Shape memory alloy actuator subassembly with magnetic element and fluid valve comprising the same

Abstract

The invention relates in a first aspect to an actuator sub-assembly comprising a shape memory alloy wire (15), a biasing spring (16) and a magnetically responsive element (17, 17') to couple the motion of a first movable element (13) and a second movable element (14) having a terminal (18), and in a second aspect to a fluid valve comprising a plunger, the terminal portion of which controls its opening and closing, and wherein the plunger motion is controlled by the action of a shape memory alloy wire, a biasing element and a magnetically responsive element.

Description

Technical Field

[0001] The invention relates in a first aspect to an actuator subassembly comprising a shape memory alloy (SMA) wire and a magnetically coupled movable element for moving the element together with a terminal portion. Background Technology

[0002] Actuator assemblies and actuation systems employing shape memory alloy wires are known in the art and are becoming increasingly popular due to recent developments that have improved their reliability and robustness, allowing full utilization of their inherent advantages such as compactness and ease of integration. For example, International Patent Application WO2016 / 156283, filed by the applicant, relates to locks with emergency actuators; European Patent 2615951, filed by the applicant, describes an actuation system for valves installed in multi-drink vending machines; European Patent 2171183, filed by the applicant, describes actuators with a wider operating temperature range; and International Patent Application WO2015 / 150377 describes actuation elements in household appliances.

[0003] All these devices utilize the characteristics of shape memory alloys (SMAs). More specifically, SMA materials are characterized by structural transformations between two phases—a so-called martensitic phase stable at a lower temperature and a so-called austenitic phase stable at a higher temperature. Shape memory alloys are characterized by four temperatures: Mf, Ms, As, and Af. Mf is the temperature below which the shape memory alloy is entirely in the martensitic phase, i.e., it has a martensitic structure. Af is the temperature above which the shape memory alloy is entirely in the austenitic phase, i.e., it has an austenitic structure. Ms and As are the temperatures at which the martensitic and austenitic transformations begin, respectively.

[0004] When the temperature changes from below Mf to above Af and from above Af to below Mf, the shape of a wire made of shape memory alloy—also known as SMA wire—can be changed by training it. The handling and training of SMA wire is a well-known process in the art, as illustrated in the paper "(Shape Memory Alloy Shape Training Tutorial)" from the training section of "ME559 – Smart Materials and Structures" dating back to the fall of 2004.

[0005] It is also known that SMA wires begin to shorten at temperatures equal to or above the austenite initiation temperature As, and reach their final length when heated to a temperature equal to or above the austenite final temperature Af. Shape memory alloy wires, typically shortened in a controlled manner via heating through an electric current channel (Joule effect), are used to displace one or more elements in an actuator.

[0006] Some actuators also incorporate the use of SMA wires in conjunction with magnetic elements. In particular, U.S. Patent 8,528,597 describes the use of magnets as a biasing device for SMA wire-based actuators to reduce the force exerted by the SMA wires for actuation or locking functions. Furthermore, U.S. Patent Application 2009 / 0236931 describes the use of a pair of magnets—one of which is fixed—as an additional SMA wire biasing device.

[0007] U.S. Patent Application 2008 / 0006112 relates to a transmission system that, in a broad sense, describes an SMA line with a fixed permanent magnet to unlock a blocking member with a fixed second permanent magnet.

[0008] U.S. Patent Application 2012 / 0151913 describes a valve control module that controls the fluid portion of a valve but is isolated from it, and is also envisioned as a magnetic coupling part of a valve opening device. Summary of the Invention

[0009] The object of the present invention is to provide an actuator using SMA wires and one or more sets of permanent magnets for reciprocating motion of an element, such that coupled magnetic response elements provide means for driving a movable actuator element and means for accelerating the actuator back to a stationary position according to the actuator state. Furthermore, in a first aspect of the invention, the object is to provide an actuator subassembly comprising:

[0010] - First fixed surface and second fixed surface

[0011] -First movable element and second movable element,

[0012] - A shape memory alloy wire, which is fixed to a first fixed surface and connected to a first movable element, so as to allow the first movable element to move.

