Abstract:
A shape memory alloy (SMA) actuator for engaging and actuating a device. The actuator includes an engagement mechanism, a bias element, and a SMA object(s). The SMA actuator may automatically and passively transfer to a backup or redundant feature that resets or extends the actuator&#39;s operational life. In one embodiment, the SMA actuator includes an additional SMA object(s) that replaces the primary SMA object(s) in the event the primary SMA object(s) breaks. The SMA actuator may also be configured to apply a dynamic stress to the SMA object during transition of the object to modify the transition temperatures of the object. The SMA actuator may be part of a fluid distribution system, such as a heating, ventilation, and air conditioning (HVAC) system and used to control the flow of fluid, such as air, from the distribution system.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to, and any benefit of, U.S. Provisional Patent Application Ser. No. 60/861,814, filed on Nov. 30, 2006, entitled SHAPE MEMORY ALLOY ACTUATOR, the entire disclosure of which is fully incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Shape memory alloys (SMAs) are metallic alloys that may recover apparent permanent strains when they are heated above a certain temperature. SMAs have two stable states or phases; a hot or austenite state and a cold or martensite state. The temperatures at which the SMA changes states (i.e. its crystallographic structure) are a characteristic of the particular alloy. Selecting the material composition of the alloy and anneal temperatures of the alloy may be used to control the alloy&#39;s transition temperatures. 
         [0003]    In the austenite state, the alloy is hard and rigid, while in the martensite state, the alloy is softer and flexible. In the martensite state, the SMA may be stretched or deformed by an external force. Upon heating, the SMA will return to its austenite state and contract or recover any reasonable stretch that was imposed on it. Thus, the SMA recovers with more force that was required to stretch it out. This exerted force upon contraction may be used to perform any number of tasks such as, but not limited to, turning a device on or off, opening or closing an object, or actuating a device or object. 
         [0004]    HVAC systems provide air or another fluid to compartments, such as rooms for example. A diffuser may be provided at the system outlet to distribute, in a particular way, the air or other fluid entering the room. For example, the diffuser may have one or more blades to direct the flow of the air. 
         [0005]    Due to the buoyancy effect of air (i.e. cold air will naturally sink and hot air will naturally rise), heating air and cooling air are preferably provided to a room in different patterns. When both heating and cooling air are provided to the room through a single diffuser, the ability to adjust the diffuser to provide different flow patterns is desirable. Some diffusers may be manually adjusted while other diffusers may sense supply air temperature and adjust the diffuser through the use of a powered control system, bimetallic strips, or wax motors. 
       SUMMARY  
       [0006]    The present application is directed to a shape memory alloy (SMA) actuator. The actuator may have an engagement mechanism for engaging and actuating a device, a bias element associated with the engagement mechanism, and an SMA object(s) associated with the engagement mechanism. The SMA object(s) may expand or contract based on the object&#39;s temperature. When the temperature increases past a first predetermined value, the SMA object(s) may contract and move the engagement mechanism to a first position. When the temperature decreases past a second predetermined value, the SMA object may expand and the bias element may move the engagement mechanism to a second position. 
         [0007]    The present application also discloses an exemplary SMA actuator that may automatically and passively transfer to a backup or redundant feature that resets or extends the actuator&#39;s operational life. In one exemplary embodiment, an SMA actuator may include an additional or redundant SMA object(s) that replaces the primary SMA object(s) in the event the primary SMA object(s) fails. The actuator may have the additional or redundant SMA object(s) attached to a movable part in such a way that if the primary or active object(s) fails, the redundant object(s) moves into an active position. In one embodiment, the movable part is a rotatable cam mechanism and the SMA object(s) is an SMA wire(s). 
         [0008]    In another exemplary embodiment, the actuator uses multiple SMA objects that each has an individual stress load to allow for consistency in the transitions temperatures of actuator. Thus, in the event of a single SMA object failure, the secondary SMA object will have the proper stress load and continue to operate at the intended transition temperatures. 
