Patent Publication Number: US-2023140235-A1

Title: Method Of Detection For An Over-Loaded Drying Capacity In A Clothes Dryer Or A Combo Washer-Dryer Dryer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application Claims the Benefit of U.S. Provisional Application No. 63/274,987, filed on Nov. 3, 2021. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a device and method of controlling load volume in a laundry appliance such as dryer or combination washer/dryer appliance. 
     BACKGROUND 
     When washing and drying clothes in either a washer/dryer pair or a single combination washer/dryer appliance, it is desirable to have the clothes as wrinkle fee as possible after drying has taken place. The biggest problem with drying clothes is the size of the wet load volume, added to the dryer. If a proper amount of wet clothes is added into the dryer, drying will occur, with the clothes experiencing a limited amount of wrinkles. If the dryer is overloaded with wet clothing, the clothing, after drying, ends up very wrinkled. Especially in a washer/dryer combination, where only one drum exists, it is particularly important to ensure that the wet clothes volume load is proper. 
     Generally, in a washer/dryer pair, the dryer capacity is larger than the washer capacity. This is an attempt to provide a wet clothes load volume that is proper to add into the dryer. During drying, the clothes are tumbled. As the clothes dry, they expand in the drum. This reduces the airflow in the drum which, in turn, reduces performance. Accordingly, if the dryer is overloaded with a wet load volume, the clothing will end up very wrinkled. 
     In a washer/dryer combo, only one drum is present. Thus, it is of utmost importance that the drum is not overloaded during the washing cycle. Thus, proper airflow can be achieved and moved through the drum to provide optimum drying performance. Thus, it is important for the drum to be loaded at 50-60% capacity in order to provide a proper drying without the clothes ending up wrinkled. 
     Accordingly, it is an object of the present disclosure to overcome the disadvantages of the prior art. The present disclosure provides a device and method of controlling the load volume of items or clothes loaded into a drying appliance. Specifically, the west load volume positioned within the drum of the drying appliance is monitored. 
     SUMMARY 
     According to an object of the present disclosure, a method of controlling a wet load volume loaded into a drying appliance comprises determining a volume of wet items to be positioned into the drying appliance. The wet items are positioned into the drying appliance. The volume of wet items in the drying appliance are sensed. The volume of wet items in the drying appliance is determined. A condition of the drum of the drying appliance is actively monitored. A proper volume of clothes is determined to be present in the drum of the drying appliance. The drying cycle is terminated if a proper volume of items in the drum is exceeded. Airflow, pressure drop or evaporation rate may be monitored in the drum during operation to determine if a proper load volume is present in the drum. Power draw on a fan motor associated with providing airflow to the drum during operation may be monitored to determine the proper load volume. Additionally, monitoring of sound within the drum to detect sound variation of the volume of items in the drum during operation may occur. Motor torque signal monitoring of the drum motor may occur during operation to determine the volume of items within the drum. 
     According to another aspect of the disclosure, a method of controlling a load volume of laundry in a laundry drying appliance is provided. The method includes the steps of: sensing a condition of the laundry drying appliance that is indicative of the load volume of laundry in the laundry drying appliance by receiving and processing one or more electrical signals from one or more sensors or electrical components positioned within the laundry drying appliance; determining the load volume of laundry in the laundry drying appliance based on the condition of the laundry drying appliance that is indicative of load volume; and determining if the load volume of laundry present in the laundry drying appliance exceeds a pre-determined maximum load volume value for a particular drying cycle of the laundry drying appliance. 
     The displacement of the drum during loading may be monitored to determine the load volume added into the drum. Image sensing of the items position into the drying appliance may be utilized to determine the load volume in the drum. A basket volume with items, may be sensed outside of the drum to estimate the load volume prior to entering the drum. A basket with a proper load volume may be provided within the drum. 
     According to another aspect of the disclosure, a drying appliance comprises a cabinet with an opening enabling access inside the cabinet. A door is coupled with the cabinet. The door covers the opening. A heating unit is provided inside of the cabinet and a drum receives items to be dried in the drying appliance. The drum is expandable and retractable to provide a desired volume in the drum. The drying appliance is a combination washing/drying machine. The drum has a smaller volume during washing and expands to have a larger volume during drying. 
     In accordance with another aspect of the present disclosure, a laundry drying appliance is provided, comprising: a cabinet with an opening enabling access inside the cabinet; a door coupled with the cabinet, the door covering the opening; a heating unit configured to heat air inside of the cabinet; a drum configured to receive laundry to be dried in the drying appliance; a control panel with a user interface that is configured to permit user selection of a desired drying cycle; and a controller integrated with or arranged in electronic communication with the control panel. 
     The controller is programmed to: (1) process one or more electrical signals that are received from one or more sensors or electrical components positioned within the cabinet to detect a condition of the laundry drying appliance that is indicative of load volume, (2) determine the load volume of laundry in the drum based on the condition of the laundry drying appliance that is indicative of load volume, and (3) determine if the load volume of laundry present in the drum exceeds a pre-determined maximum load volume value for the desired drying cycle. 