[0013] - A biasing device, which is connected to a second fixed surface and to one of a movable element that acts in the opposite manner to the driving force applied by the shape memory alloy wire.

[0014] The first movable element and the second movable element are magnetically coupled via a magnetic response element comprising one or more sets of permanent magnets and corresponding magnetic response elements (i.e., magnets with opposite magnetic properties and / or ferromagnetic materials), such that the displacement of the second movable element is driven by the displacement of the first movable element when actuated by the SMA line, and the magnetic coupling also provides for the return of the two movable elements to their rest positions via a biasing device when the SMA line is de-actuated, wherein a second fixed surface is interposed between the first movable element and the second movable element, thereby separating the first movable element and the second movable element, preferably in a fluid-tight manner.

[0015] The present invention also provides a more balanced actuator sub-assembly structure, wherein the second movable element (the element that performs the action of the actuator) is not subjected to asymmetrical forces as in the case of the first movable element, because the shape memory alloy wires attached to the second movable element are located in a specific plane, thereby resulting in a smoother functioning of the actuator sub-assembly.

[0016] Furthermore, in a preferred embodiment of the actuator subassembly according to the invention, the SMA line and the biasing device are physically separated by a first movable element located on opposite sides of them. This physical separation provides greater design flexibility and ease of assembly for the actuator subassembly, especially considering that some actuator subassemblies can be adopted in microsystems, since the SMA line can be conveniently used not only in a linear configuration but also in so-called U-shaped or V-shaped configurations that allow for greater strength and / or travel of the SMA line. An example of an actuator limited to a linear configuration is shown in Japanese Patent Application 2009 / 075170, in which the linear SMA line and the biasing device are both concentrically connected between a first fixed surface and a first movable element, i.e., they are located on the same side of the first movable element, thereby making it substantially impossible to use any other configuration of the SMA line.

[0017] It is important to emphasize that this configuration allows for a greater degree of miniaturization because, in this case, the SMA actuator is fully integrated into the valve fluid module. This differs from the description in the aforementioned U.S. patent application 2012 / 0151913, in which the control module is replaced with the fluid portion of the valve. The most relevant difference between US2012 / 0151913 and this invention is the lack of separation between the shape memory alloy wire and the biasing device, and the fact that the magnetic response element is not directly mounted on the movable element but requires an intermediate element, thus increasing the structural burden.

[0018] Conversely, another advantage of the configuration of this invention is particularly relevant to fluid valve applications, because in this case, the shape memory alloy wire will always be exposed to air, regardless of the specific properties of the fluid (liquid, gas, mixture), thereby ensuring better thermal management and control of the shape memory alloy wire and its actuation. This will also allow for full proportionality of the valve, rather than being limited to a finite number of operating positions as described in US2012 / 0151913, a limitation associated with the use of bistable / tristable biasing devices, which differ from the preferred implementation of proportional biasing—such as springs, flexible elements, etc.—contemplated by this invention.

[0019] It should be emphasized that the first and second fixed surfaces will be interpreted in the context of the actuator sub-assembly. More specifically, the actuator sub-assembly of the present invention can be mounted on a movable device (e.g., an automobile), and thus they can be understood accordingly as fixed surfaces. Attached Figure Description

[0020] The invention will be further described with reference to the following figures, in which:

[0021] Figure 1A and Figure 1B A schematic cross-sectional view of a first embodiment of the actuator subassembly according to the present invention, in an unactuated state and an actuated state, is shown.

[0022] Figure 2A and Figure 2B A schematic cross-sectional view of a second embodiment of the actuator subassembly according to the present invention, in an unactuated state and an actuated state, is shown.

[0023] Figure 3A and Figure 3B A schematic cross-sectional view of a third embodiment of the actuator subassembly according to the present invention is shown in an unactuated state and an actuated state, respectively.