         [0009]    In another exemplary embodiment, the SMA actuator may be configured to be part of a fluid distribution system, such as a heating, ventilation, and air conditioning (HVAC) system, and, more particularly, may be used to control the flow of fluid, such as air, from the distribution system. The SMA actuator may cooperate with at least one blade of the diffuser to change the position of the blade in response to the temperature of the fluid without requiring an external energy source. In one embodiment, an SMA object(s) in the actuator contracts in a heating mode and expands in a cooling mode. In another embodiment, the SMA object(s) may connect directly or indirectly with the at least one blade. 
         [0010]    Also disclosed is an exemplary diffuser for use in a fluid distribution system. The diffuser may include at least one blade for directing the flow of fluid from the distribution system, and an actuator as described above. Also disclosed is an exemplary fluid distribution system having one or more diffusers, such as the exemplary diffuser described above. 
         [0011]    In present application is also directed to an exemplary method for controlling the transition temperature of an SMA object by precisely controlling the stress load imposed on the SMA material. In one exemplary embodiment, the transition temperatures of an SMA actuator are controlled by selecting the stress load placed on the SMA object. In another exemplary embodiment, a dynamic stress load is applied to the SMA object during transition of the object to modify the transition temperatures of the SMA object. Thus, the dynamic stress load allows for the creation of changing temperatures of reaction. For example, in one exemplary embodiment, the stress load on an SMA object is reduced as the SMA object transitions from the martensite state to the austenite state in order to ensure complete transition to the austenite state once the transition begins. 
         [0012]    Further aspects and concepts will become apparent to those skilled in the art after considering the following description and appended claims in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    In the accompanying drawings, which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to exemplify embodiments of the invention: 
           [0014]      FIG. 1  is a front view of an exemplary embodiment of an SMA actuator; 
           [0015]      FIG. 2  is a rear view of the exemplary actuator of  FIG. 1 ; 
           [0016]      FIG. 3  is a top view of the exemplary actuator of  FIG. 1 ; 
           [0017]      FIG. 4  is a top view of the exemplary actuator of  FIG. 1  with the bracket hidden; 
           [0018]      FIG. 5  is a side view of the exemplary actuator of  FIG. 1 ; 
           [0019]      FIG. 6  is an isometric rear view of the exemplary actuator of  FIG. 1 ; 
           [0020]      FIG. 7  is an isometric rear view of the exemplary actuator of  FIG. 1  enlarged in the area of the cam mechanism with the bracket hidden; 
           [0021]      FIG. 8  is a temperature versus strain graph of an SMA wire of the exemplary actuator of  FIG. 1  at a first stress load; 
           [0022]      FIG. 9  are temperature versus strain graphs of the SMA wire of  FIG. 8  at the first stress load and a second stress load; 
           [0023]      FIG. 10  is a temperature versus strain graph of the SMA wire of  FIG. 8  illustrating an impact of dynamic stress loading; 
           [0024]      FIG. 11  is a top view of an exemplary embodiment of the cam mechanism of the exemplary actuator of  FIG. 1  in a first position; 
           [0025]      FIG. 12  is a top view of the exemplary embodiment of the cam mechanism of the exemplary actuator of  FIG. 1  in a second position; 
           [0026]      FIG. 13  is a top view of the exemplary embodiment of the cam mechanism of the exemplary actuator of  FIG. 1  in a third position 
           [0027]      FIG. 14  is a top view of the exemplary embodiment of the cam mechanism of the exemplary actuator of  FIG. 1  in a fourth position; 
           [0028]      FIG. 15  is a side view of an exemplary embodiment of a fluid distribution system utilizing the exemplary actuator of  FIG. 1 , illustrated in a first position; and 
           [0029]      FIG. 16  is a side view of the exemplary fluid distribution of  FIG. 15 , illustrated in a second position. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The present application discloses a shape memory alloy (SMA) actuator. While the exemplary embodiments illustrated and described herein are presented in the context of an air diffuser actuator having two pairs of SMA wires, each pair attached to a respective spring via a rotatable cam mechanism that may switch the force of the spring from one of the wires to the other, those skilled in the art will readily appreciate that the present invention may be used and configured in other ways. For example, the SMA actuator is not limited to use with an air diffuser or other fluid distribution device. The SMA actuator may be operatively associated with a wide variety of actuatable devices in a wide variety of applications, such as, but not limited to, aerospace, military, medical, safety, and robotics applications. 
