Patent Description:
Shape memory alloy actuators are solid state actuators that may be utilized to provide a motive force for motion of one object, such as an attached component, relative to another object, such as a base structure to which the attached component is attached via the shape memory alloy actuator. Shape memory alloy actuators may generate the motive force via a phase change within a shape memory alloy element thereof, and this phase change may be initiated by a temperature change. As an example, the shape memory alloy element may transition from a martensite state to an austenite state upon being heated and also may transition from the austenite state to the martensite state upon being cooled.

Heating of the shape memory alloy element historically has been accomplished utilizing a heating assembly, such as a resistive heating element and/or an inductive heating element. In contrast, cooling of the shape memory alloy element historically has been accomplished via convective cooling with a heat transfer fluid stream. The heating generally may be performed relatively quickly; however, the cooling often takes a significantly longer amount of time and thus may be rate-limiting to an overall cycle time of the shape memory alloy actuator (e.g., a time needed to transition the shape memory alloy element from the martensite state to the austenite state and back to the martensite state or vice versa).

In general, a rate of convective cooling may be increased by increasing a surface area for heat transfer between a body to be cooled and a heat transfer fluid stream that flows in fluid contact with the body to be cooled. As an example, cooling fins may be affixed to the body to be cooled and/or may be defined by the body to be cooled.

While such an approach may be effective under certain circumstances, it may be difficult, or even impossible, to effectively and reliably implement in the context of a shape memory alloy element. As an example, the shape memory alloy element may experience significant physical deformation upon transitioning between the martensite state and the austenite state, and this physical deformation may make it difficult, or even impossible, to operatively attach cooling fins to the shape memory alloy element. As another example, a shape memory alloy that defines the shape memory alloy element may have a low thermal conductivity, and cooling fins that might be defined by the shape memory alloy element itself may not be effective at improving convective cooling of the shape memory alloy element. Thus, there exists a need for improved shape memory alloy actuators with heat transfer structures, for actuated assemblies that include the improved shape memory alloy actuators, and/or for methods of manufacturing the improved shape memory alloy actuators.

<CIT>, in accordance with its abstract, states an SMA actuator that includes a cooling device disposed within a torque tube. In one aspect, the cooling device includes a sliding sleeve, an expandable sleeve, and plurality of cooling fins coupled to the expandable sleeve. Axial movement of the sliding sleeve relative to the expandable sleeve facilitates radial expansion of the expandable sleeve and urges the cooling fins into contact with the torque tube. The cooling fins function as heat sinks when in contact with the torque tube to facilitate the removal of heat from the torque tube to increase the cooling rate of the torque tube. During heating of the torque tube, the cooling fins may be spaced apart from the torque tube to reduce the thermal mass that is heated, thus increasing the heating rate of the torque tube.

<CIT>, in accordance with its abstract, states a system for heating a shape memory alloy (SMA) actuator which include an SMA actuator, a smart susceptor, a plurality of induction coils, and a control module. The SMA actuator may have at least one layup. The SMA actuator may be selectively heated to a transition temperature. The smart susceptor may be in thermal contact with the at least one layup of the SMA actuator. The induction heating coils may be configured to receive an alternating current and generate a magnetic field based on the alternating current. The magnetic field may create an eddy current in at least one of the SMA actuator and the smart susceptor to heat the SMA actuator to the transition temperature. The control module may be configured to drive the alternating current supplied to the induction heating coils.

<CIT>, in accordance with its abstract, states a rotary actuator includes a bar made of shape memory alloy having ends provided with thermally insulating interface elements for interfacing with elements that are to be rotated relative to each other. An electric heater surrounds the bar and is apt to heat it above its transition temperature to the austenitic domain. The actuator is suitable for deploying or rotating solar panels.