[0024] Figure 4A and Figure 4B A schematic cross-sectional view of a fourth embodiment of the actuator subassembly according to the present invention, in an unactuated state and an actuated state, is shown.

[0025] Figure 5A and Figure 5B A schematic cross-sectional view of a fifth embodiment of the actuator subassembly according to the present invention, in an unactuated state and an actuated state, is shown, and

[0026] Figure 6 A schematic cross-sectional view of a valve including an actuator subassembly according to the present invention is shown. Detailed Implementation

[0027] For clarity, the dimensions and proportions of the various components shown in the accompanying drawings may have been altered, specifically but not exclusively relating to the diameter of the shape memory alloy wire; furthermore, some elements that are not essential for understanding the invention—such as shape memory alloy wire crimping portions, electrical contacts, etc.—are not shown in the schematic diagrams.

[0028] Figure 1A and Figure 1B An exemplary cross-sectional view of the actuator sub-assembly 10 according to a first embodiment of the invention is shown in a rest position (SMA line is in an unactuated state) and an operating position (SMA line is in an actuated state).

[0029] The actuator subassembly 10 includes a first top fixed surface 11, a second bottom fixed surface 12, a first movable element 13 located outside the element 12, and a second movable element 14 located inside the element 12. These two movable elements 13 and 14 are preferably coaxial with respect to each other. Displacement of the first movable element 13 is caused by a shape memory alloy wire 15 in a so-called V-shaped configuration, wherein the end of the shape memory alloy wire 15 is fixed to the first fixed surface 11 and the central portion of the shape memory alloy wire 15 is fixed / connected to the first movable element 13.

[0030] When the shape memory alloy wire 15 is actuated, the first movable element 13 rises and the second movable element 14 is also driven upward by the attraction of the first magnet 17 mounted on the first movable element 13 and the second magnet 17' mounted on the second movable element 14.

[0031] When the SMA line 15 is released from actuation, the second movable element 14 pulls the first movable element 13 toward its rest position by means of the magnetic attraction of the magnets 17, 17' and by means of the biasing element—in this case, the spring 16 connected between the second fixed surface 12 and the second movable element 14.

[0032] exist Figure 1A and Figure 1B In this design, terminal element 18 is represented as a free tip attached to the second movable element 14 and its function is characterized by its relationship to the supports 19, 19' of the second fixed surface 12. More specifically, the invention is not limited to a particular shape, material, or use of terminal 18. For example, terminal 18 may be an electronic terminal for contacting elements 19, 19', or terminal 18 may be a plunger (in which case 19 and 19' are the walls of the opening) or a door lock or magnetic clutch for closing an opening in a fluid circuit.

[0033] Figure 1A and Figure 1BThe schematic cross-sectional view shows a sub-assembly using two magnets 17 and 17' with opposite polarities, the ring-shaped magnets being attached to a first movable element 13 and a second movable element 14, respectively.

[0034] Figure 2A and Figure 2B A schematic cross-sectional view of the actuator sub-assembly 20 according to a second embodiment of the invention is shown in a rest position (SMA line is in an unactuated state) and an operating position (SMA line is in an actuated state).

[0035] Compared to Figure 1A and Figure 1B The most important structural difference in the first embodiment shown is the positioning of the biasing element / reset spring 26, which is now connected between the first movable element 23 and the second fixed surface 22, and thus applies a pulling action instead of a pushing action like that of spring 16.

[0036] Figures 1A to 1B The reset element 16 and Figures 2A to 2B The different positioning of the reset element 26 highlights the two main configurations of the actuator subassembly according to the invention.

[0037] Other differences in actuator subassembly 20 are merely variations and therefore can also be applied to the configuration of actuator subassembly 10, as follows:

[0038] • A shape memory alloy wire 25 in a straight / linear configuration, wherein one end of the shape memory alloy wire 25 is fixed to a first fixed surface 21 and the other end is fixed to a first movable element 23;

[0039] • A second movable element 24, now made of magnetic material 27', is used for magnetic coupling with the magnetic element 27 mounted on the first movable element 23.

