Abstract:
An airflow control device has a fixed damper element and a movable damper element. Shape memory wires are connected to the fixed damper element and the movable damper element. The shape memory wires are alternately electrified to cause the contraction thereof to move the movable damper element in opposite directions. A heater can be provided along with the damper elements to overcome frost buildup in cold environments, such as refrigeration systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims benefit to U.S. Provisional Patent Application Serial No. 60/373,040, filed on Apr. 16, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to airflow control devices, and, more particularly to dampers for regulating the flow of air between one compartment and another compartment, such as for example, between a freezer section and a refrigerated section of a refrigerator.  
         BACKGROUND OF THE INVENTION  
         [0003]    There are many known airflow control devices for regulating the flow of air from one area to another area. In regards to refrigerators in particular, known refrigerator arrangements utilize a compressor refrigeration system for chilling the environment within the freezer compartment of the refrigerator. The refrigerated food compartment of the refrigerator is cooled by moving cold air from the freezer compartment into the refrigerated compartment. An airflow damper is provided between the refrigerated compartment and the freezer compartment to regulate the amount of cold air that is allowed to pass from the freezer compartment to the refrigerated compartment.  
           [0004]    It is known to provide some type of user input for regulating and controlling the operation of the airflow damper. In lower end refrigerators, the damper mechanism commonly is a simple slider type damper having a fixed opening and a slide thereover. The slide portion is connected to a knob via a rod or other link mechanism. Adjustment of the knob position moves the slider mechanism to adjust the effective size of the opening through the damper, to regulate, at least to some limited extent, the amount of cold air allowed to enter the refrigerated compartment from the freezer compartment. The slider remains in the selected position until moved again by readjustment of the knob position. While some minimal control results, the refrigerated compartment is not truly temperature controlled, and will become colder or warmer under various operating and use conditions of the refrigerator. For example, if the refrigerated compartment is opened frequently and the damper is positioned for substantially restricted flow, insufficient airflow from the freezer compartment will result in the refrigerated compartment becoming warm. Conversely, if the refrigerated compartment is opened only infrequently, the temperature therein may approach the temperature of the freezer compartment with a fixed opening damper as described. Advantages of this type of damper include simplicity and inexpensive cost. A disadvantage is the relative inaccuracy of the temperature control provided thereby.  
           [0005]    In a somewhat more functional design, the damper is a mechanically operated device connected to a thermostat. Refrigerant in the damper mechanism provides operational control. As the temperature in the refrigerated compartment changes, the refrigerant will expand or contract. Thus, if the refrigerated compartment door is opened frequently, or left open for long periods of time such that the compartment warms, the refrigerant will expand, causing the damper to open. As the refrigerated compartment cools, the refrigerant contracts, in turn causing the damper to close. Thus, damper opening and closing is controlled in relation to the actual temperature in the refrigerated compartment. Disadvantages of systems of this type include the cost and complexity of the system, wider than desirable temperature swings in the refrigerated compartment, and the disadvantage of using a toxic fluid in the control system.  
           [0006]    In general, more energy efficient refrigerators have electronically controlled refrigerated and freezer compartments. A micro-controller monitors the refrigerator use and compartment temperatures, and controls airflow between the compartments for precisely regulated temperature in the refrigerated compartment. An electrically actuated damper receives a signal from the micro-controller, determining when to open and close the damper. User input adjusts the relative temperature level to which the refrigerated compartment is controlled. Drawbacks to known systems of this type include the relative complexity of the system and the cost associated with it. The electrically actuated damper is typically a motor driven device consisting of a gearbox and capacitors. The motor and gearbox are relatively robust to withstand potential frost or freezing conditions in the damper unit. The motor has sufficient power along with the gearbox to break loose the moveable components, if frosting or freezing occurs. Nevertheless, severe frost over can cause the damper to malfunction and can result in damage. Systems of this type are undesirably large, reducing the space available for storing food.  
           [0007]    What is needed in the art is a refrigerator damper capable of accurately regulating the refrigerated compartment temperature, yet which is simple, compact and inexpensive to manufacture. Additionally, new, inexpensive and reliable methods to control frost over of the damper are needed.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention meets the aforementioned needs and other needs by providing according to one aspect thereof an airflow control device using shape memory wire to open and close a damper. For particularly cold applications, such as in a refrigerator, according to another aspect of the present invention there is provided in association with the airflow control device a heater to control frost over or freeze up.  