<CIT>, in accordance with its abstract, states a rotary actuator including an actuator assembly. The actuator assembly includes a torque tube formed of a shape memory alloy, a super elastic NiTinol return spring having a proximal end and a distal end, and a torque tube heating element positioned near the torque tube. The torque tube includes a proximal end and a distal end. The return spring and torque tube are connected at their ends, with the torque tube being pretwisted while in a martensitic state relative to the spring. Activation of the heating element causes the torque tube to enter an austenitic state in which it returns to its previous untwisted configuration. Removal of heat allows the torque tube to return to a martensitic state, further allowing the return spring to retwist the torque tube. Further provided is a unique locking assembly for use with the actuator assembly. Further provided is a helicopter blade twist rotation system for use with a rotor craft blade having a blade root and a tip. The system includes a shape memory alloy rotary actuator located within the blade near the blade root, and a passive torque tube located within the blade and having a proximal end connected to the rotary actuator and a distal end connected to the blade near to the blade tip.

<CIT>, in accordance with its abstract, states an elongate medical device including an inner elongate member, a reinforcing member, and an outer tubular member is described. The reinforcing member may be a helically wound continuous wire including a first portion having a first cross-sectional profile, a second portion having a second cross-sectional profile, and a transition region located between the first portion and the second portion. The first cross-sectional profile may be different from the second cross-sectional profile. In some embodiments, the first cross-sectional profile may be circular or non-circular and the second cross-sectional profile may be circular or non-circular.

Shape memory alloy actuators with heat transfer structures, and methods of manufacturing the same are disclosed herein, as defined in the appended claims.

A shape memory alloy (SMA) actuator according to the present disclosure is defined in appended claim <NUM>, and includes a shape memory alloy torque tube and a heat transfer structure. The shape memory alloy torque tube has a first end, a second end, and an elongate surface extending between the first end and the second end. The heat transfer structure is in mechanical and thermal contact with the elongate surface of the SMA torque tube and extends at least partially between the first end and the second end of the SMA torque tube. The heat transfer structure also exerts a retention force on the SMA torque tube that retains the heat transfer structure in mechanical and thermal contact with the elongate surface of the SMA torque tube.

A method according to the present disclosure of manufacturing said shape memory alloy actuator is defined in appended claim <NUM>, and includes providing a shape memory alloy torque tube, providing a heat transfer structure, applying a dimension-modifying force to the heat transfer structure, combining the heat transfer structure with the shape memory alloy torque tube, and releasing the dimension-modifying force. The applying the dimension-modifying force may include applying to place the heat transfer structure in a modified-dimensional conformation such that a modified characteristic dimension of the heat transfer structure differs from a natural characteristic dimension of the heat transfer structure prior to application of the dimension-modifying force. The combining includes combining such that the heat transfer structure extends at least partially between a first end and a second end of the SMA torque tube. The releasing includes releasing such that the heat transfer structure exerts a retention force on an elongate surface of the SMA torque tube.

<FIG> provide illustrative, non-exclusive examples of shape memory alloy actuators <NUM>, according to the present disclosure, some being claimed herein and others not, of actuated assemblies <NUM> including shape memory alloy actuators <NUM>, and/or of methods <NUM>, of manufacturing shape memory alloy actuators, such as shape memory alloy actuators <NUM>. Elements that serve a similar, or at least substantially similar, purpose are labeled with like numbers in each of <FIG>, and these elements may not be discussed in detail herein with reference to each of <FIG>. Similarly, all elements may not be labeled in each of <FIG>, but reference numerals associated therewith may be utilized herein for consistency. Elements, components, and/or features that are discussed herein with reference to one or more of <FIG> may be included in and/or utilized with any of <FIG>.

In general, elements that are likely to be included in a given (i.e., a particular) example are illustrated in solid lines, while elements that are optional to a given example are illustrated in dashed lines. However, elements that are shown in solid lines are not essential to all examples, and an element shown in solid lines may be omitted from a particular example.

<FIG> is a schematic representation illustrating examples of an actuated assembly <NUM> including a shape memory alloy (SMA) actuator <NUM>, according to the present disclosure, although not claimed herein. As illustrated in solid lines in <FIG>, actuated assembly <NUM> includes a base structure <NUM>, an attached component <NUM>, and SMA actuator <NUM>. As also illustrated in <FIG>, attached component <NUM> is operatively attached to base structure <NUM> via and/or utilizing SMA actuator <NUM> and such that actuation of SMA actuator <NUM> produces and/or generates relative motion between base structure <NUM> and attached component <NUM>. This is illustrated schematically in <FIG> by attached component <NUM> transitioning from a first, or an initial, orientation relative to base structure <NUM>, as illustrated in solid lines, to a second, or subsequent, orientation relative to base structure <NUM>, as illustrated in dash-dot lines.

