and arranged within a space between axially adjacent portions of the internal thread (<NUM>) and configured to retain the position of the insert (<NUM>, <NUM>, <NUM>) relative to the nut (<NUM>.