         [0031]    In the context of a diffuser, the actuator may be used for the dispersion and distribution of any fluid, and not just air, into any compartment, or an open area. The fluid may be, for example, a gas of combination of gases other than air. Furthermore, the actuator may utilize one or more SMA objects other than wires or may include only a single pair of SMA wires or more than two pairs of wires. Still further, the movable part that switches the force of the spring from one of the pair of wires to the other need not be a rotatable cam mechanism. Any movable part that may automatically switch the spring&#39;s load may be used. In addition, a biasing element other than a spring may be used. Any device capable of applying a stress load to an SMA object may be suitable. 
         [0032]    While various aspects and concepts of the invention are described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects and concepts may be realized in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub-combinations are intended to be within the scope of the present invention. Still further, while various alternative embodiments as to the various aspects and features of the invention, such as alternative materials, structures, configurations, methods, devices, and so on may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or identified herein as conventional or standard or later developed. Those skilled in the art may readily adopt one or more of the aspects, concepts or features of the invention into additional embodiments within the scope of the present invention even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the invention may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present invention however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated. 
         [0033]    For the purposes of this application, the terms attach (attached), connect (connected), and link (linked) are not limited to direct attachment, connection, or linking but also include indirect attachment, connection, or linking with intermediate parts, components, or assemblies being located between the two parts being attached, connected, or linked to one another. 
         [0034]      FIGS. 1-6  illustrate an exemplary embodiment of an SMA actuator  10 . The SMA actuator  10  may include a bracket  12  having a first end  14  and a second end  16 . The bracket  12  may include a top wall  18  that is generally parallel to a bottom wall  20  and connected to the bottom wall by a front wall  22 . The bracket  12  may define a channel  24  in which a first SMA arrangement  26  and a second SMA arrangement  28  may be disposed. The SMA actuator  10 , however, may include only a single SMA arrangement or may include more than two SMA arrangements. 
         [0035]    In the depicted embodiment, the first SMA arrangement  26  is substantially similar to the second SMA arrangement  28 ; thus, only the first SMA arrangement will be discussed in detail. The first SMA arrangement  26  may include a first or primary SMA wire  30  and a second or secondary SMA wire  32 . The SMA wires  30 ,  32  are at least partially composed of a shape memory alloy (SMA). The wires must have sufficient SMA to react to temperature changes to produce the actuator changes described herein. References herein to an SMA wire include a wire partially composed of an SMA and a wire that is completely composed of SMA. 
         [0036]    In the exemplary embodiment shown, the first SMA wire  30  has a first end  34  and a second end  36  and the second SMA wire  32  has a first end  38  and a second end  40 . The first end  34  of the first SMA wire  30  and the first end  38  of the second SMA wire  32  may be fixably attached to the first end  14  of the bracket  12 . The second end  36  of the first SMA wire  30  and the second end  40  of the second SMA wire  32  may be attached to a movable or rotatable part  42 , such as a cam mechanism for example. 