The SMA actuator <NUM> may produce, generate, regulate, and/or control any suitable motion, or relative motion, between base structure <NUM> and attached component <NUM>. As examples, SMA actuator <NUM> may produce, generate, regulate, control, and/or provide a motive force for one or more of rotary relative motion, linear relative motion, translational relative motion, and/or arcuate relative motion between base structure <NUM> and attached component <NUM>. As a more specific example, and as discussed in more detail herein with reference to <FIG>, SMA actuator <NUM> includes a shape memory alloy torque tube <NUM> that has an elongate surface and is configured to produce, generate, regulate, control, and/or provide a motive force for rotary relative motion between base structure <NUM> and attached component <NUM>. As also discussed in more detail herein with reference to <FIG>, SMA actuator <NUM> includes a heat transfer structure <NUM> that is in mechanical and thermal contact with the elongate surface of SMA torque tube <NUM>.

During operation of actuated assemblies <NUM> including SMA actuators <NUM>, according to the present disclosure, a temperature of SMA torque tube <NUM> may be changed, thereby causing shape memory alloy torque tube <NUM> to deform and to generate, or to provide the motive force for, relative motion between the base structure and the attached component. As an example, SMA torque tube <NUM> may be heated, thereby causing SMA torque tube <NUM> to deform and/or to transition from a martensite state to an austenite state and causing attached component <NUM> to transition from the orientation that is illustrated in solid lines in <FIG> to the orientation that is illustrated in dash-dot lines. As another example, SMA torque tube <NUM> may be cooled, thereby causing SMA torque tube <NUM> to deform and/or to transition from the austenite state to the martensite state and causing attached component <NUM> to transition from the orientation that is illustrated in dash-dot lines in <FIG> to the orientation that is illustrated in solid lines. This process may be repeated any suitable number of times to produce and/or generate any suitable number of relative orientation transitions between base structure <NUM> and attached component <NUM>.

Heat transfer structure <NUM> may improve, or increase, heat transfer to and/or from the SMA torque tube, thereby increasing a rate at which the SMA torque tube may be transitioned from the martensite state to the austenite state and/or from the austenite state to the martensite state. In addition, and as discussed in more detail herein with reference to <FIG> and <FIG>, heat transfer structure <NUM> exerts a retention force <NUM> on SMA torque tube <NUM>, and retention force <NUM> retains heat transfer structure <NUM> in mechanical and thermal contact with SMA torque tube <NUM>. Retention force <NUM> may retain heat transfer structure <NUM> in mechanical and thermal contact with SMA torque tube <NUM> despite deformation of SMA torque tube <NUM> and/or despite relative motion, or even sliding, between a portion of SMA torque tube <NUM> and a portion of heat transfer structure <NUM>.

As illustrated in dashed lines in <FIG>, actuated assembly <NUM> also may include a thermal control assembly <NUM>. Thermal control assembly <NUM>, when present, may be configured to control, regulate, and/or specify a temperature of SMA torque tube <NUM>, thereby controlling, regulating, and/or specifying a state of SMA torque tube <NUM>, a deformation of SMA torque tube <NUM>, and/or a relative orientation between base structure <NUM> and attached component <NUM>.

Thermal control assembly <NUM> may include any suitable structure and/or structures. As an example, thermal control assembly <NUM> may include a heating assembly <NUM>. Heating assembly <NUM>, when present, may be configured to heat SMA torque tube <NUM>, to increase a temperature of SMA torque tube <NUM>, and/or to cause SMA torque tube <NUM> to transition from the martensite state to the austenite state. Examples of heating assembly <NUM> include any suitable electric heater, resistive heater, and/or inductive heater.

As another example, thermal control assembly <NUM> additionally or alternatively may include a cooling assembly <NUM>. Cooling assembly <NUM>, when present, may be configured to cool SMA torque tube <NUM>, to decrease a temperature of SMA torque tube <NUM>, and/or to transition SMA torque tube <NUM> from the austenite state to the martensite state. Examples of cooling assembly <NUM> include any suitable convective cooling assembly, conductive cooling assembly, radiative cooling assembly, air conditioning system, solid state cooling assembly, and/or piezoelectric device.