           [0009]    In one form thereof, the present invention provides a damper with a first damper element and a second damper element, each having an opening therethrough. One of the damper elements overlies the other of the damper elements. At least one of the damper elements is movable relative to the other. A shape memory member adapted to contract in length upon application of an electric current thereto, and to elongate upon interruption of the current thereto, is attached to the at least one of the elements for causing movement of the at least one element by contraction of the member. An electric current source is electrically connected to the member for selectively applying electrical current to the member. When the electrical current is cut-off, the shape memory member effectively cools, thereby allowing the member the ability to return to its original shape.  
           [0010]    In another form thereof, the present invention provides a refrigerator damper with a fixed damper element having a first plurality of openings therethrough, and a movable damper element juxtaposed over the fixed element and having a second plurality of openings therethrough. The movable damper element is movable between a first position in which the second plurality is not aligned with the first plurality and a second position in which the second plurality of openings is in substantial alignment with the first plurality of openings. A shape memory wire has one end attached to the movable damper and a second end attached to the fixed damper element to cause movement of the movable damper upon heating of the wire.  
           [0011]    In yet another form thereof, the present invention provides a method for controlling airflow between two compartments, such as, for example, of a refrigerator. The method has steps of providing a movable damper element having at least one opening therethrough, the damper element being movable between first and second positions providing different airflow through the element; providing a shape memory member attached to the damper element, the member being responsive to a temperature thereof to change a physical dimension thereof; providing an electric circuit electrically connected to the member; and moving the movable damper element by selectively directing an electric current to the shape memory member or interrupting an electric current directed to the shape memory member in response to a need to adjust the position of the movable damper element.  
           [0012]    An advantage of the present invention is providing a simple yet reliable damper that is easy to install and reliable in operation for an extended useful lifetime.  
           [0013]    Another advantage of the present invention is providing a damper that is compact and relatively inexpensive to install and operate.  
           [0014]    Yet another advantage of the present invention is providing a damper having simple yet reliable heater means for eliminating frost over and insuring reliable damper operation in cold environments, such as found in a refrigerator.  
           [0015]    Still another advantage of the present invention is providing a strong, compact activation mechanism that is easy to control and operate.  
           [0016]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a perspective view of a damper or airflow control device according to the present invention, illustrating the damper in a closed position;  
         [0018]    [0018]FIG. 2 is a plan view of the damper shown in FIG. 1, but illustrating the damper in an open position allowing airflow there through;  
         [0019]    [0019]FIG. 3 is a cross sectional view of the damper shown in FIG. 1, taken along line  3 - 3  of FIG. 1;  
         [0020]    [0020]FIG. 4 is a cross sectional view of the damper shown in FIG. 2, taken along line  4 - 4  of FIG. 2;  
         [0021]    [0021]FIG. 5 is an enlarged cross sectional view of a detent mechanism in the damper of the present invention;  
         [0022]    [0022]FIG. 6 is a cross sectional view similar to that of FIG. 5, but illustrating the detent mechanism in a different stage of operation from that shown in FIG. 5;  
         [0023]    [0023]FIG. 7 is an enlarged cross sectional view similar to that of FIGS. 5 and 6, but illustrating the detent mechanism in yet another stage of operation;  
         [0024]    [0024]FIG. 8 is a cross sectional view of a modified form of the damper of the present invention, the view being similar to that shown for the first embodiment in FIG. 4; and  
         [0025]    [0025]FIG. 9 is schematic view of a control system for the damper of the present invention. 
     
    
       [0026]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use herein of “including” and “comprising”, and variations thereof, is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items and equivalents thereof.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    Referring now more specifically to the drawings and to FIG. 1 in particular, numeral  10  designates a damper in accordance with the present invention. Damper  10 , as shown and described below, is provided in an airflow duct between a refrigerated compartment and a freezer compartment of a refrigerator. Those skilled in the art will understand that damper  10  may operate directly in an opening provided in a wall between the refrigerator and freezer compartments, or damper  10  may operate in a duct directing airflow from the freezer compartment to the refrigerated compartment. Flow through damper  10  may be natural airflow, or flow therethrough may be induced by a fan or other air moving device. It should be noted that although the invention is described in connection with a refrigerator, the invention is capable of use in other airflow control applications, and a refrigerator is merely shown and described as an example of one such application.  