         [0037]    The first SMA arrangement  26  may also include one or more bias elements  44 , such as for example one or more springs, as illustrated in  FIGS. 1-7 . The spring  44  may have a first end  46  attached to the cam mechanism  42  and a second end  48  attached to the second end  16  of the bracket  12 . The bracket  12  may have multiple locations or spring pin adjustments  49  to which the second end  48  of the spring  44  may attach to the bracket. The multiple spring pin adjustments  49  allow for adjustments to the size of the spring  44  or the amount of bias force a given spring imposes within the arrangement. The spring  44  and the first and the second SMA wires  30 ,  32  may be generally arranged along the same axis, though that is not required. 
         [0038]    The SMA actuator  10  may also include a lever  50 . The lever  50  may be pivotally attached to the bracket  12  by a pivot pin  52  such that the lever may pivot about the pin. The lever  50  may include a first end  54  that is attached to the cam mechanism  42  and a second end  56  that may include an engagement mechanism  58  that engages a portion of an actuated device, such as for example an air diffuser  60  (as described in detail in relation to  FIGS. 15 and 16 ). 
         [0039]    The first SMA wire  30  and the second SMA wire  32  may have two stable states or phases, a hot or austenite state and a cold or martensite state. In the austenite state, the SMA wires  30 ,  32  are hard and rigid and in the martensite state, the SMA wires are softer and flexible. In the martensite state, the SMA wires  30 ,  32  may be stretched or deformed by an external force. Upon heating, the SMA wires  30 ,  32  may change states to the austenite state. Upon changing to the austenite state, the SMA wires  30 ,  32  may contract or recover any reasonable stretch that was imposed on it. 
         [0040]      FIG. 8  illustrates a temperature vs. strain graph of an exemplary implementation of the first SMA wire  30  with a first constant stress load imposed upon the wire. M S  denotes the temperature at which the first SMA wire  30  generally starts to change from austenite to martensite upon cooling and M F  denotes the temperature at which the transition is generally finished. Accordingly, A S  and A F  denote the temperatures at which the reverse transformation from martensite to austenite generally starts and generally finishes, respectively. Curve  1  depicts the transition of the first SMA wire  30  from the cold or martensite state to the hot or austenite state. As shown, during the state transition, the first SMA wire  30  contracts or recovers the strain between strain ε M  and ε A  over a generally small temperature range. Thus, the state transition may, in general, occur rapidly as the temperature of the SMA rises. Curve  2  depicts the transition of the first SMA wire  30  from the austenite state to the martensite state. Similar to Curve  1 , the transition may occurs rapidly, over a generally small temperature range. As illustrated, the start temperature M S  and finish temperature M F  of the first SMA wire  30  when transitioning to the martensite state differs from the start temperature A S  and finish temperature A F  of the first SMA wire when transitioning to the austenite state. 
         [0041]    The first and second SMA wires  30 ,  32  have an internal hysteresis that is a material property of the SMA used. For example, in the context of a HVAC system, the normal operating supply air temperatures are about 55° F. in cooling and about 85° F. in heating. When an SMA is at a temperature less than a first selected temperature, for example, 60° F., it is at its fully expanded or martensite state. As the air temperature increases, there is slight contraction of the material, but at a second selected temperature, for example, 80° F., there is a drastic contraction of the material and at any temperature above 80° F. the material will be in a fully contracted or austenite state. The SMA wire may change its geometry within about one to two seconds, however, the SMA wire may change faster or slower depending on the rate of temperature change. The actual time for the SMA wire to undergo change depends on the material selected for the SMA wire (see below). As the same wire cools, it does not re-expand at 80° F. It only fully expands at 60° F. 
         [0042]    Thus, the SMA wire essentially undergoes a prompt or non-gradual change at selected temperatures. This enables the SMA actuator  10  to move the actuated device rapidly. The actual time it takes to actuate a device depends on the configuration of the actuator and the device and the direct or indirect connection between the SMA wire and the device. 
