Patent Publication Number: US-9425014-B2

Title: Circuit interruption device employing shape memory alloy element

Description:
BACKGROUND 
     1. Field 
     The disclosed and claimed concept relates generally to electrical interruption equipment and, more particularly, to a circuit interruption device that employs a shape memory alloy element. 
     2. Related Art 
     Circuit interruption devices of many types are well understood in the relevant art. Among such well-known circuit interruption devices are circuit breakers, vacuum interrupters, ON/OFF switches, and the like without limitation. While circuit interruption devices have been generally effective for their intended purposes, they have not been without limitation. 
     Some applications require a circuit interruption device that is capable of operating in a high current environment, such as where current on the order of 400-500 Amperes is continuously fed. A circuit interruption device suited to such a circuit may potentially be difficult to move between ON and OFF positions. For this reason and for other reasons, such circuit interruption devices have thus sometimes employed devices such as solenoids and other such devices to switch the circuit interruption device to its OFF position in certain predefined circumstances. It is furthermore noted, however, that a solenoid that is suited to open the contacts of a circuit interruption device rated for 400-50 Amperes continuous feed can be bulky and heavy. Such bulk and weight are undesirable in certain applications, such as aerospace applications. It thus would be desired to provide an improved circuit interruption device. 
     SUMMARY 
     According to one aspect, a circuit interruption device includes a support, a set of separable contacts being movable between an OPEN condition and a CLOSED condition, and a first member situated on the support and being movable between an OFF position that corresponds with the OPEN condition and an ON position that corresponds with the CLOSED condition. The movable member is biased toward the first position and has a first surface and a second surface. The circuit interruption device also includes a second member situated on the support and that is movable between an extended position and a retracted position. The second member is biased toward the extended position and has another first surface and another second surface. The circuit interruption device also includes a transport mechanism which includes a shape memory alloy element that is transformable between a first shape and a different second shape responsive to an electrical pulse. In a first configuration of the circuit interruption device, the first member is in the OFF position, the second member is in the extended position, the shape memory alloy element is in its first shape, and the first surface and the another first surface are engaged with one another and are structured to resist movement of the first member away from the OFF position. Responsive to an electrical pulse, the shape memory alloy element is structured to transform into its second shape and to move the first member toward its ON position. In a second configuration of the circuit interruption device, the second member is in the extended position, and the another second surface is engageable with the second surface to resist movement of the first member away from the ON position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the disclosed and claimed concept can be gained from the following Description when read in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of an improved circuit interruption device in accordance with the disclosed and claimed concept; 
         FIG. 2  is a perspective sectional view as taken along line  2 - 2  of  FIG. 1 ; 
         FIGS. 3-5  are elevational sectional views of the circuit interruption device of  FIG. 1  as taken along line  2 - 2  of  FIG. 1  with an operation apparatus and/or a latch apparatus thereof being in different relative positions; 
         FIG. 3A  is an enlarged view of the indicated portion of  FIG. 3 ; 
         FIG. 4A  is an enlarged view of the indicated portion of  FIG. 4 ; and 
         FIG. 5A  is an enlarged view of the indicted portion of  FIG. 5 . 
     
    
    
     Similar numerals refer to similar parts throughout the specification. 
     DESCRIPTION 
     An improved circuit interruption device  4  is depicted generally in  FIGS. 1-5A . As can be seen in  FIGS. 3-5 , the circuit interruption device  4  includes or is at least cooperably connected with a set of separable contacts  6  that are connected with a line conductor  8  and a load conductor  10 . The circuit interruption device  4  is operable to move the set of separable contacts  6  between an OPEN condition that is depicted generally in  FIGS. 3 and 5  and a CLOSED condition that is depicted generally in  FIGS. 2 and 4 . The circuit interruption device  4  is itself movable between an OFF position that is depicted generally in  FIGS. 3 and 5  and an ON position that is depicted generally in  FIGS. 2 and 4 . The OFF position of the circuit interruption device  4  corresponds with the OPEN condition of the set of separable contacts  6 , and the ON position of the circuit interruption device  4  corresponds with the CLOSED condition of the set of separable contacts  6 . As is generally understood in the relevant art, the CLOSED condition of the set of separable contacts  6  causes the line and load conductors  8  and  10  to be electrical connected together. 