[0040] Similar to Figure 1A The terminal element 28 at the tip of the second movable element 24 determines the range and function of the actuator sub-assembly by its relationship with the sub-assembly elements 29, 29', which serve as supports for the second fixed surface 22.

[0041] Figure 3A and Figure 3B A schematic cross-sectional view of a third embodiment of the actuator subassembly 30, in its rest position and in its operating position, is shown. Figures 1A to 1BAs in the first embodiment shown, a biasing spring 36 is also present between the second movable element 34 and the second fixed surface 32. In this case, the terminal 38 is not an element attached to the second movable element 34 but rather a portion of the second movable element 34 most suitable for sealing the fluid valve port, particularly the tip portion, whereby the supports 39, 39' of the second fixed surface 32 will represent a portion of the valve wall or generally represent the valve insulating element.

[0042] In the actuator subassembly 30, a V-shaped SMA line 35 connects a first fixed surface 31 to a first movable element 33. The first movable element 33 carries a magnetic element 37, preferably a cylindrical member with a significant longitudinal extension, while a plurality of smaller annular magnetic elements 37' are spaced apart along a second movable element 34. When the SMA line 35 is actuated, the first movable element 33 rises and drives the second movable element 34 upward through the magnetic coupling between the magnetic element 37 and the plurality of magnetic elements 37'. When the SMA line 35 is cooled, the second movable element 34 pulls the first movable element 33 downward through the magnetic coupling due to the push of a bias spring 36 connected between the second fixed surface 32 and the second movable element 34.

[0043] Figure 4A and Figure 4B A schematic cross-sectional view of a fourth embodiment of the actuator subassembly 40 is shown, in its rest position and in its operating position, respectively. This structure is related to... Figures 1A to 1B The first embodiment shown is almost identical, and the structure includes a first top fixed surface 41, a second bottom fixed surface 42, a first movable element 43, a second movable element 44, a V-shaped SMA wire 45, a bias spring 46 connecting the second movable element 44 and the second fixed surface 42, magnetic elements 47 and 47' respectively mounted on the first movable element 43 and the second movable element 44, and a terminal 48 located at the tip of the second movable element 44 for contacting the support members 49 and 49' of the second fixed surface 42.

[0044] The only difference provided by this fact is that the magnetic element 47' mounted on the second movable element 44 also contacts the second fixed surface 42, and therefore the magnetic element 47' has a circular cross-section to minimize friction during actuation of the SMA line 45 fixed to the first movable element 43 when pulled upward by the presence of the magnetic element 47, and during de-actuation of the SMA line 45 when pushed downward by the presence of the bias spring 46. For this purpose, the magnetic element 47' is mounted such that it can rotate during relative movement between the second fixed surface 42 and the second movable element 44. For example, the magnetic element 47' is arranged between an upper crossbar and a lower crossbar 47" which are integral with the second movable element 44 and sized to avoid contact with the second fixed surface 42 while preventing the rotating magnetic element 47' from falling off.

[0045] exist Figures 1A to 4B In all embodiments shown, the actuator subassembly illustrates linear movement of the movable element; however, the same concept can be advantageously applied to rotary actuators, such as... Figure 5A and Figure 5B as exemplified in Figure 5A and Figure 5B A schematic cross-sectional view of a fifth embodiment of the actuator sub-assembly 50 according to the present invention, in an unactuated state and an actuated state, is shown.

[0046] More specifically, the actuator subassembly 50 includes a concentric first circular movable element 53 and a second circular movable element 54, the first circular movable element 53 having a magnetically responsive element 57 mounted thereon, and the second circular movable element 54 having a magnetically responsive element 57' mounted thereon. A shape memory alloy wire 55 is connected in a generally tangential manner between a point on the outer periphery of the first fixed surface 51 and the first movable element 53, while an elastic element 56, with the opposite pulling effect to the SMA wire 55, is also connected in a generally opposite position in a tangential manner between another point on the outer periphery of the first fixed surface 51 and the first movable element 53.

