Linear travel air damper

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.

BACKGROUND OF THE INVENTION

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.

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.

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.

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.

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.

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

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.

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.

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.

The motor may be a permanent magnet DC brush motor having an operating voltage of less than 12 volts.

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.

The damper may include a gasket formed from a material without air cells as part of the damper plate and/or damper seat.

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.

The gasket may be an elastomeric material cantilevered in radial extension at the periphery of the damper plate.

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.

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.

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.

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.

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.

The keyway may be open at two axial ends so that movement of the collar through the keyway may eject accumulated ice.

Thus, it is another object of at least one embodiment of the invention to prevent ice from being compacted within the keyway.

The collar may be positioned at least partially within the keyway at extreme positions of the collar.

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.

The housing and damper plate may be thermoplastic material.

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.

The lead screw may be stainless steel.

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.

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.

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.

The spring may be a helical compression spring fitting coaxially about the axial drive shaft between the stop and the damper plate.

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.

The motor may include a series, current-limiting resistor allowing the motor to operate in stall condition without damage.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIGS. 1 and 2, the damper10of the present invention may provide a generally rectangular housing12having a rear housing portion14and a front housing portion16fitting together to enclose a volume18through which air may flow in a generally axial direction36. The front housing portion16and rear housing portion14are held together by means of laterally extending teeth20on the sides of the front housing portion16that are engaged by corresponding axially extending hasps22on the sides of rear housing portion14or by welding or other similar method.

In use, the housing12blocks an opening between two compartments between which airflow must be controlled, for example, in a refrigerator. Front housing portion16provides a generally circular air passage24on its front rectangular face26whereas rear housing portion14includes a generally rectangular air passage28on its rear rectangular face30. In the preferred embodiment, each air passage24may be approximately 3 square inches in area.

Supported coaxially within air passage24is a front bearing32held by a spider support34. The spider support34extends radially outward from the bearing32to attach at four points to the inner edge of the air passage24. The spider support34thus allows the passage of air around the outside of bearing32through the air passage24.

Bearing32includes an axially extending keyway35which, in the preferred embodiment, has a cruciate cross-section.

A circular valve disk38held within the volume18includes an axially extending key40having an outer cross section corresponding to the inner cross section of the keyway35so that the key40may move freely in an axial direction36but be restrained against rotation. The axially extending keyway35has a total cross sectional area that is small relative to the area of the circular valve disk38so that ice formed in the axially extending keyway35has reduced surface to which to adhere and may be more readily dislodged.

The circular valve disk38lies in a plane perpendicular to the axial direction36and has an outer periphery including a radially extending and opening groove44that may receive an inner lip of an annular elastomeric washer46. The groove44thus holds the annular elastomeric washer46extending radially outward from the edge of the valve disk38in cantilevered fashion.

Together the elastomeric washer46and the valve disk38comprise a damper plate43that may move axially to block air flow through the air passage24when the elastomeric washer46abuts a circular shoulder extending into the volume18and surrounding air passage24to form a damper seat48. When the damper plate43is displaced backward from damper seat48, air may flow freely around the damper plate43through the volume18.

Attached concentrically within air passage28of rear housing portion14is a motor support50. The motor support is held centered within the air passage28on a spider support52(similar to spider support34) supporting the motor support50and allowing air flow through air passage28and around the motor support50.

Motor support50provides a shell into which a low-voltage, brush, DC permanent magnet motor54may fit with an axle56of the motor54extending forward along axial direction36into the volume18. Motor54may, 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.

An axial threaded shaft58is press-fit to the axle56to be rotatable by the motor54and to extend through the volume18. The threaded shaft58is received by corresponding internal threads of the key40surrounding the threaded shaft like a collar. The threaded shaft58is of a length sufficient to extend into the keyway35after passing through the key40. Desirably, the key is always at least partially within the keyway to prevent the formation of capping ice that would block entry of the key40into the keyway35.

In an alternative embodiment, the threads of the threaded shaft58may be received by an internally threaded ball joint that fits within the valve disk38and swivels to allow slight amounts of axial misalignment between valve disk38and the elastomeric washer46and damper seat48.

Optionally, the exposed portion of the threaded shaft58may be covered by a rubber bellows (not shown) to provide resistance to ice build up.

The motor54is held against axial movement within the motor support50by an end cap60which has hasps62engaging corresponding teeth (not shown) on the motor support50to retain the motor54. The outer circumference of the motor54is non-cylindrical and the motor support50conforms to that non-cylindrical shape to prevent rotation of the motor54within the motor support50.