     The circuit interruption device  4  can be generally said to include a support  12  upon which are disposed an operation apparatus  16  and a latch apparatus  20 . The operation apparatus  16  can be said to include an operating member  24  that is translatable along a first longitudinal direction  28  between an ON position that is depicted generally in  FIGS. 2 and 4  and an OFF position that is depicted generally in  FIGS. 3 and 5 . Such movements of the operating member  24  between its ON and OFF positions serve to switch the circuit interruption device  4  between its ON and OFF positions. 
     The operation apparatus  16  can further be said to include a return spring  32  that biases the operating member  24  toward the OFF position and to further include a transport mechanism  36 . As will be set forth in greater detail below, the transport mechanism  36  is operable to move the operating member  24  from the OFF position to the ON position responsive to an electrical pulse. 
     The operating member  24  can itself be said to include an elongated rod  40  that is operatively connected with a movable contact of the set of separable contacts  6  as is depicted generally in  FIGS. 3-5 . The operating member  24  further includes an annular flange  44  that protrudes outwardly from the rod  40  and which includes a ramped surface  48  and an abutment surface  52  that are best depicted in  FIGS. 3A, 4A, and 5A . The ramped surface  48  is oriented generally oblique to the first longitudinal direction  28 , and the abutment surface  52  is oriented generally perpendicular to the first longitudinal direction  28 . As employed herein, the expression “oblique” shall refer generally to a relationship that is neither parallel nor perpendicular. The ramped and abutment surfaces  48  and  52  face generally away from one another. 
     The transport mechanism  36  can be stated to include a shape memory alloy element  56  and a heat sink  60 , with the shape memory alloy element  56  having a connection  64  with the operating member  24 , and with the shape memory alloy element  56  having another connection  68  with the heat sink  60 . In the depicted exemplary embodiment, the shape memory alloy element  56  extends about a portion of a perimeter of a pin  72  that is mounted on the support  12 . The heat sink  60  is itself mounted on the support  12  in the depicted exemplary embodiment. 
     The shape memory alloy element  56  is formed of a Single Crystal Shape Memory Alloy (SCSMA) that can be formed from a metallic alloy whose constituents may largely include copper-aluminum-nickel (Cu—Al—Ni) or other appropriate alloy. An SCSMA has various advantages over a conventional Shape Memory Alloy (SMA), and thus the shape memory alloy element  56  is desirably formed of an SCSMA. Advantages of an SCSMA include significantly greater strain recovery, 9% versus 3% for an SMA. Further advantages of an SCSMA over an SMA include true constant three deflection, and very narrow loading hysteresis and recovery which are generally 100% repeatable and complete. An SCSMA additionally has a transition temperature range that may be, for instance, in the range of −200° C. to +250° C., which is a greater transition range than a conventional SMA. Other advantages are known in the general art. It is also noted, however, that the shape memory alloy element  56  may be formed from an SMA depending upon the needs of the particular application. 
     As is generally understood in the art, a shape memory alloy material such as a conventional SMA or an improved SCSMA is typically formed to have some type of an original shape. The SMA or the SCSMA can thereafter be deformed by bending, stretching, and the like into any of a variety of shapes while it remains at a temperature that is less than its transition temperature. Upon heating the SMA or the SCSMA to its transition temperature, however, the shape memory alloy transforms from its deformed shape back into to its original shape. Upon cooling of the shape memory alloy below its transition temperature, it may return to the deformed shape. 
     Accordingly, the shape memory alloy element  56  employed herein is movable between an original shape and a deformed shape. The shape memory alloy element  56  returns to its original shape in response to heating, which is provided by an electrical pulse applied to the shape memory alloy element  56 . More particularly, the shape memory alloy element  56  is, in the depicted exemplary embodiment, an elongated structure whose length changes when it moves between the deformed shape and the original shape. The original shape is of an elongated configuration and is of a relatively shorter length whereas the deformed shape is likewise of an elongated configuration but of a relatively longer length. When an electrical pulse is applied to the shape memory alloy element  56  and heats it above its transition temperature, the shape memory alloy element  56  shortens from its relatively longer deformed shape to its relatively shorter original shape. As will be set forth in greater detail below, such shrinking or reduction in the length of the shape memory alloy element  56  that is occasioned by the electrical pulse applied thereto causes the operating member  24  to be moved from its OFF position to its ON position. 