[0047] A circular second fixed surface 52 is concentrically arranged between the two movable elements 53 and 54 and is supported by a radially extending support 59, while the contact element (terminal) 58 is mounted flush with the outer periphery of the second movable element 54. When the SMA line 55 is actuated, the first movable element 53 rotates (in... Figure 5A , 5B (In the illustrated example, the direction is counterclockwise), and then the second movable element 54 is rotated by the coupled magnetic response elements 57, 57', thereby causing the terminal 58 to move along the support 59 and align / contact with the support 59.

[0048] All the embodiments described above demonstrate the advantage of the present invention, namely that the coupled magnetic response element achieves two functions:

[0049] • Drives the actuator element when the SMA line is actuated (heated by a current source).

[0050] • Once the SMA line is deactivated (no current source), the acceleration actuator returns to the stationary position.

[0051] According to the above description, there are two main configurations for the actuator sub-assembly according to the invention. In the first main configuration, the bias spring acts on the first movable element, and in the second main configuration, the bias spring acts on the second movable element.

[0052] These two main implementation methods can be implemented with various modifications, some of which have been shown with reference to the accompanying drawings, in particular:

[0053] • SMA wire configuration: In the most useful configuration, a single SMA wire, preferably in a straight form, is used, wherein one end of the single SMA wire is fixed to a first fixed surface and the other end is fixed to a first movable element. Alternatively, an SMA wire in a so-called V / U shape configuration is used, wherein the SMA wire has two ends both fixed to the first fixed surface and a middle portion fixed / connected to the first movable element.

[0054] • Magnetic response element: At least one group of permanent magnets shall be present on the first movable element or the second movable element, and the magnetic response element on the other movable element may be one or more groups of magnets of opposite polarity or one or more elements comprising or composed of ferromagnetic material.

[0055] The magnetically responsive element can be fixedly / connected to the first movable element and the second movable element; however, alternatively, the first movable element and / or the second movable element can comprise or be made of a magnetically responsive element / material.

[0056] • The height of the magnetic response elements can be the same, or one of the magnetic response elements can have the same height, including multiple sets of corresponding magnetic elements on another movable element.

[0057] The size and shape of the magnetic response element can vary; in this respect, a circular cross-section is preferred when the magnetic response element is in contact with the second fixed surface.

[0058] The first and second fixed surfaces can correspond to different actuator elements, or they can be part of a single element—such as an actuator frame of appropriate shape.

[0059] • The actuator sub-assembly can have linear motion or rotational motion.

[0060] All of the above variations are not limiting aspects of the invention, but merely preferred solutions that may be used in combination in the two main embodiments of the actuator subassembly.

[0061] Preferably, the magnetically responsive element comprises a set of permanent magnets that provide a magnetic drag force capable of compressing the bias spring, thereby avoiding any movement delay between the displacement of the first movable element (the external element in the described embodiment) and the displacement of the second movable element. The magnetic drag force is a force perpendicular to the magnetic attraction and is a direct result of the shape memory alloy wire pulling on the first movable element. The magnetic drag force must be between 1 and 10 times the bias spring force, preferably between 1.5 and 5 times the bias spring force, and can be readily obtained by those skilled in the art from permanent magnet datasheets.

[0062] Examples of suitable shape memory alloys used in the actuator subassemblies according to the invention are Ni-Ti based alloys, such as nickel-titanium alloys, with or without additional elements selected from Hf, Nb, Pt, and Cu. Suitable diameters for SMA wire actuator elements range from 25 to 500 μm.

[0063] A second aspect of the invention is a fluid valve that includes an actuator subassembly as described above.

[0064] In certain embodiments, the second stationary surface is fluid-sealed, preventing the shape memory alloy wire from contacting any fluid. This allows the use of fluids whose properties and characteristics could damage the shape memory alloy wire, such as water, oil, or refrigerant fluids (e.g., so-called R410a). As already outlined, contact with these fluids can affect SMA wire actuation, which is typically achieved through Joule heating.