As yet another example, thermal control assembly <NUM> additionally or alternatively may include a fluid propulsion system <NUM>. Fluid propulsion system <NUM> may be configured to direct a heat transfer fluid stream in thermal contact with the elongate surface of SMA torque tube <NUM> and/or with heat transfer structure <NUM>, and it is within the scope of the present disclosure that the heat transfer fluid stream may be utilized to heat and/or to cool SMA torque tube <NUM>. Under these conditions, heating assembly <NUM> may be utilized to heat the heat transfer fluid stream and/or cooling assembly <NUM> may be utilized to cool the heat transfer fluid stream prior to fluid contact between the heat transfer fluid stream and the elongate surface of SMA torque tube <NUM> and/or prior to fluid contact between the heat transfer fluid stream and heat transfer structure <NUM>.

With this in mind, <FIG> illustrates fluid propulsion system <NUM> as optionally being included in, forming a portion of, and/or being utilized in conjunction with heating assembly <NUM> and/or cooling assembly <NUM>. In addition, and as discussed in more detail herein, heat transfer structure <NUM> may be adapted, configured, designed, sized, shaped, and/or constructed to increase heat transfer between SMA torque tube <NUM> and the heat transfer fluid stream when compared to prior art shape memory alloy actuators that do not include, or utilize, heat transfer structure <NUM>.

As a more specific but still illustrative, non-exclusive example, thermal control assembly <NUM> may include heating assembly <NUM> in the form of an inductive heater, which may be configured to inductively heat SMA torque tube <NUM>. In addition, thermal control assembly <NUM> also may include cooling assembly <NUM> in the form of fluid propulsion system <NUM>, which may be configured to cool SMA torque tube <NUM> by flowing the heat transfer fluid stream in fluid contact with the elongate surface of SMA torque tube <NUM> and also in fluid contact with heat transfer structure <NUM>.

Examples of fluid propulsion system <NUM> include any suitable fan, compressor, blower, pump, and/or air inlet that controls and/or regulates flow of the heat transfer fluid stream in thermal contact with the elongate surface of SMA torque tube <NUM> and/or with heat transfer structure <NUM>. Examples of the heat transfer fluid stream include a thermally conductive fluid, a refrigerant, a liquid, a gas, and/or air.

Base structure <NUM> may include any suitable structure that may be operatively attached to, or may support, SMA actuator <NUM> and/or attached component <NUM>. As examples, base structure <NUM> may include one or more of an aircraft, an airplane, and/or a helicopter. Similarly, attached component <NUM> may include any suitable structure that may be operatively attached to base structure <NUM> via SMA actuator <NUM> and/or that may be moved relative to base structure <NUM> via actuation of SMA actuator <NUM>. As examples, attached component <NUM> may include one or more of an actuated component, a landing gear, a flap, an aileron, and/or a rotor.

<FIG> is a more detailed but still schematic longitudinal cross-sectional view of a shape memory alloy actuator <NUM>, such as shape memory alloy actuator <NUM> of <FIG>, taken along line <NUM>-<NUM> of <FIG>, while <FIG> is a more detailed but still schematic transverse cross-sectional view of SMA actuator <NUM> taken along line <NUM>-<NUM> of <FIG>. As illustrated collectively by <FIG> in an example not claimed herein, SMA actuator <NUM> includes SMA torque tube <NUM> that defines a first end <NUM>, a second end <NUM>, and an elongate surface <NUM> that extends between first end <NUM> and second end <NUM>. Elongate surface <NUM> is illustrated in dashed lines to indicate that elongate surface <NUM> can include, or be, an inner surface <NUM> of SMA torque tube <NUM> and/or an outer surface <NUM> of SMA torque tube <NUM>.

SMA actuator <NUM> also includes heat transfer structure <NUM>. Heat transfer structure <NUM> is in both mechanical and thermal contact with elongate surface <NUM> of SMA torque tube <NUM> and extends at least partially between first end <NUM> and second end <NUM> of SMA torque tube <NUM>. In addition, and as illustrated in <FIG> and <FIG>, heat transfer structure <NUM> exerts retention force <NUM> on SMA torque tube <NUM>, and retention force <NUM> retains heat transfer structure <NUM> in both mechanical and thermal contact with elongate surface <NUM> of SMA torque tube <NUM>. Heat transfer structure <NUM> also may be referred to herein as being, or may be, in electrical contact, or in direct electrical contact, with elongate surface <NUM> of SMA torque tube <NUM>.

