Abstract:
A fast engage, slow release electrical actuator combines an electromagnetic actuator with a thermal actuator, the latter which retains the electromagnetic actuator after the former has been actuated to delay the release thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     --  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     --  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates to electrical actuators useful in washing machines and the like, and in particular to an actuator that provides for rapid initial engagement with delayed release.  
         [0004]     Electrical actuators that rapidly engage upon receipt of an actuation signal, but that delay releasing when the actuation signal ceases may be used, for example, in a lid lock on a clothes washing machine. With such an actuator, the lid locks quickly upon the start of the spin cycle and remains locked for a period of time after the spin cycle ends to allow the spin basket to coast to a stop before the lid can be opened. Desirably, the electrical actuator should provide a slow release not only when the actuation signal ends, but in the event of unexpected power loss.  
         [0005]     Bi-metallic actuators, known in the art, can provide a slow release, either at the end of an actuation signal (heating the bi-metal) or upon power failure, as the bi-metal element cools. However, the same thermal mechanism that slows the cooling of the bi-metal also delays its heating undesirably delaying the engagement of the actuator.  
         [0006]     U.S. Pat. No. 5,823,017, assigned to the assignee of the present invention and hereby incorporated by reference, describes an electromagnetic actuator that may be actuated rapidly and which is bi-stable so as to retain actuation even in the absence of power. An associated timing circuit provides for a delayed release of the actuator upon cessation of the actuation signal. An energy storage capacitor allows operation of the timer circuit even in the absence of power.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The present invention provides an electrical actuator combining an electromagnetic actuator such as a solenoid, and a thermal actuator such as a wax motor to provide fast engagement and slow release. In a preferred embodiment, the wax motor is heated by the coil of the electromagnetic actuator allowing a single control signal to be used for the actuation. The use of a thermal actuator instead of a bi-stable electromagnetic actuator eliminates the need to store electrical energy for release in the event of power failure. A simple clip structure may be used to join the electromagnetic actuator and thermal actuator when their operators are co-axial and opposed, providing extremely inexpensive and simple mechanism.  
         [0008]     Specifically, the present invention provides a fast actuation, delayed release electrical actuator having an electromagnetic actuator responding to an initiation of an electrical current to move an operator from a first position to a second position, and a thermal actuator responding to a cessation of the electrical current to delay movement of the operator from the second position to the first position for a predetermined period after cessation of the electrical current.  
         [0009]     It is one object of at least one embodiment of the invention to provide a self-contained mechanism that provides fast actuation and delayed release without timer circuitry.  
         [0010]     The thermal actuator may be heated by current passing through a solenoid coil of the electromagnetic actuator. The heating of the thermal actuator may be inductive heating or conductive heating.  
         [0011]     It is thus another object of at least one embodiment of the invention to eliminate the need for a separate heater for the thermal actuator.  
         [0012]     The actuator may include a heating control reducing heating of the thermal actuator after the operator has moved from the first position to the second position.  
         [0013]     Thus it is another object of at least one embodiment of the invention to provide rapid heating of the thermal actuator while preventing overheating or excess power usage.  
         [0014]     The heater control may control current to the electromagnetic actuator, for example, by a switch that is actuated by movement of the operator or through a timer-controlled, current-controlled or heat sensitive switch.  
         [0015]     It is another object of at least one embodiment of the invention to provide a simple method of heat control by controlling current.  
         [0016]     The solenoid coil may have multiple windings, and the heating control may change the winding connections, for example, from parallel to serial or from two coils to one coil.  
         [0017]     Thus it is another object of at least one embodiment of the invention to provide current control without the need for complex circuitry.  
         [0018]     The multiple windings may be bifilar or may be spatially separated within the solenoid.  
         [0019]     Thus it is another object of at least one embodiment of the invention to allow for flexible control of the distribution of heating.  
         [0020]     The thermal actuator may be a wax motor and the electromagnetic actuator may include a solenoid coil wrapped around the wax motor.  
         [0021]     Thus is an object of at least one embodiment of the invention to provide a simple, compact design.  
         [0022]     A piston of the wax motor may extend along an axis of the solenoid coil in a first direction and the magnetically attractable actuator element of the electromagnetic actuator may be movable along the axis in a second direction, and the piston and actuator element may be joined by a rigid clip having a first end engaging a portion of the piston, and a second end engaging a portion of the actuator element to limit a maximum separation of the portions while allowing movement to lesser separations.  
         [0023]     Thus it is another object of at least one embodiment of the invention to provide a simple mechanism for combining a thermal and electromagnetic actuator.  