         [0043]      FIG. 9  illustrates two temperature vs. strain graphs for the exemplary implementation of the first SMA wire  30 , each at a different constant stress level imposed upon the first SMA wire. Curves  1  and  2  are identical to curves  1  and  2  of  FIG. 8 , which is at the first constant stress level. Curves  3  and  4  illustrate the transitions of the first SMA wire  30  at a second constant stress level that is higher that than first constant stress level. During heating, the amount of force or load exerted on the first SMA wire  30  can shift/raise/lower the transition temperature at which it returns to austenite. During cooling, the amount of force or load exerted on the first SMA wire  30  can shift/raise/lower the transition temperatures at which it returns to martensite. Controlling the load on the SMA will control the transition temperatures and allow the SMA&#39;s temperature versus strain characteristics to be customized. 
         [0044]    Raising the constant stress load on the first SMA wire  30  increases the start and finish temperatures of both transitions. Thus, the start temperatures M S2  and A S2  at the higher constant stress are greater that the start temperatures M S1 , A S1 , at the lower constant stress. Similarly, the finish temperatures M F2  and A F1  at the higher constant stress are greater that the finish temperatures M F1 , A F1  at the lower constant stress. Therefore, changing the amount of stress on the first SMA wire impacts the temperatures at which the wire transitions between states. As shown in  FIG. 9 , the martensite transition temperatures are raised slightly more that the austenite transition temperatures as a result of the same load increase. 
         [0045]      FIG. 10  illustrates the temperature vs. strain graph of  FIG. 8  at the first constant stress level (i.e. curve  1  and curve  2 ) as well as curves  5  and  6 , which illustrate an example of how the transition temperatures and curve shape may be modified when the stress level on the wire is dynamically changed (raised or lowered) during the transition. In curve  5 , the stress load on the first SMA wire  30  is increased during the wire&#39;s transition from martensite to austenite. As a result, curve  5  takes on a more linear transition than with the wire had with a constant stress load (curve  1 ). Conversely, if the stress load on the first SMA wire  30  is reduced during the transition from martensite to austenite, the curve (not shown) would be flat or flatter (rapid strain change over a small temperature range) than curve  1 . Similarly, in curve  6 , the stress load is reduced during the transition from martensite to austenite. As a result, curve  6  takes on a more linear appearance. If the stress load on the first SMA were increased during the transition from martensite to austenite, than the curve (not shown) would be flatter. 
         [0046]    Referring to  FIG. 11 , the SMA actuator  10  is depicted in a first position in which the first and second SMA wires  30 ,  32  are in the hot or austenite state. In the first position (and second position), the first SMA wire  30  and the spring  44  are generally co-axial, though that is not required. The second SMA wire  32  attaches to the cam mechanism  42  offset a distance D from the attachment point between the spring  44  and the cam mechanism  42 . The spring  44  applies a first amount of tension to the first SMA wire  30  through the cam mechanism  42 . The second SMA wire  32  is under little or no tension, however, because it has a length that is longer than the distance between where the second SMA wire  32  attaches to the first end  14  of the bracket  12  and where the second SMA wire  32  attaches to the cam mechanism  42 . In other words, there is slack in the second SMA wire  32 . Therefore, in the first position, the first SMA wire  30  is in an active position (positioned to be stressed by the spring  44 ) and the second SMA wire  32  is in an inactive position (positioned to not be subject to stress from the spring  44 ). In the first position, the lever  50  may also be considered to be in a first lever position. 
         [0047]    Referring to  FIG. 12 , the SMA actuator  10  is depicted in a second position in which first and second SMA wires  30 ,  32  are in the cold or martensite state. In the second position, the first SMA wires  30  has been stretched or deformed by an external force, such as for example the bias force of the spring  44 . Thus, as the temperature of the first SMA wire  30  decreases and reaches the martensite transition start temperature M S , the first SMA wire begins transitioning from the hot or austenite state to the cold or martensite state. In the martensite state, the stress on the first SMA wire  30  from the spring  44  stretches or deforms the wire. As the spring  44  stretches the first SMA wire  30 , the spring compresses and moves the cam mechanism  42  to the right, as viewed in the  FIGS. 11-14 . As the cam mechanism  42  moves to the right, the lever  50  pivots from the lever&#39;s first position to the lever&#39;s second position. 