Heat transfer structure <NUM> may exert and/or generate retention force <NUM> in any suitable manner. As an example, retention force <NUM> may include, or be, a restoring force that is generated by heat transfer structure <NUM>.

As a more specific example not claimed herein and as illustrated in dash-dot lines in <FIG>, heat transfer structure <NUM> may be in mechanical and thermal contact with inner surface <NUM> of SMA torque tube <NUM>. Stated another way, elongate surface <NUM> may include, or be, inner surface <NUM>. As such, retention force <NUM> may extend outward from, generally outward from, or away from, a longitudinal axis <NUM> of SMA torque tube <NUM>. Under these conditions, heat transfer structure <NUM> may define an uncompressed, or an average uncompressed, outer dimension <NUM>, which is measured prior to heat transfer structure <NUM> being combined with SMA torque tube <NUM> to define SMA actuator <NUM> (illustrated in solid lines in <FIG>), and a compressed, or an average compressed, outer dimension <NUM>, which is measured subsequent to heat transfer structure <NUM> being combined with SMA torque tube <NUM> to define SMA actuator <NUM> (illustrated in dash-dot lines in <FIG>). Uncompressed outer dimension <NUM> may be greater than compressed outer dimension <NUM>, thereby causing heat transfer structure <NUM> to exert retention force <NUM>, in the form of the restoring force, on inner surface <NUM> of SMA torque tube <NUM>.

As another more specific example not claimed herein and as illustrated in dash-dot lines in <FIG>, heat transfer structure <NUM> may be in mechanical and thermal contact with outer surface <NUM> of SMA torque tube <NUM>. Stated another way, elongate surface <NUM> may include, or be, outer surface <NUM>. As such, retention force <NUM> may extend inward toward, generally inward toward, or toward, longitudinal axis <NUM> of SMA torque tube <NUM>. Under these conditions, heat transfer structure <NUM> may define an unexpanded, or an average unexpanded, inner dimension <NUM>, which is measured prior to heat transfer structure <NUM> being combined with SMA torque tube <NUM> to define SMA actuator <NUM> (illustrated in solid lines in <FIG>), and an expanded, or an average expanded, inner dimension <NUM>, which is measured subsequent to heat transfer structure <NUM> being combined with SMA torque tube <NUM> to define SMA actuator <NUM> (illustrated in dash-dot lines in <FIG>). Unexpanded inner dimension <NUM> may be less than expanded inner dimension <NUM>, thereby causing heat transfer structure <NUM> to exert retention force <NUM> on outer surface <NUM> of SMA torque tube <NUM>.

The heat transfer structure <NUM> may be retained in mechanical and thermal contact with SMA torque tube <NUM> solely by retention force <NUM>. Additionally or alternatively, heat transfer structure <NUM> may be retained in mechanical and thermal contact with SMA torque tube <NUM> solely by retention force <NUM>. This may include being retained in mechanical and thermal contact with SMA torque tube <NUM> over at least a threshold fraction of a length <NUM> (as illustrated in <FIG>) of heat transfer structure <NUM>. Examples of the threshold fraction of length <NUM> include at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>% at least <NUM>%, at least <NUM>%, at least <NUM>%, and/or <NUM>% of length <NUM>. Additionally or alternatively, the threshold fraction of length <NUM> may be at most <NUM>%, at most <NUM>%, at most <NUM>%, at most <NUM>%, or at most <NUM>% of length <NUM>.

