Patent Publication Number: US-2015059200-A1

Title: Dryer appliance and a method for operating the same

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to dryer appliances and methods for operating dryer appliances. 
     BACKGROUND OF THE INVENTION 
     Certain dryer appliances include a cabinet with a drum rotatably mounted therein. A heating assembly, such as an electric resistance heating element or a gas burner, can supply heated air to a chamber of the drum. For example, certain dryer appliances include a duct mounted to a back wall of the drum. The duct can direct heated air from the heating assembly into the chamber of the drum during operation of the dryer appliance. The duct generally includes an inlet that receives heated air from the heating assembly and a plurality of outlets for directing such heated air into the chamber of the drum. Such heated air can assist with drying articles located within the drum&#39;s chamber. 
     Heated air exiting the duct&#39;s outlets is preferably maintained below a certain threshold temperature, e.g., to avoid damaging articles that are drying within the chamber of the drum and other overheating problems. Certain dryer appliances are equipped with temperature sensors for monitoring the temperature of heated air entering the drum&#39;s chamber. If the temperature sensor detects overly hot air entering the drum&#39;s chamber, the heating assembly can be deactivated or cycled. 
     To further assist with regulating operation of the heating assembly, certain dryer appliances include a thermostat mounted to the heating assembly. The thermostat is configured for cycling at a threshold temperature. When the thermostat cycles, the heating assembly can be deactivated. Thermostats generally have an expected lifetime defined by a number of cycles the thermostats can be expected to perform. Thus, cycling of the thermostat is preferably limited to avoid approaching the expected lifetime of the thermostat. However, certain dryer conditions can cause the thermostat to trip frequently, such as when dryer appliances are operating in a restricted condition. 
     Accordingly, a dryer appliance with features for limiting cycling of a thermostat of the dryer appliance would be useful. In particular, a dryer appliance with features for limiting cycling of a thermostat of the dryer appliance when the dryer appliance is operating in a restricted condition would be useful. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present subject matter provides a dryer appliance and a method for operating a dryer appliance. The method includes monitoring a first temperature sensor of the dryer appliance in order to determine a number of cycles of the first temperature sensor. If the number of cycles of the heating element exceeds a threshold number, a temperature set point of a second temperature sensor of the dryer appliance is reduced. The method can assist with reducing or avoiding excessive cycling of the first temperature sensor. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention. 
     In a first exemplary embodiment, a method for operating a dryer appliance is provided. The method includes operating the dryer appliance in order to dry articles within a drum of the dryer appliance, monitoring a first temperature sensor of the dryer appliance in order to determine a number of cycles of the first temperature sensor during the step of operating, reducing a temperature set point of a second temperature sensor of the dryer appliance if the number of cycles of the first temperature sensor exceeds a threshold number during the step of monitoring. 
     In a second exemplary embodiment, a dryer appliance is provided. The dryer appliance includes a cabinet and a drum rotatably mounted within the cabinet. The drum defines a chamber for receipt of articles for drying. A motor is configured for selectively rotating the drum within the cabinet. A heating assembly is configured for directing a flow of heated fluid into the chamber of the drum. The heating assembly includes a housing, a heating element disposed within the housing, and a duct extending between the housing and the drum. The duct has an outlet positioned at the chamber of the drum. A first temperature sensor is positioned at the housing. A second temperature sensor is positioned at the outlet of the duct. A controller is in communication with the motor, the heating element and the first and second temperature sensors. The controller is configured for setting a temperature set point of the second temperature sensor to a first temperature set point, determining if an operating condition of the dryer appliance is a restricted condition, adjusting the temperature set point of the second temperature sensor to a second temperature set point if the operating condition is the restricted condition at the step of determining, monitoring the first temperature sensor in order to determine a number of cycles of the first temperature sensor, and changing the temperature set point of the second temperature sensor to a third temperature set point if the number of cycles of the first temperature sensor exceeds a threshold number during the step of monitoring. 
     In a third exemplary embodiment, a method for operating a dryer appliance is provided. The method includes setting a temperature set point of a thermistor of the dryer appliance to a first temperature set point, determining if an operating condition of the dryer appliance is a restricted condition, adjusting the temperature set point of the thermistor to a second temperature set point if the operating condition is the restricted condition at the step of determining, monitoring a thermostat of the dryer appliance in order to determine a number of cycles of the thermostat, and changing the temperature set point of the thermistor to a third temperature set point if the number of cycles of the thermostat exceeds a threshold number during the step of monitoring. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures. 