[0065] Figure 6The diagram shows a schematic cross-sectional view of a fluid valve 600 comprising an actuator subassembly according to the invention. The valve 600 has a fluid inlet 601 and a fluid outlet 602, which are selectively connected or isolated by means of a plunger corresponding to a second movable element 64 and having a suitable terminal portion 68 for a fluid-tight connection, possibly by means of an annular washer 68', which is optional where the size of the outlet 602 preferably matches the size of the terminal portion 68; alternatively, the plunger may be an element performing a flow control function, such as a calibration orifice. The second movable element 64 and a first movable element 63 are fluid-tightly separated from each other by a second fixed surface 62, which is supported by and connected to the valve body 603. A bias spring 66 connects the second movable element 64 to the second fixed surface 62.

[0066] Valve 600 is shown in what is called a normally closed configuration. Figure 6 In this case, when the SMA line 65 is in an unactivated state, the inlet 601 and the outlet 602 are isolated from each other. When the V-shaped SMA line 65 connecting the first fixed surface 61 and the first movable element 63 is activated, the first movable element 63 rises, and through the action of the magnetic response elements 67 (present on the first movable element 63) and 67' (present on the second movable element 64), the second movable element / plunger 64 is dragged upward, thereby fluidly communicating the inlet 601 and the outlet 602.

[0067] When the shape memory alloy wire 65 is released from actuation, the bias spring 66 pushes the second movable element / plunger 64 downward to close the valve 600, and in this movement it is also dragged along the first movable element 63 toward the rest position of the first movable element 63 by the magnetic coupling of the elements 67, 67'.

Claims

1. An actuator sub-assembly (10; 20; 30; 40; 50) comprising: - a first fixed surface (11; 21; 31; 41; 51; 61) and a second fixed surface (12; 22; 32; 42; 52; 62), - a first movable element (13; 23; 33; 43; 53; 63) and a second movable element (14; 24; 34; 44; 54; 64), - a shape memory alloy wire (15; 25; 35; 45; 55; 65) fixed to the first fixed surface (11; 21; 31; 41; 51; 61) and connected to the first movable element (13; 23; 33; 43; 53; 63) to move the first movable element (13; 23; 33; 43; 53; 63) from a rest position to an operating position, - a biasing device (16; 26; 36; 46; 56; 66) connected to one of the fixed surfaces and to one of the movable elements so as to act in opposition to the driving force exerted by the shape memory alloy wire (15; 25; 35; 45; 55; 65). said first movable element (13; 23; 33; 43; 53; 63) and said second movable element (14; 24; 34; 44; 54; 64) are connected via magnetic coupling through magnetic responsive elements (17, 17'; 27, 27'; 37, 37'; 47, 47'; 57, 57'; 67, 67') comprising one or more sets of permanent magnets located on one of said movable elements and one or more corresponding magnetic responsive elements located on the other of said movable elements, such that the displacement of said first movable element (13; 23; 33; 43; 53; 63) upon actuation by heating of said shape memory alloy wire (15; 25; 35; 45; 55; 65) by a current source also causes the displacement of said second movable element (14; 24; 34; 44; 54; 64) from a rest position to an operating position, said magnetic coupling also providing the return of both movable elements towards their rest position by said biasing means (16; 26; 36; 46; 56; 66) upon de-actuation of said shape memory alloy wire (15; 25; 35; 45; 55; 65), characterized in that said second fixed surface (12; 22; 32; 42; 52; 62) is interposed between said first movable element (13; 23; 33; 43; 53; 63) and said second movable element (14; 24; 34; 44; 54; 64), thereby separating said first movable element (13; 23; 33; 43; 53; 63) and said second movable element (14; 24; 34; 44; 54; 64), wherein both ends of said shape memory alloy wire (15; 35; 45) are fixed to said first fixed surface (11; 31; 41) and the intermediate portion of said shape memory alloy wire (15; 35; 45) is connected to said first movable element (13; 33; 43) in a V-shaped configuration or a U-shaped configuration.

