Abstract:
A damper suitable for use in a refrigerator provides for linear motion of a damper plate toward and away from a damper seat. The damper plate may be driven by an axial lead screw attached to a small DC motor and may employ a non-foam gasket to reduce water absorption and possible formation of obstructing ice.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional application 60/547,920 filed Feb. 26, 2004 hereby incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     --  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates to an air damper for control of the flow air, for example, between compartments of a refrigerator, and in particular to an improved air damper with linear valve travel and a low cost electric actuator.  
         [0004]     A household refrigerator may provide for a number of different compartments with different temperature and humidity conditions. A convenient method of creating these multiple environments employs one or more dampers controlling the flow of air flow between the compartments.  
         [0005]     Dampers of this type may use a pivoting door or flapper that is opened and closed by a motor or other actuator. The actuators are normally limited to relatively low wattage devices, for example, low voltage DC motors, to reduce cost, promote energy efficiency, and to minimize heat dissipation by the actuator within the refrigerator.  
         [0006]     The operating environment of the dampers, positioned between chambers with different air temperatures and humidities, can produce condensation and icing on the damper components. Ice can interfere with the pivoting action of the flapper by encrusting the pivot point of the flapper or by causing adhesion between the outboard portion of the flapper and the rim of the damper opening where small amounts or resistance can require large torques to overcome.  
         [0007]     In order to eliminate leakage around the flapper, the flapper may include a gasket compressed between the flapper and the damper opening. This gasket is often a highly compliant foam material sealing with low compression forces. The foam gasket accommodates the varying forces, and possibly varying separation, between the flapper and damper opening caused by the pivoting action of the flapper.  
         [0008]     A drawback to foam gaskets is that they may absorb water, freeze, and become less compliant or adhered to the damper opening, as described above. Further, foam gaskets may become brittle with time losing their compliance and sealing ability.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The present invention provides a damper having a damper plate that moves linearly rather than with a pivoting motion to cover or uncover the opening of a damper seat. The linear motion may be provided by a lead screw driven by a small DC motor. The linear motion and the mechanism that produces it are more resistant to the effect of icing and permits the use of improved gasketing material. The lead screw mechanism may incorporate springs to prevent jamming of the damper plate against stops when the device is operated with open loop control as is typical in appliances.  
         [0010]     Specifically, the present invention provides an electrically actuated damper providing a motor with an axial lead screw. A damper plate has an attached threaded portion engaging the lead screw. A housing provides an air passageway through a damper seat and supports the damper plate for movement with the lead screw to cover and uncover the damper seat when the lead screw is rotated in a first and second direction, respectively.  
         [0011]     Thus, it is one object of at least one embodiment of the invention to provide a simple mechanism for producing linear motion in a damper plate and one which may provide relatively high opening and closing forces that are not diminished by the lever action found in a typical flapper design.  
         [0012]     The motor may be a permanent magnet DC brush motor having an operating voltage of less than 12 volts.  
         [0013]     Thus, it is another object of at least one embodiment of the invention to provide a simple damper mechanism that works well with low wattage electric motors. The lead screw provides mechanical advantage necessary to open the damper against limited icing without the need for complex gear trains or the like.  
         [0014]     The damper may include a gasket formed from a material without air cells as part of the damper plate and/or damper seat.  
         [0015]     Thus, it is another object of at least one embodiment of the invention to provide a damper that provides more uniform closure of the damper plate against the damper seat avoiding the necessity of using a highly compliant foam gasket.  
         [0016]     The gasket may be an elastomeric material cantilevered in radial extension at the periphery of the damper plate.  
         [0017]     Thus, it is another object of at least one embodiment of the invention to provide sealing with elastomeric material that is flexible but relatively resistant to compression.  
         [0018]     The axial lead screw may have external threads and the threaded portion of the damper plate may be a collar attached to the damper plate with internal threads fitting about the axial lead screw.  
         [0019]     Thus, it is another object of at least one embodiment of the invention to provide a mechanism that is more resistant to icing than gears. The advancing collar may clean off a light coating of ice from the lead screw.  
         [0020]     The collar may include key surfaces fitting within a keyway preventing rotation of the damper plate. The keyway may be of substantially smaller radial extent than the damper plate.  
         [0021]     Thus, it is another object of at least one embodiment of the invention to prevent rotation of the threaded portion of the damper plate using a small area keyway offering limited area for icing.  
         [0022]     The keyway may be open at two axial ends so that movement of the collar through the keyway may eject accumulated ice.  