Heat transfer structure <NUM> may have and/or define any suitable shape and may have, may define, and/or may be shaped to define, a surface area for heat transfer between SMA torque tube <NUM> and a heat transfer fluid stream that flows in fluid contact therewith. As an example, and as illustrated in <FIG>, heat transfer structure <NUM> may be helically shaped, at least partially helically shaped, coil-shaped, at least partially coil-shaped, spiral-shaped, at least partially spiral-shaped, arcuate, and/or at least partially arcuate. As another example not claimed herein and as illustrated schematically in <FIG> and less schematically in <FIG>, heat transfer structure <NUM> may include at least one, or even a plurality of, surface-contacting regions <NUM> that mechanically and thermally contact elongate surface <NUM> of SMA torque tube <NUM> and apply retention force <NUM> to SMA torque tube <NUM>. In addition, heat transfer structure <NUM> also may include a plurality of projecting regions <NUM> that project from, or away from, elongate surface <NUM>. This may include projecting away from elongate surface <NUM> at any suitable angle. As an example, projecting regions <NUM> may project perpendicular, or at least substantially perpendicular, to elongate surface <NUM>.

When heat transfer structure <NUM> includes the plurality of surface-contacting regions <NUM> and the plurality of projecting regions <NUM>, each surface-contacting region <NUM> may be spaced apart from an adjacent surface-contacting region <NUM> by a corresponding projecting region <NUM>, as illustrated in <FIG>. Additionally or alternatively, the plurality of surface-contacting regions <NUM> may form a continuous, or at least substantially continuous, surface-contacting region <NUM>, as illustrated in <FIG>.

As illustrated schematically in <FIG> and less schematically in <FIG>, <FIG>, heat transfer structure <NUM> may include, be, and/or be at least partially defined by an elongate conductive body <NUM>. It is within the scope of the present disclosure that elongate conductive body <NUM> may define, or may be shaped to define, both surface-contacting regions <NUM> and projecting regions <NUM>, as illustrated in <FIG>. Under these conditions, elongate conductive body <NUM> may have, or define, a body length, and elongate conductive body <NUM> may be in mechanical and thermal contact with elongate surface <NUM> of SMA torque tube <NUM> over a fraction of the body length. As examples, the fraction of the body length may be at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, and/or at least <NUM>% of the body length. Additionally or alternatively, the fraction of the body length may be at most <NUM>%, at most <NUM>%, at most <NUM>%, at most <NUM>%, at most <NUM>%, or at most <NUM>% of the body length.

Additionally or alternatively, at least a subset, or fraction, of the plurality of projecting regions <NUM>, when present, may be operatively attached to elongate conductive body <NUM>, as illustrated in <FIG>. As an example, projecting regions <NUM> may be adhered, brazed, and/or welded to elongate conductive body <NUM>.

Turning now more specifically to <FIG>, an embodiment of a shape memory alloy actuator <NUM>, as claimed herein, is illustrated in which an elongate conductive body <NUM> forms and/or defines an entirety of heat transfer structure <NUM>. Elongate conductive body <NUM> includes a plurality of helical, or at least substantially helical, regions, which are in mechanical and thermal contact with elongate surface <NUM> of SMA torque tube <NUM> and define surface-contacting regions <NUM>. In addition, elongate conductive body <NUM> also includes a plurality of deviation regions, which deviate from a helical shape and project away from elongate surface <NUM> to define projecting regions <NUM>. As illustrated, a corresponding deviation (i.e., projecting region <NUM>) extends between each adjacent pair of helical regions (i.e., surface-contacting regions <NUM>).

The heat transfer structure <NUM> may have and/or define any suitable cross-sectional shape, or transverse cross-sectional shape. As an example, and as illustrated in <FIG> and <FIG>, heat transfer structure <NUM> may include one or more subtraction regions <NUM>, which also may be referred to herein as void spaces <NUM>, machined regions <NUM>, and/or subtractively machined regions <NUM>. Such subtraction regions <NUM> may increase a surface area of heat transfer structure <NUM>, thereby improving convective heat transfer between heat transfer structure <NUM> and the heat transfer fluid stream.