         FIG. 1  provides a perspective view of a dryer appliance according to an exemplary embodiment of the present subject matter. 
         FIG. 2  provides a perspective view of the exemplary dryer appliance of  FIG. 1  with portions of a cabinet of the exemplary dryer appliance removed to reveal certain components of the exemplary dryer appliance. 
         FIG. 3  provides a schematic view of certain components of the exemplary dryer appliance of  FIG. 1 . 
         FIG. 4  illustrates a method for operating a dryer appliance according to an exemplary embodiment of the present subject matter. 
         FIG. 5  illustrates a method for operating a dryer appliance according to an additional exemplary embodiment of the present subject matter. 
         FIGS. 6 and 7  illustrate plots of time versus exemplary temperature measurements of a temperature sensor. 
     
    
    
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG. 1  illustrates a dryer appliance  10  according to an exemplary embodiment of the present subject matter.  FIG. 2  provides another perspective view of dryer appliance  10  with a portion of a cabinet or housing  12  of dryer appliance  10  removed in order to show certain components of dryer appliance  10 . While described in the context of a specific embodiment of dryer appliance  10 , using the teachings disclosed herein it will be understood that dryer appliance  10  is provided by way of example only. Other dryer appliances having different appearances and different features may also be utilized with the present subject matter as well. Dryer appliance  10  defines a vertical direction V, a lateral direction L, and a transverse direction T. The vertical direction V, lateral direction L, and transverse direction T are mutually perpendicular and form and orthogonal direction system. 
     Cabinet  12  includes a front panel  14 , a rear panel  16 , a pair of side panels  18  and  20  spaced apart from each other by front and rear panels  14  and  16 , a bottom panel  22 , and a top cover  24 . Within cabinet  12  is a drum or container  26  mounted for rotation about a substantially horizontal axis, e.g., that is parallel or substantially parallel to the lateral direction L. Drum  26  defines a chamber  25  for receipt of articles, e.g., clothing, linen, etc., for drying. Drum  26  extends between a front portion  37  and a back portion  38 , e.g., along the lateral direction L. 
     A motor  31  is configured for rotating drum  26  about the horizontal axis, e.g., via a pulley and a belt (not shown). Drum  26  is generally cylindrical in shape, having an outer cylindrical wall or cylinder  28  and a front flange or wall  30  that defines an entry  32  of drum  26 , e.g., at front portion  37  of drum  26 , for loading and unloading of articles into and out of chamber  25  of drum  26 . A plurality of tumbling ribs  27  are provided within chamber  25  of drum  26  to lift articles therein and then allow such articles to tumble back to a bottom of drum  26  as drum  26  rotates. Drum  26  also includes a back or rear wall  34 , e.g., at back portion  38  of drum  26 . Cylinder  28  is rotatable on rear wall  34  as will be understood by those skilled in the art. 
     A duct  41  is mounted to rear wall  34  and receives heated air that has been heated by a heating assembly or system  40 . Duct  41  extends between heating assembly  40  and drum  26 . Duct  41  is configured for directing a flow of heated from heating assembly  40  into chamber  25  of drum  26  and has an outlet  82  positioned at chamber  25  of drum  26 . Heated air flows out of duct  41  into chamber  25  of drum  25  at outlet  82 . 
     Motor  31  is also in mechanical communication with an air handler  48  such that motor  31  rotates a fan  49 , e.g., a centrifugal fan, of air handler  48 . Air handler  48  is configured for drawing air through chamber  25  of drum  26 , e.g., in order to dry articles located therein as discussed in greater detail below. In alternative exemplary embodiments, dryer appliance  10  may include an additional motor (not shown) for rotating fan  49  of air handler  48  independently of drum  26 . 