         [0048]    During the transition of the first SMA wire  30 , the second SMA wire  32  may also change states from austenite to martensite. The second SMA wire  32 , however, is not subjected to the stress of the spring  44 . Thus, the second SMA wire  32  is not deformed when the first SMA wire  30  is deformed. The second SMA wire  32 , however, will move with the cam mechanism  42  due to the slack in the wire, but it is not active. 
         [0049]    From the martensite state, the SMA wires  30 ,  32  may transition back to the austenite state if they are heated above the austenite transition start temperature As. During transition to the austenite state, the first SMA wire  30  contracts. The force of the contraction overcomes the bias force imposed by the spring  44 . Thus, as the first SMA wire  30  contracts, it expands the spring  44  and moves the cam mechanism  42  to the left, as viewed in the  FIGS. 11-14 . As the cam mechanism  42  moves to the left, the mechanism pivots the lever  50  from the lever&#39;s second position to the lever&#39;s first position. 
         [0050]    During the transition of the first SMA wire  30 , the second SMA wire  32  may also change states from martensite to the austenite. The second SMA wire  32 , however, was generally not deformed by the spring  44  in the martensite state; thus, there is little or no deformation for the second SMA wire  32  to recover when transitioning to the austenite state. 
         [0051]      FIGS. 13 and 14  illustrate the SMA actuator  10  in a third and fourth position, respectively, which results from a failure or breaking of the first SMA wire  30 . SMA wires typically have a working temperature and stress range within which they may operate for long periods of time. Outside of the working range, however, an SMA wire can fatigue or break. 
         [0052]    If the first SMA wire  30  breaks, the cam mechanism  42  may automatically rotate to a position in which the spring  44  imposes a stress onto the second SMA wire  32 . Because the spring  44  attaches to the cam mechanism  42  offset the distance D ( FIG. 11 ) from the attachment point between the second SMA wire  32  and the cam mechanism  42 , the bias force of the spring  44  will rotate the cam mechanism  42  clockwise, as viewed in  FIGS. 11-14  when if first SMA wire  30  breaks. Thus, the second SMA wire  32  is placed into an active position and the first SMA wire  30  is in an inactive position. 
         [0053]    Rotation of the cam mechanism  42  to the position depicted in  FIGS. 13 and 14 , brings the second SMA wire  32  into a position where the spring  44  is exerting a bias force onto the second wire. Thus, the second SMA wire  32  is no longer slack in the third and fourth positions. As the cam mechanism  42  rotates, the force dynamic from the spring  44  may change. For example, the spring  44  is compressed more in the third and fourth positions than it was in the first and second positions. As previously discussed, the amount of stress on the first SMA wire  30  may impact the temperatures at which the first SMA wire transitions. Likewise, the amount of stress on the second SMA wire  32  may impact the temperatures at which the second SMA wire transitions. Since the spring  44  is more compressed in the third and fourth positions as compared to the first and second positions, respectively, the amount of bias force from the spring  44  on the second SMA wire  32  in the third and fourth position is less that was on the first SMA wire  30  in the first and second position. As a result, in order for the second SMA wire  32  to transition at generally the same temperatures as the first SMA wire  30  transitioned prior to failing, the second SMA wire must be smaller in diameter to achieve the same relative stress in the wire. Thus, additional SMA wires (second, third, etc.) in the SMA actuator  10 , may be specifically configured and matched the changing spring forces. 