As another example, heat transfer structure <NUM> may be shaped such that a surface of heat transfer structure <NUM> that is in mechanical and thermal contact with elongate surface <NUM> of SMA torque tube <NUM> may be in face-to-face, or at least partial face-to-face, contact with elongate surface <NUM>. This is illustrated in <FIG>, which is a less schematic transverse cross-sectional view of an example of an elongate conductive body <NUM> that defines a heat transfer structure <NUM> according to the present disclosure. As illustrated therein, heat transfer structure <NUM> may define a conductive heat transfer surface <NUM> and a convective heat transfer surface <NUM>. Conductive heat transfer surface <NUM> may be shaped to mechanically and thermally contact elongate surface <NUM> of SMA torque tube <NUM>, while convective heat transfer surface <NUM> may be shaped for heat transfer with the heat transfer fluid stream. As an example, and as illustrated, a transverse cross-section of conductive heat transfer surface <NUM> may be linear, or at least substantially linear. In contrast, and as also illustrated, a transverse cross-section of convective heat transfer surface <NUM> may be nonlinear, arcuate, partially circular, partially elliptical, and/or D-shaped. Additionally or alternatively, a radius of curvature of conductive heat transfer surface <NUM> may be greater than a radius of curvature of convective heat transfer surface <NUM>, and both radii of curvature may be measured in the transverse cross-section of elongate conductive body <NUM>.

Heat transfer structure <NUM> may be formed from and/or defined by any suitable heat transfer material, and the heat transfer material may be different from a shape memory alloy that defines SMA torque tube <NUM>. As an example, the heat transfer material may have a greater thermal conductivity than the shape memory alloy. As another example, the heat transfer material may have a greater stiffness than the shape memory alloy. As yet another example, the heat transfer material may have a greater electronegativity than the shape memory alloy such that the heat transfer material functions as a sacrificial anode for the shape memory alloy.

Examples of the heat transfer material include a resilient material, aluminum, an aluminum alloy, copper, a copper alloy, brass, and red brass. Examples of the shape memory alloy include a binary alloy, a nickel-titanium alloy, a binary nickel-titanium alloy, a ternary alloy, a ternary alloy that includes nickel and titanium and further includes hafnium, copper, iron, silver, cobalt, chromium, vanadium, and/or a quaternary alloy.

As examples, SMA torque tube <NUM> may be tubular and/or cylindrical. As another example, SMA torque tube <NUM> may be a hollow SMA torque tube and heat transfer structure <NUM> may extend therein. As yet another example, SMA torque tube <NUM> may define both inner surface <NUM> and outer surface <NUM>, which are discussed herein.

Returning to <FIG>, shape memory alloy actuators <NUM>, according to the present disclosure although not claimed herein, also may include a thermal sensor <NUM>. Thermal sensor <NUM>, when present, may be configured to detect a temperature of SMA torque tube <NUM>. In addition, thermal sensor <NUM> may be operatively attached to heat transfer structure <NUM> and/or may be pressed into mechanical and thermal contact with SMA torque tube <NUM> via and/or utilizing heat transfer structure <NUM>. Under these conditions, thermal sensor <NUM> may not be, or may not be required to be, adhered and/or affixed to a specific region of SMA torque tube <NUM>. Examples of thermal sensor <NUM> include a thermocouple, a thermistor, and/or a resistance temperature detector (RTD).

<FIG> is a flowchart depicting methods <NUM>, according to the present disclosure, of manufacturing a shape memory alloy actuator, such as shape memory alloy actuator <NUM> of <FIG>. Methods <NUM> include providing a shape memory alloy (SMA) torque tube at <NUM>, providing a heat transfer structure at <NUM>, applying a dimension-modifying force at <NUM>, combining the SMA torque tube and the heat transfer structure at <NUM>, and releasing the dimension-modifying force at <NUM>.

Providing the shape memory alloy (SMA) torque tube at <NUM> may include providing any suitable SMA torque tube, examples of which are discussed herein with reference to SMA torque tube <NUM>. The SMA torque tube may have and/or define a first end, a second end, and an elongate surface that extends between the first end and the second end. The providing at <NUM> may include providing in any suitable manner. As examples, the providing at <NUM> may include purchasing, obtaining, ordering, and/or fabricating the SMA torque tube.

Providing the heat transfer structure at <NUM> may include providing any suitable heat transfer structure, examples of which are discussed herein with reference to heat transfer structure <NUM>. The providing at <NUM> may include providing in any suitable manner. As examples, the providing at <NUM> may include purchasing, obtaining, ordering, and/or fabricating the heat transfer structure.