     Drum  26  is configured to receive heated air that has been heated by a heating assembly  40 , e.g., in order to dry damp articles disposed within chamber  25  of drum  26 . Heating assembly  40  includes a heating element  42  ( FIG. 3 ), such as a gas burner or an electrical resistance heating element, for heating air. Heating element  42  is positioned within a housing  44  of heating assembly  40  in cabinet  12 . As discussed above, during operation of dryer appliance  10 , motor  31  rotates drum  26  and fan  49  of air handler  48  such that air handler  48  draws air through chamber  25  of drum  26  when motor  31  rotates fan  49 . In particular, ambient air enters heating assembly  40  via an entrance  51  due to air handler  48  urging such ambient air into entrance  51 . Such ambient air is heated within heating assembly  40  by heating element  42  and exits heating assembly  40  as heated air. Air handler  48  draws such heated air through duct  41  to drum  26 . The heated air enters drum  26  at outlet  82  of duct  41  positioned at rear wall  34  of drum  26 . 
     Within chamber  25 , the heated air can accumulate moisture, e.g., from damp articles disposed within chamber  25 . In turn, air handler  48  draws moisture statured air through a screen filter (not shown) which traps lint particles. Such moisture statured air then enters an exit conduit  46  and is passed through air handler  48  to an exhaust conduit  52 . From exhaust conduit  52 , such moisture statured air passes out of dryer appliance  10  through a vent  53  defined by cabinet  12 . After the clothing articles have been dried, they are removed from the drum  26  via entry  32 . A door  33  provides for closing or accessing drum  26  through entry  32 . 
     A cycle selector knob  70  is mounted on a cabinet backsplash  71  and is in communication with a processing device or controller  56 . Signals generated in controller  56  operate motor  31  and heating assembly  40  in response to the position of selector knobs  70 . Alternatively, a touch screen type interface, knobs, sliders, buttons, speech recognition, etc., mounted to cabinet backsplash  71  can permit a user to input control commands for dryer appliance  10  and/or controller  56 . 
     Controller  56  may include memory and one or more processing devices such as microprocessors, CPUs or the like, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with operation of dryer appliance  10 . The memory can represent random access memory such as DRAM, or read only memory such as ROM or FLASH. The processor executes programming instructions stored in the memory. The memory may be a separate component from the processor or may be included onboard within the processor. Alternatively, controller  56  may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software. 
       FIG. 3  provides a schematic view of certain components of dryer appliance  10 . As may be seen in  FIG. 3 , controller  56  is in operative communication with various components of dryer appliance  10 . In particular, controller  56  is in operative communication with motor  31  and heating assembly  40 . Thus, upon receiving an activation signal from cycle selector knob  70 , controller  56  can activate motor  31  to rotate drum  26  and fan  49  of air handler  48 . Controller  56  can also activate heating assembly  40  in order to generate heated air for drum  26 , e.g., in the manner described above. 
     Controller  56  is also in communication with a first temperature sensor  90  and a second temperature sensor  92 . First temperature sensor  90  is positioned at or adjacent heating assembly  40 , e.g., on housing  44  of heating assembly  40 . Thus, first temperature sensor  90  may be configured for measuring or detecting a temperature of housing  44  of heating assembly  40  or heated air within housing  44  of heating assembly  40 . In response to the temperature of housing  44  measured by first temperature sensor  90  exceeding a maximum permitted temperature, heating assembly  40  or any other component of dryer appliance  10  can be deactivated in order to reduce the temperature of heated air within heating assembly  40  and duct  41 . First temperature sensor  90  can be any suitable sensor. For example, first temperature sensor  90  may be a thermostat, such as a bimetallic switch. 
     Second temperature sensor  92  is configured for measuring a temperature of heated air within duct  41 . Second temperature sensor  92  can be positioned at any suitable location within dryer appliance  10 . For example, second temperature sensor  92  may be positioned within or on duct  41 , such as at outlet  82  of duct  41 . Controller  56  can receive a signal from second temperature sensor  92  that corresponds to a temperature measurement of heated air within duct  41 , e.g., a temperature measurement of heated air exiting duct  41  at outlet  82 . Second temperature sensor  92  can be any suitable sensor. For example, second temperature sensor  92  may be a thermistor or a thermocouple. 
     Dryer appliance  10  also includes features for improving performance of dryer appliance  10 . In particular, dryer appliance  10  includes features for limiting cycling of first temperature sensor  90  of dryer appliance  10 . Such features are discussed in greater detail below. 