         [0024]     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  
       [0025]      FIG. 1  is an exploded, perspective view of an actuator according to a first embodiment of the present invention having a coaxial electromagnetic solenoid centered about a wax motor;  
         [0026]      FIG. 2  is an elevational cross-section through the assembled actuator of  FIG. 1  in a pre-actuation state with a solenoid plunger fully extended and a wax motor piston fully withdrawn;  
         [0027]      FIG. 3  is a figure similar to that of  FIG. 2  showing the actuator immediately after application of an actuation signal in an actuation state with the solenoid plunger fully withdrawn and the wax motor piston fully withdrawn;  
         [0028]      FIG. 4  is a figure similar to that of  FIGS. 2 and 3  showing the actuator after cessation of the actuation signal in a post-actuation state with the solenoid plunger fully retracted and the wax motor piston fully extended;  
         [0029]      FIG. 5  is a cross-sectional view similar to that of  FIG. 2  showing an alternative embodiment of the invention using a hinged armature instead of a plunger;  
         [0030]      FIG. 6  is a cross-sectional view of the solenoid coil of  FIGS. 1-4  showing a simple heating control circuit that allows control of the heating of the wax motor separately from the control of the magnetic force needed to attract the solenoid plunger;  
         [0031]      FIG. 7  is a fragmentary view of the bottom portion of the actuator of  FIG. 4  showing a switch that may be used to reduce the heating of the wax motor in the actuation state;  
         [0032]      FIG. 8  is a generalized schematic of a heating control that may use a switch activated by a timer, current sensor, or thermal element as would be understood in the art;  
         [0033]      FIG. 9  is a plot of current versus time showing three levels of current control for the different states of  FIGS. 2, 3  and  4 ; and  
         [0034]      FIG. 10  shows a control circuit for a bifilar winding that may connect the windings in series or parallel to control total current therethrough.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]     Referring to  FIG. 1 , an actuator  10  of the present invention provides generally a tubular form  12  about which a solenoid coil  14  may be wound. The tubular form  12  includes a central bore (not visible in  FIG. 1 ) which may receive a generally cylindrical ferromagnetic plunger  16  typically constructed of iron or steel. The plunger  16  may slide smoothly within the bore of the tubular form  12  as attracted by the solenoid coil  14  when the latter is energized.  
         [0036]     The solenoid coil  14 , as is understood in the art, is a coil of conductive wire and includes terminals or leads (not shown) for introducing a current into the solenoid coil to generate an axial magnetic field.  
         [0037]     The plunger  16  includes a reduced diameter inner end  20  that may engage the inside diameter of helical return spring  18 . The helical return spring  18 , in turn, has an outside diameter fitting freely within the bore of the tubular form  12 . In its relaxed state, the helical return spring  18  extends beyond the inner end  20  of the plunger  16  so that when the plunger  16  and helical return spring  18  are inserted into the bore of the tubular form  12 , the outer end of the helical return spring  18  engages structure within the bore of the tubular form  12 , such as a shelf or an end of a wax motor (described below) so that the helical return spring  18  provides an outward return force to the plunger  16  after the plunger  16  is attracted into the solenoid coil  14  and then released.  
         [0038]     The outer end of the plunger  16  includes an extension arm  22  also of reduced diameter with respect to the plunger  16  to provide a shoulder  24  at the outer end of the plunger  16 . The outer end of the extension arm  22  includes a head  26  to engage a device (not shown) intended to be actuated by the actuator  10 .  
         [0039]     A cylindrical wax motor  28  is located in the bore of the tubular form  12  at an end opposite that end of the bore receiving the plunger  16 . The wax motor  28  has a piston  30  extending outward from the solenoid coil  14  along the axis of the bore of the tubular form  12  in the opposite direction from the plunger  16 . As is understood in the art, the wax motor  28  contains a thermally expanding material such as wax which, when heated, expels the piston  30 . The wax motor  28  may be attached to the tubular form  12  by a press fit or may be simply blocked from upward motion by a shelf or the like within the bore of the tubular form  12 .  
         [0040]     Continuing to refer to  FIG. 1 , the tubular form  12  has stilt plates  32  extending perpendicularly to the axis of the bore of the tubular form  12  abutting each end of the solenoid coil  14 . The stilt plate  32  at the end of the tubular form  12  surrounding the plunger  16  provides an opening through which an upper end of the tubular form  12  may pass and extend a distance through the stilt plate  32  away from the solenoid coil  14 . The stilt plate  32  at the end of the tubular form  12  surrounding the wax motor  28  provides an opening allowing an end of the wax motor  28  and piston  30  to extend therethrough. Projections extending from the stilt plates  32  allow the tubular form  12  to be attached to the stationary structure to provide an anchor point for the actuator  10 .  