     In the depicted exemplary embodiment, the shape memory alloy element  56  is an elongated fiber formed of an SCSMA. When the shape memory alloy element  56  is heated by the aforementioned electrical pulse applied thereto, the length of the shape memory alloy element  56  shrinks by approximately 9%, which is a change in length that is sufficient to move the operating member  24  from its OFF position to its ON position, which will be described in greater detail below. 
     The exemplary heat sink  60  is formed from aluminum or other appropriate thermally conductive material and is configured to rapidly cool the shape memory alloy element  56  to a temperature below its transition temperature subsequent to the application of the electrical pulse. The heat sink  60  does so in a generally understood fashion by shunting heat away from the shape memory alloy element  56 . The heat sink  60  is desirably configured to have a heat shunting capacity that is great enough to provide sufficient heat shunting to cool the shape memory alloy element  56  to a temperature below its transition temperature despite repeated operation of the circuit interruption device  4 . That is, the heat sink  60  has a sufficient heat shunting capacity that it will continue to cool the shape memory alloy element  56  below its transition temperature in an environment of repeated applications of electrical pulses to the shape memory alloy element  56  and dissipation of the heat generated therefrom to the heat sink  60 . 
     The latch apparatus  20  can be generally said to include a solenoid  76  and a biasing element  80  that are both situated on the support  12 . The solenoid  76  is a miniature solenoid and includes an electrical coil  84  such as a close coil and plunger  88 . The plunger  88  is movable along a second longitudinal direction  90  between an extended position as is depicted generally in  FIGS. 2, 3, 3A, 4, and 4A  and a retracted position as is depicted generally in  FIGS. 5 and 5A . It is noted that  FIGS. 2, 3, 3A, 4 , and  4 A further depict in phantom lines the plunger  88  in its retracted position in order to illustrate the distance of movement between the extended and retracted positions. In the depicted exemplary embodiment, the first and second longitudinal directions  28  and  90  are substantially orthogonal to one another although other positional relationships can be employed depending upon the needs of the particular application. In the depicted exemplary embodiment, the coil  84 , when energized, causes the plunger  88  to move to its retracted position. The biasing element  80  biases the plunger  88  toward the extended position. 
     The plunger  88  can be said to include a latching element  92  at an end thereof that interacts with the flange  44  of the operating member  24 . The latching element  92  includes an angled surface  94  and an engagement surface  98  that face generally away from one another. In the depicted exemplary embodiment, the angled surface  94  is oriented oblique to both the second longitudinal direction  90  and the first longitudinal direction  28 . Further in the depicted exemplary embodiment, the exemplary engagement surface  98  is oriented substantially perpendicular to the first longitudinal direction  28  and generally parallel with the second longitudinal direction  90 . It can be seen that the abutment surface  52  is likewise oriented. 
     The circuit interruption device  4  in  FIG. 3  can be generally said to be in a first configuration which corresponds with the OFF position of the circuit interruption device  4 . The circuit interruption device  4  in  FIGS. 2 and 4  can be generally said to be a second configuration which corresponds generally with the ON position of the circuit interruption device  4 . Furthermore, the circuit interruption device  4  is movable between the first and second configurations. 