     As will be understood by those skilled in the art, dryer appliance  10  can be installed at various locations. The particular arrangement and setup of dryer appliance  10  at such locations can affect performance of dryer appliance  10 . For example, a conduit (not shown) can be attached to vent  53  ( FIG. 2 ) of dryer appliance  10  and receive moisture saturated air therefrom. The conduit can direct such moisture statured air out of a building housing dryer appliance  10 . Thus, the conduit assists dryer appliance  10  with drying articles. However, the length of conduit can affect performance of dryer appliance  10 . For example, if the conduit is relatively long, it can be more difficult for air handler  48  to urge air out of vent  53  and through the conduit. Conversely, it can be relatively easier for air handler  48  to urge air out of vent  53  and through the conduit if the conduit is relatively short. The length of the conduit can vary depending upon the location of dryer appliance  10  within building. Thus, if dryer appliance  10  is located near an exterior wall, the conduit can be relatively short. Conversely, the conduit can be relatively long if dryer appliance  10  is distant from the exterior wall. 
     In a similar manner, lint and other debris within the conduit can also affect performance of dryer appliance  10 . For example, if the conduit has a relatively large volume of debris therein, it can be more difficult for air handler  48  to urge air out of vent  53  and through the conduit. Conversely, it can be relatively easier for air handler  48  to urge air out of vent  53  and through the conduit if the conduit has a relatively small volume of debris therein. 
     Accordingly, the length of the conduit, the volume of debris within the conduit, and other factors can affect performance of dryer appliance  10 . When such factors negatively affect performance of dryer appliance  10  to a significant degree, dryer appliance  10  is operating in a restricted condition. Conversely, dryer appliance  10  is operating in an unrestricted condition when such factors do not affect performance of dryer appliance  10  to a significant degree. As an example, when the conduit is relatively long and/or the conduit contains a relatively large volume of debris, dryer appliance  10  is operating in the restricted condition. Conversely, dryer appliance  10  is operating in the unrestricted condition when the conduit is relatively short and/or the conduit contains a relatively small volume of debris. 
     In the unrestricted condition, a volume of heated air flowing out of duct  41  can be relatively high, and a temperature of the heated air can be relatively low. Conversely, in the restricted condition, the volume of heated air flowing out of duct  41  can be relatively low, and the temperature of the heated air flowing out of duct  41  can be relatively high. Due to the increased temperature of heated air in duct  41  and housing  44  of heating assembly in the restricted condition, first temperature sensor  90  can trip or cycle and deactivate heating assembly  40 . First temperature sensor  90  has an expected life time defined by a number of trips or cycles performed by first temperature sensor  90 . Dryer appliance  10  includes features for limiting or reducing cycling of first temperature sensor  90  in order to preserve first temperature sensor  90 . In particular, dryer appliance  10  includes features for avoiding unnecessary or excessive cycling of first temperature sensor  90  when dryer appliance  10  is operating in the restricted condition. 
       FIG. 4  illustrates a method  400  for operating a dryer appliance according to an exemplary embodiment of the present subject matter. Method  400  can be used to operate any suitable dryer appliance. For example, method  400  may be used to operate dryer appliance  10  ( FIG. 1 ). In particular, controller  56  ( FIG. 3 ) may be programmed to implement method  400 . 
     At step  410 , dryer appliance  10  is operated in order to dry articles within drum  26 . As an example, a user can utilize knobs  70  to activate dryer appliance  10 . In response to the user actuating knobs  70 , controller  56  can operate motor  31  to spin drum  26  and fan  49  of air handler  48  at step  410 . Controller  56  can also activate heating element  42  of heating assembly  40  to supply heated air to chamber  25  of drum  26  at step  410 . 
     At step  420 , first temperature sensor  90  is monitored in order to determine a number of cycles of first temperature sensor  90  during step  410 . As an example, controller  56  can receive a signal from first temperature sensor  90  each time first temperature sensor  90  cycles, and controller  56  can tally or sum the number of cycles of first temperature sensor  90  during step  410  in order to determine the number of cycles of first temperature sensor  90  at step  420 . As another example, controller  56  can detect heating element  42  of heating assembly  40  deactivating during step  410 . It can be inferred that first temperature sensor  90  has cycled when heating element  42  of heating assembly  40  deactivates during step  410  if controller  56  has not expressly deactivated heating assembly  40 . Thus, each time heating element  42  of heating assembly  40  deactivates during step  410 , controller  56  can infer that first temperature sensor  90  has cycled, and controller  56  can tally or sum the number of times heating element  42  of heating assembly  40  deactivates during step  410  in order to determine the number of cycles of first temperature sensor  90  at step  420 . 