         [0028]    Damper  10  includes a first damper element in the nature of a fixed frame  12  having a base  14  and peripheral guides  16  disposed about base  14 . In the exemplary embodiment illustrated, base  14  is provided with guides  16  along elongated sides and one end thereof. Base  14  is provided with a plurality of airflow openings  18  (FIG. 3) which allow air to pass from one side of base  14  to the opposite side of base  14 . Openings  18 , only some of which are identified with the reference number  18  in the drawings, are shown as relatively narrow, elongated openings, but other configurations can also be used.  
         [0029]    Damper  10  is further provided with a second damper element in the nature of a slider  20  (FIG. 2) overlying base  14 , and moveable relative to base  14  within the confines of guides  16 . Slider  20  fits relatively close between guides  16  for controlling the relative movement of slider  20  with respect to base  14 . Other types of guide mechanisms including tracks and the like can be used.  
         [0030]    Slider  20  is provided with a plurality of airflow openings  22  (FIG. 3) therethrough. Airflow openings  22 , only some of which are identified with the reference number  22  in the drawings, are similar in size, shape and relative positioning to airflow openings  18 . Slider  20  is movable relative to base  14  such that airflow openings  22  therein can be positioned in substantial alignment with airflow openings  18  in base  14 , or can be positioned in misalignment with airflow openings  18 . Thus, as illustrated in FIG. 3, when misaligned, airflow through damper  10  is inhibited. As illustrated in FIG. 4, when airflow openings  22  are aligned with airflow openings  18 , air can flow through damper  10  so that chilled air from a freezer compartment of a refrigerator can flow through damper  10  to the refrigerated compartment of the refrigerator, thereby cooling the refrigerated compartment.  
         [0031]    Movement of slider  20  relative to base  14  occurs through operation of an actuator mechanism  30 . Actuator mechanism  30  includes first and second shape memory members  32  and  34  in the nature of wires anchored between frame  12  and slider  20 . Thus, shape memory wire  32  includes a first end connected to a first anchor  36  on frame  12  and a second end connected to a first second anchor  38  on slider  20 . Similarly, shape memory wire  34  includes a first end connected to a second anchor  42  on frame  12  and a second end connected to second anchor  40  on slider  20 .  
         [0032]    Shape memory wire is a known material, referred to as shape memory alloys, such as nickel titanium alloy which, when heated contracts in length. Transition is rapid at the transition temperature, which is determined by the ratio of nickel to titanium in the alloy. Wires of shape memory alloy can be made to contract an amount based on a percentage of the relaxed wire length, such as, for example, 6-10%. Shape memory alloys commonly have a high electrical resistance, and can be heated to the transition temperature by passing an electric current therethrough. By controlling a flow of electricity through shape memory wires  32  and  34 , accurate operation thereof is made to cause the wires to selectively contract, thereby moving slider  20  in one direction or another. Upon interruption of the flow of electric current through shape memory wires  32  or  34 , rapid cooling occurs and elongation results, thereby allowing slider  20  to be pulled by the other shape memory wire  32  or  34  in the opposite direction.  
         [0033]    Under proper operating conditions, the shrinkage factor of shape memory wire is accurate and repeatable at the transition temperature over a prolonged life (more than one million cycles). A bias force is provided to the wire in the direction of elongation, to assist in returning the wire to the relaxed state and dimensions thereof. While springs can be used, with wires  32  and  34  contracting in opposite directions, a bias force that is passive in the contracted direction after completion of movement is desirable.  
         [0034]    According to one embodiment of the present invention, a mechanical assist in the way of detent mechanism  50  (FIGS. 5, 6 and  7 ) is provided for supplying mechanical assist or biasing force to the final movement of each wire  32  and  34  in its direction of elongation. Detent mechanism  50  includes first and second cavities  52  and  54  provided in frame  12 , such as in one of the elongated side guides  16  along which slider  20  is moved. A ball  56  urged by a spring  58  from a slot  60  in slider  20  is provided to operate between first and second cavities  52  and  54 . Thus, as slider  20  moves between the fully opened and fully closed positions of damper  10 , ball  56  rolls between first cavity  52  and second cavity  54 . As ball  56  rolls into either first cavity  52  or second cavity  54 , the slopped side walls of the cavity function together with the outwardly urged ball  56  to provide a biasing force or mechanical assist for final movement of slider  20  in one or the other direction. First and second cavities  52  and  54  can be shaped as needed for providing the degree and type of mechanical assist desired. Thus, cavities  52  and  54  can be provided of the substantially spherical shapes shown for receiving ball  56  therein, or more gently sloping entrance and exit surfaces can be provided for each cavity  52  or  54 . When ball  56  is seated within cavity  54  or cavity  56 , damper  10  is latched in either its closed or opened position. Other assist mechanisms may be used in accordance with the principles of the present invention.  