     More particularly, and as can be generally understood from  FIGS. 3 and 3A , when the circuit interruption device  4  is in the first configuration, the shape memory alloy element  56  is in its relatively longer deformed shape, the operating member  24  is in its OFF position, the set of separable contacts  6  are in their OPEN condition, and the plunger  88  is in its extended position due to the solenoid  76  being de-energized and also due to the biasing element  80  biasing the plunger  88  toward the extended position. In such a situation, the ramped surface  48  of the flange  44  and the angled surface  94  of the latching element  92  are engaged with one another. Such engagement of the ramped and angled surfaces  48  and  94  and the bias of the biasing element  80  to maintain such engagement helps to retain the operating member  24  in its OFF position despite vibration, acceleration, and the like. For the sake of completeness, it is reiterated that the return spring  32  biases the operating member  24  toward the OFF position, which further helps to retain the operating member  24  and the circuit interruption  4  in the OFF position. It thus can be understood that when the circuit interruption  4  is in its OFF position, the interaction between the latching element  92  and the flange  44  of the operating member  24  helps to retain the circuit interruption device  4  in its OFF position. 
     When it is desired to switch the circuit interruption device  4  from its OFF position to it ON position, an electrical pulse is applied to the shape memory alloy element  56  which, as set forth above, heats the shape memory alloy element  56  and causes it to transform from its relatively longer deformed shape to its relatively shorter original shape. Such shrinking or contraction or shape transformation by the shape memory alloy element  56 , i.e., changing its length from the relatively longer length of the deformed shape to the relatively shorter length of the original shape, causes a tensile force to be applied to the operating member  24 . Such tensile force is applied to the operating member  24  in the first longitudinal direction  28  and generally in the upward direction from the perspective of  FIGS. 3 and 3A . The tensile force is of sufficient magnitude to overcome the bias of the return spring  32  and to further overcome the bias of the biasing element  80  by causing the ramped and angled surfaces  48  and  94  to slide along one another and to cause the plunger  88  to be moved from its extended position toward the retracted position. In addition to overcoming the bias of the biasing element  80  by such sliding movement between the ramped and angled surfaces  48  and  94 , the tensile force from the shape memory alloy element  56  additionally overcomes static and dynamic friction between the ramped and angled surfaces  48  and  94 . 
     As mentioned above, the length of the shape memory alloy element  56  shrinks by approximately 9% when the shape memory alloy element  56  is heated by the electrical pulse. In the depicted exemplary embodiment, the set of separable contacts  6  have a nominal arc gap of 0.038 inches in the OPEN condition. Moreover, the movable portion of the set of separable contacts  6  is additionally movable with respect to the operating member  24  along the first longitudinal direction  28  to provide for an over-travel and/or wear allowance. As such, the total exemplary movement of the operating member  24  along the first longitudinal direction  28  between the ON and OFF positions is 0.053 inches. Therefore, using wire that contacts 9% would require 0.589 inches of wire length to achieve the desired total movement. In the depicted exemplary embodiment, the wire that forms the shape memory alloy element  56  is of a diameter on the order of 0.020 inches. Multiple wires twined together can be used to increase force with the same total movement. 
     Once the tensile force applied by the shape memory alloy element  56  to the operating member  24  moves the plunger  88  sufficiently toward the retracted position that the ramped and angled surfaces  48  and  94  are no longer engaged with one another, i.e., they are disengaged, the contraction of the shape memory alloy element  56  and the resultant tensile force applied to the operating member  24  cause the operating member  24  to be translated along the first longitudinal direction  28  in the upward direction from the perspective of  FIGS. 3 and 4  until the operating member  24  is in the ON position that is depicted generally in  FIGS. 4 and 4A . In such a situation, the flange  44  has moved in the upward direction from the perspective of  FIGS. 3-4A  sufficiently that the flange  44  has cleared the latching element  92 , and the biasing element  80  is thus able to move the plunger  88  and the latching element  92  thereon to the extended position that is depicted generally in  FIGS. 4 and 4A . In such a condition, the engagement surface  98  of the latching element  92  is situated with respect to the abutment surface  52  such that the abutment and engagement surfaces  52  and  98  are engageable with one another and serve to resist the operating member  24  from moving away from the ON position to the OFF position. 