     At step  430 , controller  56  determines if the number of cycles of first temperature sensor  90  from step  420  exceeds a threshold number. As an example, at step  420 , controller  56  can compare the number of cycles of first temperature sensor  90  from step  420  to the threshold number. If the number of cycles of first temperature sensor  90  does not exceed the threshold number at step  430 , controller  56  can continue to monitor first temperature sensor  90  at step  420 . Conversely, controller  56  reduces a temperature set point of second temperature sensor  92  at step  440  if the number of cycles of the first temperature sensor  90  exceeds the threshold number at step  430 . 
     The threshold number can be any suitable number. For example, the threshold number may be greater than fifteen. As another example, the threshold number may be about twenty. The threshold number may be selected in order to avoid excessive cycling of first temperature sensor  90  and premature failure of first temperature sensor  90 . In particular, by monitoring the number of cycles of first temperature sensor  90  and reducing the temperature set point of second temperature sensor  92  at step  440  if the number of cycles of first temperature sensor  90  exceeds the threshold number, method  400  can assist with limiting or preventing cycling of first temperature sensor  90  after step  440  and prevent overcycling of first temperature sensor  90  during step  410 . 
     For example, after reducing or adjusting the temperature set point of second temperature sensor  92  at step  440 , controller  56  can regulate the temperature of heated air flowing through duct  41  with second temperature sensor  92  rather than first temperature sensor  90 . Thus, the temperature set point of second temperature sensor  92  at step  440  can be selected such that cycling of first temperature sensor  90  is limited or prevented. For example, the temperature set point of second temperature sensor  92  at step  440  can be less than a tripping or cycling temperature of first temperature sensor  90 . In such a manner, method  400  limits usage of first temperature sensor  90  during step  410  and can prevent first temperature sensor  90  from approaching its estimated life time earlier than expected. Method  400  can particularly assist with hindering overuse or overcycling of first temperature sensor  90  when dryer appliance  10  is operating in the restricted condition. 
     In method  400 , controller  56  can also select an operating temperature of dryer appliance  10  based at least in part on the operating condition of dryer appliance  10 . For example, controller  56  can select the operating temperature of dryer appliance  10  from a first temperature set point and a second temperature set point. The first and second temperature set points are different than each other. The first temperature set point can correspond to the maximum operating temperature of dryer appliance  10  in the unrestricted condition. Conversely, the second temperature set point can correspond to a maximum operating temperature of dryer appliance  10  in the restricted condition. Thus, controller  56  selects the second temperature set point if the operating condition of dryer appliance  10  is the restricted condition, and controller  56  selects the first temperature set point if the operating condition of dryer appliance  10  is the unrestricted condition. By selecting the maximum operating temperature of dryer appliance  10  based upon the operating condition of dryer appliance  10 , performance of dryer appliance  10  can be improved. 
     The first and second temperature set points can be established in any suitable manner at step  410 . For example, the first and second temperature set points may be selected by a user of dryer appliance  10 . As another example, the first and second temperature set points may be selected by a manufacturer of dryer appliance  10 , e.g., during assembly or manufacture of dryer appliance  10 . 
       FIG. 5  illustrates a method  500  for operating a dryer appliance according to another exemplary embodiment of the present subject matter. Method  500  can be used to operate any suitable dryer appliance. For example, method  500  may be used to operate dryer appliance  10  ( FIG. 1 ). In particular, controller  56  ( FIG. 3 ) may be programmed to implement method  500 . 
     At step  510 , dryer appliance  10  is operated in order to dry articles within drum  26 . As an example, a user can utilize knobs  70  to activate dryer appliance  10 . In response to the user actuating knobs  70 , controller  56  can operate motor  31  to spin drum  26  and fan  49  of air handler  48  at step  510 . Controller  56  can also activate heating element  42  of heating assembly  40  to supply heated air to chamber  25  of drum  26  at step  510 . 
     At step  520 , a temperature set point of second temperature sensor  92  is set to a first temperature set point. As an example, controller  56  can set the temperature set point of second temperature sensor  92  to the first temperature set point at step  510 . With the temperature set point of second temperature sensor  92  set to the first temperature set point, controller  56  can deactivate or cycle heating assembly  40  when a temperature measurement of second temperature sensor  92  exceeds the first temperature set point during step  510 . 