         [0023]     Thus, it is another object of at least one embodiment of the invention to prevent ice from being compacted within the keyway.  
         [0024]     The collar may be positioned at least partially within the keyway at extreme positions of the collar.  
         [0025]     It is therefore another object of at least one embodiment of the invention to prevent the formation of ice obstructions that must be dislodged by shearing the ice.  
         [0026]     The housing and damper plate may be thermoplastic material.  
         [0027]     Thus, it is another object of at least one embodiment of the invention to provide an inexpensive means of fabricating parts from a material that is resistant to moisture and that has some natural lubricity.  
         [0028]     The lead screw may be stainless steel.  
         [0029]     It is thus another object of at least one embodiment of the invention to provide a high tolerance, low friction lead screw material resistant to ice adhesion.  
         [0030]     The damper may include a stop for limiting motion of the damper plate in uncovering the damper seat and further including at least one spring biasing the damper plate away from the stop.  
         [0031]     It is thus another object of at least one embodiment of the invention to prevent momentum of the damper plate toward the stop from jamming the damper plate when driven by a motor operated to stall. By dissipating energy into the spring, the damper may be operated without limit switches or the like reducing the cost of the system.  
         [0032]     The spring may be a helical compression spring fitting coaxially about the axial drive shaft between the stop and the damper plate.  
         [0033]     Thus, it is another object of at least one embodiment of the invention to provide a simple method for supporting a spring that requires no additional structure.  
         [0034]     The motor may include a series, current-limiting resistor allowing the motor to operate in stall condition without damage.  
         [0035]     It is thus another object of at least one embodiment of the invention to provide the ability to use small DC brush motors in an open loop configuration without damage to the motor.  
         [0036]     These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]      FIG. 1  is a perspective, exploded view of the damper of the present invention showing a motor for turning an axial lead screw to move a damper plate against a damper seat formed in a housing; and  
         [0038]      FIG. 2  is a cross-section along lines  2 -- 2  of  FIG. 1  showing springs for use in preventing jamming of the damper plate when driven to either extreme within the housing. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0039]     Referring now to  FIGS. 1 and 2 , the damper  10  of the present invention may provide a generally rectangular housing  12  having a rear housing portion  14  and a front housing portion  16  fitting together to enclose a volume  18  through which air may flow in a generally axial direction  36 . The front housing portion  16  and rear housing portion  14  are held together by means of laterally extending teeth  20  on the sides of the front housing portion  16  that are engaged by corresponding axially extending hasps  22  on the sides of rear housing portion  14  or by welding or other similar method.  
         [0040]     In use, the housing  12  blocks an opening between two compartments between which airflow must be controlled, for example, in a refrigerator. Front housing portion  16  provides a generally circular air passage  24  on its front rectangular face  26  whereas rear housing portion  14  includes a generally rectangular air passage  28  on its rear rectangular face  30 . In the preferred embodiment, each air passage  24  may be approximately 3 square inches in area.  
         [0041]     Supported coaxially within air passage  24  is a front bearing  32  held by a spider support  34 . The spider support  34  extends radially outward from the bearing  32  to attach at four points to the inner edge of the air passage  24 . The spider support  34  thus allows the passage of air around the outside of bearing  32  through the air passage  24 .  
         [0042]     Bearing  32  includes an axially extending keyway  35  which, in the preferred embodiment, has a cruciate cross-section.  
         [0043]     A circular valve disk  38  held within the volume  18  includes an axially extending key  40  having an outer cross section corresponding to the inner cross section of the keyway  35  so that the key  40  may move freely in an axial direction  36  but be restrained against rotation. The axially extending keyway  35  has a total cross sectional area that is small relative to the area of the circular valve disk  38  so that ice formed in the axially extending keyway  35  has reduced surface to which to adhere and may be more readily dislodged.  
         [0044]     The circular valve disk  38  lies in a plane perpendicular to the axial direction  36  and has an outer periphery including a radially extending and opening groove  44  that may receive an inner lip of an annular elastomeric washer  46 . The groove  44  thus holds the annular elastomeric washer  46  extending radially outward from the edge of the valve disk  38  in cantilevered fashion.  
         [0045]     Together the elastomeric washer  46  and the valve disk  38  comprise a damper plate  43  that may move axially to block air flow through the air passage  24  when the elastomeric washer  46  abuts a circular shoulder extending into the volume  18  and surrounding air passage  24  to form a damper seat  48 . When the damper plate  43  is displaced backward from damper seat  48 , air may flow freely around the damper plate  43  through the volume  18 .  