Helical compression springs64and66fit coaxially around the threaded shaft58on either side of the valve disk38(with helical compression spring66fitting over the key40) so as to provide axial forces away from either rear housing portion14or front housing portion16as the valve disk38closely approaches the rear housing portion14or front housing portion16, respectively. The purpose of these helical springs is to prevent torque “lock” caused by an abrupt stopping of motion of the damper plate43as will be described below.

Wires70may be attached to the motor54and include a series resistor72limiting motor stall current as will be described below. The series resistor72allows a voltage to be applied to the damper10in excess of the operating voltage of the motor54.

The wires70pass out of the motor support50and end cap60to be received by a standard electrical connector74allowing simple attachment and removal of the electrical connections to the damper10.

In use, the damper10may be operated to cause the motor54to move the damper plate43between 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 damper10remains opened or closed after movement is complete.

During operation to open the damper10, a control circuit (not shown) provides a reverse polarity electrical voltage to the motor54for a time period slightly longer than the time required for the motor54to fully retract the damper plate43from a closed state to an open position. At the open position, the damper plate43will be adjacent against a stop surface of the rear housing portion14compressing the compression spring64between the damper plate43and that stop surface.

The length of the compression spring64is such as to engage (or alternatively to apply significant force to) both the damper plate43and a surface of the rear housing portion14only at the end of the travel of the damper plate43. As the damper plate43continues to open, the compression spring64slows the motor54reducing the rotational momentum of the motor54and threaded shaft58to below a predetermined amount before the damper plate43stops. This prevents the momentum from being converted into additional torque that might produce a frictional locking of the threads of the threaded shaft58and internal threads of the keyway35that cannot be overcome by later reversing the motor54.

After that damper10is open, air may flow through the front housing portion16and out the rear housing portion14until a desired temperature relationship exists between two zones connected by the damper10. The desired temperature may be detected by a thermocouple or the like communicating with the control circuit driving the motor54.

When the desired temperature range is reached, the control circuit may provide a positive polarity electrical voltage to the motor54for a time period slightly longer than the time required for the motor54to fully extend the damper plate43from the open state to the closed position abutting damper seat48. At this time, the compression spring66is compressed between a front portion of the valve disk38and a rear portion of the front housing portion16. Per the operation of the helical compression spring64, helical compression spring66resists the last increment of forward travel of the damper plate43slowing the motor54and threaded shaft58to prevent inertial locking of the threads of the threaded shaft58and internal threads of the keyway35.

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 shaft58.

At this point, the elastomeric washer46abuts the damper seat48and may flex inward slightly to bleed off additional rotational energy of the motor54and threaded shaft58. The damper plate43now closes air passage24preventing airflow through the housing12.

In both opening and closing the damper10, the pulse of voltage provided to the motor54by the control circuit is longer than that required for full travel of the damper plate43thus ensuring complete opening and complete closing of the damper plate43without 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 motor54results in a stalling of the motor54when the damper plate43has reached the full extent of its travel in either direction. Additional current draw by the motor54at these times (until expiration of the current pulse) is limited by resistor72to prevent unacceptable heating of the motor54in a stall condition. A large proportion of voltage drop across the resistor72provides an essentially constant current to the motor54even during stall. The size of resistor72and 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.

Direct drive of the valve disk38by a threaded shaft attached to motor54eliminates 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 shaft58and internal threads on key40may be made self-cleaning. Ice within the keyway35is minimized by extending the threaded shaft58into the keyway35.

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.

The elastomeric washer46may 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.

Suitable compliance of the material of the elastomeric washer46, necessary to ensure an airtight sealing, is obtained from the cantilevered flexure of the elastomeric washer46rather 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.

In an alternative embodiment, graduated opening of the damper10may be provided by replacing the motor54with a stepper motor of a type well known in the art. The position of the stepper motor and damper plate43may be determined by turning the stepper motor in one direction for an amount guaranteed to fully move the damper plate43across its full range of travel. Then a predetermined number of steps of the motor may be taken to move the damper plate43to a predetermined location between fully open and fully closed. The housing12inner surface may be tapered to promote a graduated control of air as a function of position of the valve disk38within the volume18.

The threaded shaft58may be constructed of stainless steel material to resist corrosion in a moist and cold environment. The front housing portion16, rear housing portion14, and the valve disk38may be constructed of a self-lubricating plastic as may be readily injection molded.

It will be recognized that the threaded shaft58may 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.

Application of the damper10may 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.