     At step  530 , controller  56  determines if an operating condition of dryer appliance  10  is a restricted condition. If the operating condition of dryer appliance  10  is not the restricted condition at step  530 , controller  56  can continue to monitor temperature measurements of second temperature sensor  92  with second temperature sensor  92  set to the first temperature set point during step  510 . Conversely, controller  56  adjusts or reduces the temperature set point of second temperature sensor  92  to a second temperature set point at step  540  if the operating condition of dryer appliance  10  is the restricted condition at step  530 . 
     With the temperature set point of second temperature sensor  92  set to the second temperature set point, controller  56  can deactivate or cycle heating assembly  40  when the temperature measurement of second temperature sensor  92  exceeds the second temperature set point during step  510 . The first and second temperature set points can be any suitable temperatures. For example, the first temperature set point may be greater than the second temperature set point. Thus, in the unrestricted condition, controller  56  can operate dryer appliance  10  such that the temperature set point of second temperature sensor  92  is the first temperature set point, and controller  56  can operate dryer appliance  10  such that the temperature set point of second temperature sensor  92  is the second temperature set point in the restricted condition. When the first temperature set point is greater than the second temperature set point, articles within drum  26  can dry more quickly if controller  56  operates dryer appliance  10  such that the temperature set point of second temperature sensor  92  is the first temperature set point, e.g., due to controller  56  permitting heated air exiting outlet  82  to have a higher temperature relative to the second temperature set point. 
     It is to be appreciated that one ordinarily skilled in the art will realize that well-known methods may be applied or mechanisms used to determine or establish the operating condition of dryer appliance  10  at step  530 . As an example, a user can utilize knobs  70  to indicate the operating condition of dryer appliance  10 . As another example, the operating condition of dryer appliance  10  may be established in accordance with methods described in U.S. patent application Ser. No. 13/787,183 to Ionelia Silvia Prajescu et al. filed on Mar. 6, 2013, the disclosure of which is incorporated by reference herein. Such methods are discussed in greater detail below. 
     To assist with improving performance of dryer appliance  10 , controller  56  can determine an operating condition of dryer appliance  10  at step  530 . In particular, controller  56  can determine if the operating condition of dryer appliance  10  is the restricted condition or the unrestricted condition. For example, controller  56  can calculate a temperature change for heated air within duct  41  between a first time and a second, e.g., later, time. Controller  56  can determine that dryer appliance  10  is operating in the restricted condition or the unrestricted condition based at least in part on the temperature change for the heated air between the first and second times. In particular, controller  56  can determine that dryer appliance  10  is operating in the restricted condition if the temperature change for the heated air is greater than a threshold value between the first and second times. Conversely, controller  56  can determine that dryer appliance  10  is operating in the unrestricted condition if the temperature change for the heated air is less than the threshold value between the first and second times. 
     At step  550 , first temperature sensor  90  is monitored in order to determine a number of cycles of first temperature sensor  90 , e.g., during step  510 . As an example, controller  56  can receive a signal from first temperature sensor  90  each time first temperature sensor  90  cycles during step  510 , and controller  56  can tally or sum the number of cycles of first temperature sensor  90  during step  510  in order to determine the number of cycles of first temperature sensor  90  at step  550 . As another example, controller  56  can detect heating element  42  of heating assembly  40  deactivating during step  550 . It can be inferred that first temperature sensor  90  has cycled when heating element  42  of heating assembly  40  deactivates during step  510  if controller  56  has not expressly deactivated heating assembly  40 . Thus, each time heating element  42  of heating assembly  40  deactivates during step  510 , controller  56  can infer that first temperature sensor  90  has cycled, and controller  56  can tally or sum the number of times heating element  42  of heating assembly  40  deactivates during step  510  in order to determine the number of cycles of first temperature sensor  90  at step  550 . 
     At  560 , controller  56  determines if the number of cycles of first temperature sensor  90  from step  550  exceeds a threshold number. As an example, at step  560 , controller  56  can compare the number of cycles of first temperature sensor  90  from step  550  to the threshold number. If the number of cycles of first temperature sensor  90  does not exceed the threshold number at step  560 , controller  56  can continue to monitor first temperature sensor  90  at step  550 . Conversely, controller  56  changes or reduces the temperature set point of second temperature sensor  92  to a third temperature set point at step  570  if the number of cycles of the first temperature sensor  90  exceeds the threshold number at step  560 . 