         [0041]     The plunger  16  extends out of one end of the tubular form  12  and the piston  30  of the wax motor  28  extends out of the other end of the tubular form  12 . The outward, opposite projections of the plunger  16  and piston  30  are contained by a bridle element  34  consisting of a U-band  36  having a base  40  between two axially extending legs  38 . The base  40  has a bore  42  sized to pass the head  26  of the plunger  16 , but to block shoulder  24  of the plunger thereby restraining outward movement of the plunger  16 .  
         [0042]     The legs  38  of the bridle element  34  extend on either side of the solenoid coil  14  to an opposite end of the tubular form  12  near the wax motor  28 . The free ends of the legs  38  are joined by a spanner  44  having teeth  46  press fit into corresponding sockets  48  in the ends of the legs  38  to retain these parts together once they are assembled. The spanner  44  includes an upwardly extending cup  50  that may receive the lower end of the wax motor  28  when the piston  30  is retracted so that the cup  50  abuts one stilt plate  32 .  
         [0043]     Generally, the legs  38  are retained within notches  52  in the edges of the stilt plates  32  to slide freely with respect to the stilt members  23  parallel to an axis of the bore of the tubular form  12  and hence parallel to movement of the plunger  16  and piston  30  of the wax motor  28 . The bridle element  34  including spanner  44 , cup  50 , and U-band may be ferromagnetic so as to provide for a flux path assisting in retraction of the plunger  16  when the solenoid coil  14  is energized as will be described.  
         [0044]     A helical compression spring  56  fits between the base  40  of the bridle element  34  and one stilt plate  32  as retained around an extending end of the tubular form  12 . The helical compression spring  56  serves to bias the bridle element  34  outward compressing the piston  30  of the wax motor  28  inward. In the position of maximum outward bias, the base  40  of the bridle element  34  allows full extension of the plunger  16  while the cup  50  of the bridle element  34  abuts its associated stilt plate  32 .  
         [0045]     Referring now to  FIG. 2 , when the actuator  10  is in a pre-actuation state, the plunger  16  is biased upward by the spring  18  (not shown in  FIG. 2  for clarity) so that the head  26  of the plunger  16  is in a full extension position. The solenoid coil  14  is de-energized and the wax motor  28  is cool so that its piston  30  is fully retracted allowing the bridle element  34  to be biased to its full upward position by spring  56  (also not shown in  FIG. 2  for clarity). The shoulder  24  of the plunger  16  is restrained from further outward motion by the base  40  of the bridle element  34 .  
         [0046]     Referring now to  FIG. 3  when the actuator  10  is in an actuation state, the plunger  16  (also simplified for clarity) is pulled into the tubular form  12 , drawing the head  26  to its fully retracted position. The shoulder  24  of the plunger  16  is pulled away from the base  40  of the bridle element  34 , the latter which is held outward by the spring  56  shown in  FIG. 1 . This magnetic field produced by current passing through the solenoid coil  14  is conducted in part by the metallic parts of the bridle element  34  improving this force of attraction.  
         [0047]     Referring now to  FIG. 4 , when the actuator  10  is in a post-actuation state, after a period of actuation of the solenoid coil  14  during which the wax motor  28  becomes heated, the piston  30  is forced outward from the casing of the wax motor  28 , pushing outward on the spanner  44  of the bridle element  34  whose base  40  moves inward to again engage the shoulder  24  of the plunger  16 . While the present inventors do not wish to be bound by a particular theory, it is believed that the heating is both a result of the conduction of heat from the windings of the solenoid coil  14  whose temperature rises from resistive heating, and a result of inductively induced eddy currents in the components of the wax motor  28  itself.  
         [0048]     It will be understood that in the post-actuation state, a loss of power to the solenoid coil  14  resulting either from a disabling of the actuator  10  by turning off the solenoid coil  14  or a loss of power to the system holding the actuator  10  will not cause an immediate release or extension of the plunger  16  which, although no longer held by the magnetic attraction of the solenoid coil  14 , is held retracted by the bridle element  34  as biased by the wax motor  28 .  
         [0049]     This state persists until the wax motor  28  cools to allow retraction of the piston  30  under the force of the helical spring  56  (shown in  FIG. 1 ) acting on the bridle element  34 . The speed of this cooling process may be controlled to be much longer than the release of the plunger  16  by the solenoid coil  14  when power is cut from the solenoid coil  14 .  
         [0050]     In this way, the plunger  16  may be rapidly actuated to move inward, but after a predetermined actuation time such as heats the wax motor  28 , the plunger  16  will extend slowly as dictated by the cooling of the wax motor  28 . The relative speed of heating of the wax motor  28  may generally be set to be much faster than the speed of cooling of the wax motor  28  by control of the heating power and thermal resistance between the wax motor  28  and the environment.  