         [0046]     Attached concentrically within air passage  28  of rear housing portion  14  is a motor support  50 . The motor support is held centered within the air passage  28  on a spider support  52  (similar to spider support  34 ) supporting the motor support  50  and allowing air flow through air passage  28  and around the motor support  50 .  
         [0047]     Motor support  50  provides a shell into which a low-voltage, brush, DC permanent magnet motor  54  may fit with an axle  56  of the motor  54  extending forward along axial direction  36  into the volume  18 . Motor  54  may, for example, have an operating voltage of less than 12 volts and in the preferred embodiment an operating voltage of 1.5 volts and, a power consumption limited to less than a few watts.  
         [0048]     An axial threaded shaft  58  is press-fit to the axle  56  to be rotatable by the motor  54  and to extend through the volume  18 . The threaded shaft  58  is received by corresponding internal threads of the key  40  surrounding the threaded shaft like a collar. The threaded shaft  58  is of a length sufficient to extend into the keyway  35  after passing through the key  40 . Desirably, the key is always at least partially within the keyway to prevent the formation of capping ice that would block entry of the key  40  into the keyway  35 .  
         [0049]     In an alternative embodiment, the threads of the threaded shaft  58  may be received by an internally threaded ball joint that fits within the valve disk  38  and swivels to allow slight amounts of axial misalignment between valve disk  38  and the elastomeric washer  46  and damper seat  48 .  
         [0050]     Optionally, the exposed portion of the threaded shaft  58  may be covered by a rubber bellows (not shown) to provide resistance to ice build up.  
         [0051]     The motor  54  is held against axial movement within the motor support  50  by an end cap  60  which has hasps  62  engaging corresponding teeth (not shown) on the motor support  50  to retain the motor  54 . The outer circumference of the motor  54  is non-cylindrical and the motor support  50  conforms to that non-cylindrical shape to prevent rotation of the motor  54  within the motor support  50 .  
         [0052]     Helical compression springs  64  and  66  fit coaxially around the threaded shaft  58  on either side of the valve disk  38  (with helical compression spring  66  fitting over the key  40 ) so as to provide axial forces away from either rear housing portion  14  or front housing portion  16  as the valve disk  38  closely approaches the rear housing portion  14  or front housing portion  16 , respectively. The purpose of these helical springs is to prevent torque “lock” caused by an abrupt stopping of motion of the damper plate  43  as will be described below.  
         [0053]     Wires  70  may be attached to the motor  54  and include a series resistor  72  limiting motor stall current as will be described below. The series resistor  72  allows a voltage to be applied to the damper  10  in excess of the operating voltage of the motor  54 .  
         [0054]     The wires  70  pass out of the motor support  50  and end cap  60  to be received by a standard electrical connector  74  allowing simple attachment and removal of the electrical connections to the damper  10 .  
         [0055]     In use, the damper  10  may be operated to cause the motor  54  to move the damper plate  43  between an opened and closed state. As will be understood to those of ordinary skill in the art, electrical energy is required only during this period of movement and not during the time the damper  10  remains opened or closed after movement is complete.  
         [0056]     During operation to open the damper  10 , a control circuit (not shown) provides a reverse polarity electrical voltage to the motor  54  for a time period slightly longer than the time required for the motor  54  to fully retract the damper plate  43  from a closed state to an open position. At the open position, the damper plate  43  will be adjacent against a stop surface of the rear housing portion  14  compressing the compression spring  64  between the damper plate  43  and that stop surface.  
         [0057]     The length of the compression spring  64  is such as to engage (or alternatively to apply significant force to) both the damper plate  43  and a surface of the rear housing portion  14  only at the end of the travel of the damper plate  43 . As the damper plate  43  continues to open, the compression spring  64  slows the motor  54  reducing the rotational momentum of the motor  54  and threaded shaft  58  to below a predetermined amount before the damper plate  43  stops. This prevents the momentum from being converted into additional torque that might produce a frictional locking of the threads of the threaded shaft  58  and internal threads of the keyway  35  that cannot be overcome by later reversing the motor  54 .  
         [0058]     After that damper  10  is open, air may flow through the front housing portion  16  and out the rear housing portion  14  until a desired temperature relationship exists between two zones connected by the damper  10 . The desired temperature may be detected by a thermocouple or the like communicating with the control circuit driving the motor  54 .  