     It is particularly noted that  FIG. 4A  depicts the flange  44  in a condition wherein the shape memory alloy element  56  is in its relatively shorter original shape, such as during application of the electrical pulse or immediately thereafter and prior to the cooling of the shape memory alloy element  56  that is afforded by the heat sink  60 . As such, the abutment surface  52  is depicted as being spaced slightly from the engagement surface  98 . Upon cooling of the shape memory alloy element  56  below its transition temperature, the shape memory alloy element  56  will return toward its relatively longer deformed shape. This will permit the return spring  32  to bias the operating member  24  in the generally downward direction from the perspective of  FIGS. 4 and 4A  until the abutment surface  52  engages the engagement surface  98 . In this condition, the operating member  24  and the circuit interruption device  4  remain in the ON position. 
     It thus can be understood that the electrical pulse which is applied to the shape memory alloy element  56  causes the shape memory alloy element  56  to transition from its deformed shape to its original shape and to thereby move the operating member  24  and the circuit interruption device  4  to the ON position. In such a position, the interaction between the flange  44  and the latching element  92  and, more particularly, the interaction between the abutment surface  52  and the engagement surface  98 , assist in retaining the circuit interruption  4  in its ON position. This can be said to be a second configuration of the circuit interruption device  4 . Advantageously, since the solenoid  76  is in its de-energized condition when the circuit interruption device  4  is in its ON position as is depicted generally in  FIGS. 4 and 4A , the solenoid  76  itself consumes no power to maintain the circuit interruption device  4  in its ON position. Rather, the circuit interruption device  4  is retained in its ON position via interaction between the abutment and engagement surfaces  52  and  98  and with the solenoid  76  being in a no-load or de-energized condition, which advantageously saves electrical power. 
     When it is desired to move the circuit interruption device  4  from its ON position that is depicted generally in  FIGS. 4 and 4A , the circuit interruption device  4  can be moved from its ON position to its OFF position by briefly energizing the coil  84  of the solenoid  76  to cause the plunger  88  to move from its extended position of  FIGS. 4 and 4A  to its retracted position of  FIGS. 5 and 5A . Such movement of the plunger  88  to the retracted position of  FIGS. 5 and 5A  takes the engagement surface  98  out of the direction of travel of the flange  44  and its abutment surface  52  and thereby permits the return spring  32  to bias the operating member  24  to its OFF position. If, prior to the movement of the plunger  88  from the extended position to the retracted position the abutment and engagement surfaces  52  and  98  were engaged with one another, such as would occur if the shape memory alloy element  56  has cooled sufficiently to return it to its relatively longer deformed shape via shunting of heat therefrom by the heat sink  60 , such movement by the plunger  88  to the retracted position will involve overcoming the static and dynamic friction between the abutment and engagement surfaces  52  and  98  and will cause the abutment and engagement surface  52  and  98  to become disengaged from one another. 
     It is understood that  FIGS. 5 and 5A  depict the circuit interruption device  4  in its OFF position while the solenoid  76  is energized and the plunger  88  is in its retracted position. When the coil  84  of the solenoid  76  is de-energized, the biasing element  80  will return the plunger  88  and its latching element  92  toward the extended position, which will cause the angled surface  94  to ride along and engage the abutment surface  52  as is depicted generally in  FIGS. 3 and 3A , which place the circuit interruption device  4  back in its first configuration as described above. 
     It thus can be seen that the circuit interruption device  4  is movable from its OFF position to its ON position as a result of an electrical pulse applied to the shape memory alloy element  56 . After application of such an electrical pulse to the shape memory alloy element  56 , the latching element  92  and the flange  44  cooperate with one another to retain the operating member  24  and thus the circuit interruption device  4  in the ON position while the coil  84  of the solenoid  76  is in a no-load state. The circuit interruption device  4  in its ON position can then be returned to its OFF position by electrically pulsing or energizing the coil  84  of the solenoid  76 , which causes the latching element  92  and the flange  44  to be removed from interaction with one another sufficiently that the return spring  32  can move the operating member  24  and thus the circuit interruption device  4  to the OFF position. Moreover, and as set forth above, when the coil  84  of the solenoid  76  is then de-energized, the biasing element  80  returns the latching element  92  into engagement with the flange  44  whereby such structures retain the circuit interruption device  4  in its OFF position, with the solenoid  76  again being in a no-load state. In such a position, the shape memory alloy element  56  is likewise in a no-load state. 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the an that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.