         [0051]     After cooling of the wax motor  28 , the actuator  10  returns to the de-energized state shown in  FIG. 2 .  
         [0052]     Referring now to  FIG. 5 , it will be understood that this same principle described above may be applied to an electrical “relay-style” design. In this embodiment, the wax motor  28  provides a core for the solenoid coil  14  with the height of the solenoid coil  14  being substantially the same as the length of the wax motor  28 . A ferromagnetic frame  62  is attached to the solenoid coil  14  and supports a hinged armature  60  that, in a released position, may swing outward away from the core formed by wax motor  28  and in an engaged position, when the solenoid coil  14  is energized, may swing inward toward the core formed by wax motor  28 . The armature may be optionally associated with electrical contacts (not shown) as will be understood to those of ordinary skill in the art.  
         [0053]     The frame  62  includes an opening  64  in a face of the frame  62  supporting the side of the solenoid coil  14  away from the armature  60  allowing downward passage of the piston  30 . The piston  30  may in turn engage a bridle element  34  also engaging the outer surface of the armature  60 .  
         [0054]     When the armature  60  is attracted inward by energizing the solenoid coil  14 , it moves quickly under the influence of the electromagnetic field. With heating of the wax motor  28  by the solenoid coil  14 , the piston  30  extends from the wax motor  28  causing the bridle element  34  to hold the armature  60  inward independently of its magnetic attraction. Again, release of the armature  60  is delayed by the time required to cool the wax motor  28 . For clarity, a spring for biasing the armature  60  and for biasing the bridle element  34  are not shown in  FIG. 5 . The position and function of these springs will be understood to one of ordinary skill in the art from the above description.  
         [0055]     Referring now to  FIG. 6 , in one embodiment, the solenoid coil  14  may be wound in two parts, a first coil portion  14   a  around one end of the tubular form  12  surrounding the plunger  16 , and second coil portion  14   b  around the opposite end of the tubular form  12  surrounding the wax motor  28 . During the actuation state of  FIG. 2  above, a voltage  66  may be connected through a switch  68  (for example, as part of an appliance cycle timer) to the first coil portion  14   a  and through a heating control  70  to the second coil portion  14   b.    
         [0056]     Once the wax motor  28  is fully heated, the heating control  70  may stop the current through second coil portion  14   b , for example, by opening a switch, or decrease the current through the second coil portion  14   b , for example, by connecting a rectifier in series with the second coil portion to reduce the heating of wax motor  28  while ensuring the piston  30  remains fully extended and the plunger fully retracted. The heating control  70  may be a switch connected to a time delay, a thermostat, a current sensor, or the like.  
         [0057]     Referring now to  FIG. 7 , heating control  70  may alternatively be a mechanical switch  72  operated by movement of the actuator  10 . The switch may have opposed contacts  74  in series with the second coil portion  14   b , one contact  74  mounted on a leaf spring  76  engaging with the bottom of the spanner  44  so that the contacts  74  are opened when the wax motor piston  30  is fully extended.  
         [0058]     Referring now to  FIG. 8  alternatively, the heating control  70  may control the current to the entire singly wound solenoid coil  14 , for example, using current control circuitry known in the art, for example, SCR or resistive current control.  
         [0059]     Referring to  FIG. 9 , the heating control  70  of  FIGS. 6 and 8  may, in one embodiment, control the current through the solenoid coil  14  according to a sub-state of the actuator  10 . In a first sub-state  78  of the actuation state of  FIG. 2 , a large current is provided to the solenoid coil  14  to provide the strongest force of magnetic attraction of the plunger  16  and the most rapid heating of the wax motor  28 . At a second sub-state  80  of the actuation state of  FIG. 2 , a lower current is provided commensurate with the lower forces required to retain the plunger  16  in the retracted position while still providing heating of the wax motor  28 . In a third sub-state  82 , the current is further reduced to that required to hold the plunger in place and reduce heating of the wax motor to a steady state heat requirement.  
         [0060]     Referring now to  FIG. 10 , in an alternative embodiment, solenoid coil  14  may be wound in bifilar fashion to provide co-extensive first coil portion  14   a  and second coil portion  14   b . A switch circuit  84  which may be a mechanical or solid state switch may be operated in a first mode in which the switch throws are moved downward to provide for a parallel connection of the first coil portion  14   a  and second coil portion  14   b , and hence relatively greater current flow and heating, and a second position shown in  FIG. 10  in which the switch throws are moved upward providing for a series connection of the first coil portion  14   a  and second coil portion  14   b , and relatively lesser current flow and heating.  
         [0061]     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.