         [0035]    Although the shape memory members  32  and  34  can be designed and configured to accommodate frost build up, according to one aspect of the present invention, to minimize frost that could result in freeze-up of damper  10 , a heater  62  (FIG. 9) is provided. In one advantageous configuration for heater  62 , a positive temperature co-efficient (PTC) layer  64  (FIG. 8) is provided between base  14  and slider  20 . PTC layer  64 , as known to those skilled in the art, is caused to heat upon receipt of an electric current. By providing a heater layer  64  between base  14  and slider  20 , any frost build-up or freezing is heated, thereby loosening slider  20  relative to base  14 , and enabling sliding movement of slider  20  over base  14 . Alternatively, blanket style heaters or heating rods can be used in accordance with the principles of the present invention.  
         [0036]    In yet another advantageous embodiment for heater  62 , one or the other of base  14  or slider  20 , or a part thereof, can be made of PTC material.  
         [0037]    Also as illustrated in FIG. 8 (as well as FIG. 4), base  14  and slider  20  are provided with oppositely angled mating surfaces, or draft, so that the surfaces are in contact with each other only in an extreme position of slider  20 . Through out movement of slider  20 , in either direction, the surfaces are spaced from each other, and sliding resistance of the surfaces against each other is reduced. Accordingly, although not clearly shown, it should be understood that when in the open position, base  14  and slider  20  are preferably slightly spaced apart over a portion of their opposing surfaces.  
         [0038]    [0038]FIG. 9 illustrates a general schematic of an electric circuit  70  by which damper  10  can be operated. A controller  72  is provided as a main controller for operation of the refrigerator. Controller  72  controls starting and stopping of numerous refrigerator functions. In that regard, controller  72  communicates with a refrigerated compartment temperature sensor  74  and a freezer compartment temperature sensor  76  to ascertain the temperature existing in each compartment. User input information is provided to controller  72  relative to the desired freezer compartment and refrigerated compartment temperature levels and, based on existing conditions and use, controller  72  can actuate a compressor  78  or other components of a refrigeration system to cause cooling in the freezer compartment. As necessary, controller  72  also actuates damper  10  to enable or disable cold airflow from the freezer compartment to the refrigerated compartment.  
         [0039]    For actuating and de-actuating shaped memory members  32  and  34 , limit switches  80  and  82  (FIG. 1) are provided in a circuit between controller  72  and shape memory members  32  and  34 . Controller  72  is further operated to actuate defrost heater  62  of damper  10 , or a main defrost unit  84  for the main refrigerator compartments. The function of heater  62  can be on a periodic schedule in conjunction with or separately from main defrost unit  84  or, more advantageously heater  62  can be actuated to briefly heat damper  10  before actuation of either shape memory member  32  or  34 . Another function of the limit switches  80  and  82  is that they can indicate the state of the damper  10  (i.e., open or closed) when the system is faced with a power failure. In this way, the system or controller  72  knows the actual state of the damper  10  and cannot incorrectly determine that the damper  10  is opened when it is actually closed, or closed when it is actually opened.  
         [0040]    While damper  10  has been shown and described herein as generally rectangular in shape, it should be understood that damper  10  can be of other shapes as well. For example, damper  10  can be generally round, with a movable damper element rotatable about an axis relative to a fixed damper element. Further, while described herein as operable between freezer and refrigerated compartments of a refrigerator, a damper including the principles of operation of the present invention can be used for controlling flow therethrough between other compartments or drawers within a refrigerator, and in devices other than a refrigerator, such as, for example, other appliances, automobile air heating and/or cooling systems, and other airflow control devices.  
         [0041]    Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.  
         [0042]    Various features of the invention are set forth in the following claims.