     The threshold number can be any suitable number. For example, the threshold number may be greater than fifteen. As another example, the threshold number may be about twenty. The threshold number may be selected in order to avoid excessive cycling of first temperature sensor  90 . In particular, by monitoring the number of cycles of first temperature sensor  90  and changing the temperature set point of second temperature sensor  92  to the third temperature set point at step  570  if the number of cycles of first temperature sensor  90  exceeds the threshold number, method  500  can assist with limiting or preventing cycling of first temperature sensor  90  after step  570 . 
     For example, after changing or reducing the temperature set point of second temperature sensor  92  to the third temperature set point at step  570 , controller  56  can regulate the temperature of heated air flowing through duct  41  with second temperature sensor  92  rather than first temperature sensor  90 . Thus, the third temperature set point of second temperature sensor  92  can be selected such that cycling of first temperature sensor  90  is limited or prevented. For example, the third temperature set point of second temperature sensor  92  at step  570  can be less than a tripping or cycling temperature of first temperature sensor  90 . In such a manner, method  500  limits usage of first temperature sensor  90  during step  510  and can prevent first temperature sensor  90  from approaching its estimated life time earlier than expected. Method  500  can particularly assist with hindering overuse or overcycling of first temperature sensor  90  when dryer appliance  10  is operating in the restricted condition. 
       FIGS. 6 and 7  illustrate plots of time versus exemplary temperature measurements of second temperature sensor  92 . In  FIG. 6 , the operating condition of dryer appliance  10  is determined to be the unrestricted condition at step  530 . Thus, controller  56  monitors temperature measurements of second temperature sensor  92  with second temperature sensor  92  set to the first temperature set point after detecting the unrestricted condition in  FIG. 6 . Conversely, the operating condition of dryer appliance  10  is determined to be the restricted condition at step  530  in  FIG. 7 . Thus, in  FIG. 7 , controller  56  monitors temperature measurements of second temperature sensor  92  with second temperature sensor  92  set to the second temperature set point after detecting the restricted condition. 
     As may be seen in  FIG. 7 , during an initial portion (indicated with bracket I) of a time interval of the drying operation, a slope or first derivative of temperature measurements from second temperature sensor  92  with respect to time increases rapidly when heating assembly  40  is activated. The restricted condition may correspond to the condition of dryer appliance  10  when the slope or first derivative of temperature measurements from second temperature sensor  92  with respect to time exceeds a threshold value. Thus, the restricted condition can be detected at step  530  due to a magnitude of the slope or first derivative of temperature measurements from second temperature sensor  92  during the initial portion I of the time interval. 
     In  FIGS. 6 and 7 , first temperature sensor  90  cycles twenty times during operation of the dryer appliance  10  (indicated with bracket N). After first temperature sensor  90  has cycled twenty times, controller  56  changes or reduces the temperature set point of second temperature sensor  92  to the third temperature set point at step  570 , e.g., such that first temperature sensor  90  does not cycle for a remainder of the drying operation. Thus, in  FIGS. 6 and 7 , controller  56  utilizes second temperature sensor  92  to regulate the temperature of heated air exiting duct  41  after first temperature sensor  90  has cycled twenty times because the temperature set point of second temperature sensor  92  has been reduced to the third temperature set point. 
     The first, second and third temperature set points of second temperature sensor  92  can be established in any suitable manner. For example, the first, second and third temperature set points of second temperature sensor  92  may be selected by a user of dryer appliance  10 . As another example, first, second and third temperature set points of second temperature sensor  92  may be selected by a manufacturer of dryer appliance  10 , e.g., during assembly or manufacture of dryer appliance  10 . 
     The first, second and third temperature set points of second temperature sensor  92  can be any suitable temperatures. In certain exemplary embodiments, the first temperature set point of second temperature sensor  92  may be greater than the second temperature set point of second temperature sensor  92 . Similarly, the second temperature set point of second temperature sensor  92  may be greater than the third temperature set point of second temperature sensor  92 . As an example, the third temperature set point of second temperature sensor  92  may be less than about three hundred degrees Fahrenheit, such as about two hundred and forty degrees Fahrenheit. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.