         [0054]    Once the cam mechanism  42  rotates such that the second SMA wire  32  is active (i.e. stressed by the spring  44 ), the SMA actuator  10  may move between the third and fourth positions ( FIGS. 13-14 , respectively) in a similar manner to how the actuator moved between the first and second positions ( FIGS. 11-12 , respectively) when the first SMA wire  30  was active. Thus, the SMA actuator  10  has an automatic redundancy or back-up feature that resets the device&#39;s operational life if the active SMA wire fails. Each redundant wire provided in the actuator restarts the device&#39;s operational life. For example if one wire lasts for 50,000 cycles when it breaks it will be automatically be replaced with a new wire that may last another 50,000 cycles. The SMA actuator  10  also provides a similar stress load in the redundant wire when activated to ensure that the redundant wire transitions at the same temperatures as the primary wire did. 
         [0055]    The SMA actuator  10  may be used in a variety of applications, such as for example, a fluid distribution system. For example, the SMA actuator  10  may be used to control the distribution of a fluid, such as air or another gas or combination of gases, to a compartment, such as a room, automatically, based on the temperature of the fluid in the fluid distribution system. The SMA actuator  10  may control the distribution of the fluid without requiring an outside energy source or action on the part of the room&#39;s occupants. As the temperature of the fluid in the distribution system reaches a predetermined value, the SMA actuator  10  may adjust the system to provide the fluid in a particular direction or pattern. 
         [0056]      FIGS. 15-16  illustrate the SMA actuator  10  as part of an air diffuser  60  for an HVAC system. The depicted air diffuser  60  may be a linear slot, ceiling mounted diffuser. The SMA actuator  10 , however, may be used not only with linear slot diffusers, but with other kinds of ceiling diffusers or side wall diffuser applications. 
         [0057]    The exemplary air diffuser  60  shown may include a housing  62  having an air inlet  64  and an air outlet  66 . The air inlet  66  may be in fluid communication with a source of pressurized air (not shown) and the air outlet  66  may be in fluid communication with a compartment (not shown), such as a room for example. The air diffuser  60  may also include a blade assembly  68  for directing the flow of air out of the diffuser. The blade assembly  68  may be pivotably mounted within the housing  62  about a pivot point  70 . The SMA actuator  10  may mount to an inside surface  72  of the housing  62  by any suitable method, such as by a bracket  74  for example. One or more fasteners  76  may be used to mount the SMA actuator  10  to the bracket  74  and one or more fasteners  78  may be used to mount the bracket  74  to the housing  62 , though any other suitable manner of attaching the actuator and bracket may be used. 
         [0058]    The engagement mechanism  58  of lever  50  may engage a portion  80  of the blade assembly  68  such that movement of the lever  50  moves the blade assembly between a first or heating position ( FIG. 15 ) and a second or cooling position ( FIG. 16 ). The engagement mechanism  58  may include “tongs” that may engage, for example, a straight diffuser blade, or the engagement mechanism may be configured as required to engage different types of diffuser blades. 
         [0059]    As shown in  FIG. 15 , the exemplary blade assembly  68  is in a position such that air flowing through the housing  62  may flow out of the air outlet  66  in a generally perpendicular direction to the outlet, as shown by arrow  82 . For an air diffuser mounted at the top of a wall of a room, this flow pattern is advantageous for heating the room because it forces the heating air downward along the wall. Thus, since warm air rises, forcing the air to the bottom of the room more effectively heats the room. 
         [0060]    To place the diffuser  60  in the heating position, the actuator lever  50  is in the first position or the third position as illustrated in  FIGS. 11 and 13 , respectively. Thus, the SMA wires  30 ,  32  are in the austenite state. The warm air flowing through the housing  62  may be used to heat the SMA wires  30 ,  32  above the austenite finish temperature A F ; thus, the actuator automatically moves the diffuser blade assembly  68  without use of an external power source. 
         [0061]    In  FIG. 16 , the exemplary blade assembly  68  is in a position such that air flowing through the housing  62  is directed around the blade assembly and out of the air outlet  66  generally tangential to the outlet, as shown by arrow  84 . For an air diffuser mounted at the top of a wall of a room, this flow pattern is advantageous for cooling because it forces the cooling air along the ceiling. Thus, since cool air sinks, forcing the air along the ceiling of the room more effectively cools the room. 