         [0059]     When the desired temperature range is reached, the control circuit may provide a positive polarity electrical voltage to the motor  54  for a time period slightly longer than the time required for the motor  54  to fully extend the damper plate  43  from the open state to the closed position abutting damper seat  48 . At this time, the compression spring  66  is compressed between a front portion of the valve disk  38  and a rear portion of the front housing portion  16 . Per the operation of the helical compression spring  64 , helical compression spring  66  resists the last increment of forward travel of the damper plate  43  slowing the motor  54  and threaded shaft  58  to prevent inertial locking of the threads of the threaded shaft  58  and internal threads of the keyway  35 .  
         [0060]     In an alternative embodiment, the slowing of the motor may be accomplished by flexure of the gasket or by inducted friction from a mechanism not subject to torque lock, for example, a friction pad applied to the axial threaded shaft  58 .  
         [0061]     At this point, the elastomeric washer  46  abuts the damper seat  48  and may flex inward slightly to bleed off additional rotational energy of the motor  54  and threaded shaft  58 . The damper plate  43  now closes air passage  24  preventing airflow through the housing  12 .  
         [0062]     In both opening and closing the damper  10 , the pulse of voltage provided to the motor  54  by the control circuit is longer than that required for full travel of the damper plate  43  thus ensuring complete opening and complete closing of the damper plate  43  without the need for feedback to the control circuit as might be otherwise provided by limit switches or other well known means. This open loop control of the motor  54  results in a stalling of the motor  54  when the damper plate  43  has reached the full extent of its travel in either direction. Additional current draw by the motor  54  at these times (until expiration of the current pulse) is limited by resistor  72  to prevent unacceptable heating of the motor  54  in a stall condition. A large proportion of voltage drop across the resistor  72  provides an essentially constant current to the motor  54  even during stall. The size of resistor  72  and the length of the stall period may be varied for particular applications and temperature ranges as will be understood by those with ordinary skill in the art.  
         [0063]     Direct drive of the valve disk  38  by a threaded shaft attached to motor  54  eliminates the need for a gear train or the like such as may be more expensive and subject to blockage by ice and the like. Unlike gear teeth, the threads of the threaded shaft  58  and internal threads on key  40  may be made self-cleaning. Ice within the keyway  35  is minimized by extending the threaded shaft  58  into the keyway  35 .  
         [0064]     In flapper-style dampers, adhesion between the flapper and damper opening away from the pivot point is made worse by the backward acting lever of the pivoting flapper. In the present design, an even speed and force of separation (and closure) is applied over the entire contacting region of the door and seat. The present design may also provide a quieter operation as there is no abrupt slapping of a door rapidly driven by a motor or solenoid.  
         [0065]     The elastomeric washer  46  may be constructed of a solid elastomeric material as opposed to a foam material, thus minimizing moisture retention and freezing problems. Foam gaskets, incorporating compressible open or closed air cells, are often required for high compliance gaskets needed in flapper type valves, where the different ends of the pivoting flapper experience different rates of closure and hence different compressions under a constant pivot torque and possibly different amounts of separation when closed as a result of manufacturing tolerances and variations in the balance between closure torque and gasket compression force. The air cells of these foam gaskets can hold moisture and often age poorly becoming brittle or fragile over time.  
         [0066]     Suitable compliance of the material of the elastomeric washer  46 , necessary to ensure an airtight sealing, is obtained from the cantilevered flexure of the elastomeric washer  46  rather than its compression as might require a foam material. Further, the even closing provided by the linear mechanism of the present invention requires far less gasket compliance than is required by flapper type designs.  
         [0067]     In an alternative embodiment, graduated opening of the damper  10  may be provided by replacing the motor  54  with a stepper motor of a type well known in the art. The position of the stepper motor and damper plate  43  may be determined by turning the stepper motor in one direction for an amount guaranteed to fully move the damper plate  43  across its full range of travel. Then a predetermined number of steps of the motor may be taken to move the damper plate  43  to a predetermined location between fully open and fully closed. The housing  12  inner surface may be tapered to promote a graduated control of air as a function of position of the valve disk  38  within the volume  18 .  
         [0068]     The threaded shaft  58  may be constructed of stainless steel material to resist corrosion in a moist and cold environment. The front housing portion  16 , rear housing portion  14 , and the valve disk  38  may be constructed of a self-lubricating plastic as may be readily injection molded.  
         [0069]     It will be recognized that the threaded shaft  58  may be used not only with disk-shaped valves or valves that translate linearly, but will accommodate other similar designs as would be understood by one of ordinary skill in the art.  
         [0070]     Application of the damper  10  may control refrigerator temperatures in different compartments of a refrigerator as well as other areas of airflow control including those associated with heating or the distribution of air in automobiles.  
         [0071]     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.