Applying the dimension-modifying force at <NUM> may include applying any suitable dimension-modifying force to the heat transfer structure, and application of the dimension-modifying force may permit and/or facilitate the combining at <NUM>. As an example, the applying at <NUM> may include applying the dimension-modifying force to place the heat-transfer structure in a modified-dimensional conformation such that a modified characteristic dimension of the heat transfer structure differs from a natural, or unmodified, characteristic dimension of the heat transfer structure that may be exhibited by the heat transfer structure prior to application of the dimension-modifying force to the heat transfer structure. As examples, the applying at <NUM> may include twisting the heat transfer structure, as indicated at <NUM>, compressing the heat transfer structure, as indicated at <NUM>, and/or expanding the heat transfer structure, as indicated at <NUM>.

Combining the SMA torque tube and the heat transfer structure at <NUM> may include combining such that the heat transfer structure extends at least partially between the first end of the SMA torque tube and the second end of the SMA torque tube and/or combining such that the heat transfer structure extends along, in contact with, and/or parallel to the elongate surface of the SMA torque tube. As an example, the elongate surface of the SMA torque tube may include, or be, an inner surface of the SMA torque tube. Under these conditions, the applying at <NUM> may include the twisting at <NUM> and/or the compressing at <NUM>, such that the modified characteristic dimension is less than the natural characteristic dimension, and the combining at <NUM> may include inserting the heat transfer structure within the SMA torque tube, as indicated at <NUM>. As another example, the elongate surface of the SMA torque tube may include, or be, an outer surface of the SMA torque tube. Under these conditions, the applying at <NUM> may include the twisting at <NUM> and/or the expanding at <NUM>, such that the modified characteristic dimension is greater than the natural characteristic dimension, and the combining at <NUM> may include extending the heat transfer structure around, or about, the SMA torque tube, as indicated at <NUM>.

Releasing the dimension-modifying force at <NUM> may include releasing the dimension-modifying force such that the heat transfer structure transitions to an intermediate conformation in which an intermediate characteristic dimension of the heat transfer is between the modified characteristic dimension and the natural characteristic dimension. Under these conditions, the heat transfer structure may exert a restoring force, which may tend to return the heat transfer structure to the natural characteristic dimension, and this restoring force may cause the heat transfer structure to exert a retention force on the elongate surface of the SMA torque tube. This retention force may retain the heat transfer structure in mechanical and thermal contact with the elongate surface of the SMA torque tube.

As used herein, the terms "selective" and "selectively," when modifying an action, movement, configuration, or other activity of one or more components or characteristics of an apparatus, mean that the specific action, movement, configuration, or other activity is a direct or indirect result of user manipulation of an aspect of, or one or more components of, the apparatus.

Claim 1:
A shape memory alloy actuator (<NUM>), comprising:
a shape memory alloy (SMA) torque tube (<NUM>) having a first end (<NUM>), a second end (<NUM>), and an elongate surface (<NUM>) extending between the first end and the second end; and
a heat transfer structure (<NUM>), wherein the heat transfer structure:
(i) is in mechanical and thermal contact with the elongate surface of the SMA torque tube;
(ii) extends at least partially between the first end and the second end of the SMA torque tube; and
(iii) has a natural characteristic dimension and a modified characteristic dimension, and an intermediate conformation in which an intermediate characteristic dimension of the heat transfer structure (<NUM>) is between the modified characteristic dimension and the natural characteristic dimension, wherein the heat transfer structure (<NUM>) exerts a retention force (<NUM>) on the SMA torque tube in said intermediate conformation so that the heat transfer structure (<NUM>) is retained in mechanical and thermal contact with the elongate surface of the SMA torque tube solely by said retention force (<NUM>),
characterized in that the heat transfer structure (<NUM>) includes an elongate conductive body (<NUM>), wherein the elongate conductive body (<NUM>) has:
a plurality of helical surface-contacting regions (<NUM>) that are in mechanical and thermal contact with the elongate surface (<NUM>) of the SMA torque tube (<NUM>), and
a plurality of deviation regions (<NUM>) that deviate from a helical shape and project away from the elongate surface (<NUM>) of the SMA torque tube (<NUM>), wherein a corresponding deviation region (<NUM>) of the plurality of deviation regions (<NUM>) extends between each adjacent pair of surface-contacting regions (<NUM>) of the plurality of surface-contacting regions (<NUM>).