         [0062]    To place the diffuser  60  in the cooling position, the actuator lever  50  is in the second position or the fourth position as illustrated in  FIGS. 12 and 14 , respectively. Thus, the SMA wires  30 ,  32  are in the martensite state. The cool air flowing through the housing  62  may be used to cool the SMA wires  30 ,  32  below the martensite finish temperature M F ; thus, the actuator automatically moves the diffuser blade assembly  68  without use of an external power source. 
         [0063]    In an application such as an air diffuser, it is desirable for the air diffuser to switch between the heating position and the cooling position as rapidly as possible. A slow change between the two positions or a pause between the two positions may result in air being directed to an undesirable location within the room, such as for example, directly onto an occupant in the room. 
         [0064]    The SMA actuator  10  and the air diffuser  60  are configured to ensure that when the transition start temperatures M S  and A S  are reached, the SMA wires  30 ,  32  transition completely from one state to the other. This is particularly important when the SMA actuator  10  transitions from the second and fourth positions to the first and third positions, respectively, because it is the force of the contracting SMA wire that moves the SMA actuator  10 . 
         [0065]    The SMA actuator  10  and air diffuser  60  may ensure complete transition of the SMA material by dynamically modifying the stress on the active SMA wire during transition. For example, as the SMA wire  30  transitions to the austenite phase, the SMA actuator  10  and the diffuser  60  are configured to lower the amount of stress on the first SMA wire  30 . As a result of the reduced stress, the austenite finish temperature A F  may actually be lower than the austenite start temperature A S . Thus, once rising temperatures start the first SMA wire  30  transitioning to austenite, the first SMA wire  30  will complete the transition to austenite even if the temperature stops rising or rises very slowly. 
         [0066]    The SMA actuator  10  and the diffuser  60  may accomplish this in a number of ways. For example, as illustrated in  FIGS. 11 and 12 , when the lever  50  is in the second position, the force acting on the first end  54  of the lever from the first SMA wire  30  is generally along the wire. The first end  54  of the lever  50 , however, is angled from the pivot point  52  as illustrated by line X 2  in  FIG. 12 . As the lever  50  rotates counter clockwise, the angle between the first end  54  and the pivot point  52  decreased resulting in the force from the SMA wire being more efficiently transferred to the lever  50 . As a result, the lever  50  is easier to rotate and the effective stress on the first wire  30  is reduced. 
         [0067]    As another example, referring to  FIGS. 15 and 16 , when the exemplary blade assembly  68  is in the cooling position, it is obstructing and redirecting the flow of air through the air diffuser to a greater extent than the position of the blade assembly in the heating position. As a result, when the blade assembly is moving from the cooling position to the heating position, the force of the air onto the blade assembly urges the assembly to the heating position. Thus, the diffuser is configured such that the air aides in the movement of the blade assembly. This aiding force is transferred through the SMA actuator  10  and results in reduced stress on the first SMA wire  30  as it moves the blade assembly  68 . 
         [0068]    The SMA material selected for the SMA wire may be any suitable SMA, such as for example, nitinol. Other SMA alloys may be used and may be selected to provide different temperature actuation ranges, based on availability, or for any other reason without departing from the spirit and scope of the invention. Other SMA alloys include copper/zinc/aluminum, copper/aluminum/nickel, silver/cadmium, gold/cadmium, copper/tin, copper/zinc, indium/titanium, nickel/aluminum, iron/platinum, manganese/copper, iron/manganese/silicon, and other nickel/titanium alloys. SMA alloys are sold, for example, under the brand names Muscle Wires®, Flexinol®, and BioMetal®, which are registered trademarks of Mondo-tronics, Inc., Dynalloy, Inc., and Toki Corporation, respectively. 
         [0069]    The invention has been described with reference to the preferred embodiments. Modification and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.