2. The actuator subassembly (10; 20; 30; 40; 50) according to claim 1, wherein said one or more sets of permanent magnets have between 1 and 10 times the force of said biasing means (16; 26; 36; 46; 56; 66).

3. The actuator subassembly (10; 20; 30; 40; 50) according to claim 1 or 2, wherein said magnetic responsive elements (17, 17'; 27, 27'; 37, 37'; 47, 47'; 57, 57'; 67, 67') are one or more permanent magnets and one or more ferromagnetic elements, respectively.

4. The actuator subassembly (10; 20; 30; 40; 50) according to claim 1 or 2, wherein said magnetic responsive elements (17, 17'; 27, 27'; 37, 37'; 47, 47'; 57, 57'; 67, 67') are one or more permanent magnets having a first polarity and one or more permanent magnets having an opposite polarity, respectively.

5. The actuator subassembly (10; 20; 30; 40; 50) according to claim 1 or 2, wherein The magnetic responsive elements (17, 17'; 27, 27'; 37, 37'; 47, 47'; 57, 57'; 67, 67') are fixed to or constitute at least a portion of the first movable element (13; 23; 33; 43; 53; 63) and the second movable element (14; 24; 34; 44; 54; 64).

6. The actuator subassembly (20) of claim 5, wherein, The second movable element (24) is essentially made of a magnetic material.

7. The actuator subassembly (10; 20; 40) according to claim 1 or 2, wherein The one or more sets of permanent magnets and the magnetic responsive elements (17, 17'; 27, 27'; 47, 47') have substantially the same height.

8. The actuator subassembly (30) of claim 1 or 2, wherein, The height of one of the magnetic responsive elements (37) located on one of the movable elements comprises more than one set of permanent magnets or more than one magnetic responsive element (37') located on the other of the movable elements.

9. The actuator subassembly (10; 20; 30; 40; 50) according to claim 1 or 2, wherein The first movable element (13; 23; 33; 43; 53; 63) and the second movable element (14; 24; 34; 44; 54; 64) are coaxial or concentric with respect to each other.

10. The actuator subassembly (40) of claim 1 or 2, wherein, The second stationary surface (42) is physically contacted by the magnetic responsive element (47') mounted on the second movable element (44).

11. The actuator subassembly (40) of claim 10, wherein, The magnetic responsive element (47') has a circular cross-section and is mounted such that it can rotate during relative movement between the second stationary surface (42) and the second movable element (44).

12. The actuator subassembly (10; 20; 30; 40; 50) according to claim 1 or 2, wherein The biasing means (16; 26; 36; 46; 56; 66) provide a proportional return force for the shape memory alloy wire (15; 25; 35; 45; 55; 65).

13. The actuator subassembly (10; 20; 30; 40; 50) according to claim 1 or 2, wherein The shape memory alloy wire (15; 25; 35; 45; 55; 65) and the biasing means (16; 26; 36; 46; 56; 66) are physically separated by the first movable element (13; 23; 33; 43; 53; 63).

14. The actuator subassembly (10; 20; 30; 40; 50) according to claim 1, wherein, The second stationary surface (12; 22; 32; 42; 52; 62) is interposed between the first movable element (13; 23; 33; 43; 53; 63) and the second movable element (14; 24; 34; 44; 54; 64), thereby separating the first movable element (13; 23; 33; 43; 53; 63) and the second movable element (14; 24; 34; 44; 54; 64) in a fluid-tight manner.

15. A fluid valve (600) comprising the actuator sub-assembly (10; 20; 30; 40; 50) according to any one of claims 1 to 14.

16. The fluid valve (600) of claim 15, wherein, The second stationary surface (62) provides a fluid-tight connection between the second movable element (64) and the first movable element (63).

17. The fluid valve (600) according to claim 15 or 16, wherein The biasing means (66) provide a proportional return force for the shape memory alloy wire (65).

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