     According to another aspect of the disclosure, a drying appliance comprises a cabinet with an opening enabling access inside the cabinet. A door is coupled with the cabinet to cover the opening. A heating unit provides heat inside of the cabinet and a drum receives items to be dried in the drying appliance. A basket is in the drum for receiving a load volume of items. The basket is removable from the drum. The basket provides a proper amount of items, load volume, to be dried by the drying appliance. The basket can be rigid or flexible. The drying appliance is a combination washer/dryer. 
     In accordance with another aspect of the present disclosure, a washer/dryer combination appliance is provided, comprising: a cabinet with an opening enabling access inside the cabinet; a door coupled with the cabinet, the door covering the opening; a heating unit configured heat air inside of the cabinet; a tub suspended within the cabinet; a drum rotatably supported within the tub, the drum configured to receive laundry to be washed and dried in the washer/dryer combination appliance; a control panel with a user interface that is configured to permit user selection of a desired drying cycle; and a controller integrated with or arranged in electronic communication with the control panel. 
     The controller is programmed to: (1) process one or more electrical signals that are received from one or more sensors or electrical components positioned within the cabinet to detect a condition of the laundry drying appliance that is indicative of load volume, (2) determine the load volume of laundry in the drum based on the condition of the laundry drying appliance that is indicative of load volume, and (3) determine if the load volume of laundry present in the drum exceeds a pre-determined maximum load volume value for the desired drying cycle. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG.  1    is a front perspective view of an exemplary laundry appliance; 
         FIG.  2    is a schematic diagram showing a side cross-section view of an exemplary dryer; 
         FIG.  3    is a schematic diagram showing a side cross-section view of an exemplary combination washer/dryer appliance; 
         FIG.  4    is a schematic diagram showing a side cross-section view of another exemplary combination washer/dryer appliance; 
         FIG.  5    is a front perspective view of an exemplary drum for a laundry drying appliance; 
         FIG.  6    is a flow diagram of an exemplary method for determining load size and an over loaded condition in the drum based on motor torque; 
         FIG.  7 A  is a plot illustrating motor torque and rotational speed curves for different load sizes of laundry in the drum at a ramp rate of 5 RPMs per second; 
         FIG.  7 B  is a plot illustrating other motor torque and rotational speed curves for different load sizes of laundry in the drum where the ramp rate is 10 RPMs per second; 
         FIG.  7 C  is a plot illustrating other motor torque and rotational speed curves for different load sizes of laundry in the drum where the ramp rate is 15 RPMs per second; 
         FIG.  7 D  is a plot illustrating other motor torque and rotational speed curves for different load sizes of laundry in the drum where the ramp rate is 20 RPMs per second; 
         FIG.  7 E  is a plot illustrating other motor torque and rotational speed curves for different load sizes of laundry in the drum where the ramp rate is 25 RPMs per second; 
         FIG.  8    is a flow diagram of an exemplary method for determining load size in the drum based on the output of weight sensors located in the dampers; 
         FIG.  9    is a plot illustrating a calibration curve for different load sizes of laundry in the drum; 
         FIG.  10    is a flow diagram of an exemplary method for determining load size and a flow obstruction condition in the drum based on exhaust temperature; 
         FIG.  11    is a plot illustrating exhaust temperature and time curves for different load sizes of laundry in the drum and different airflow conditions; 
         FIG.  12    is a flow diagram of an exemplary method for determining load size in the drum based on evaporation rate; 
         FIG.  13    is a plot illustrating evaporation rate and time curves for different load sizes of laundry in the drum and different airflow conditions; 
         FIG.  14    is a flow diagram of an exemplary method for determining load size and an overload condition in the drum based on the output of force sensors located in the drum; 
         FIG.  15 A  is a plot illustrating a force and time curve for a small load size of laundry in the drum; 
         FIG.  15 B  is a plot illustrating a force and time curve for a medium load size of laundry in the drum; and 
         FIG.  15 C  is a plot illustrating a force and time curve for a large load size of laundry in the drum. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Turning to the figures, a laundry drying appliance is illustrated and designated with the reference numeral  10 . The laundry drying appliance  10  includes a cabinet  12  and a door  14  to enable access inside the cabinet  12 . A control panel  16  is present on the cabinet  12  for providing a user interface. A drum  20  is positioned inside of the cabinet  12  to receive a load volume of laundry to be dried. The laundry drying appliance  10  that is illustrated in  FIGS.  1  and  2    is a dryer only and includes a controller  22  for controlling the various cycles, components and the like of the laundry drying appliance  10 . 
     With reference to  FIG.  2   , the laundry drying appliance  10  also includes a heater  24 , which heats air within the cabinet  12  before it passes through holes or apertures in the drum  20  to heat the load volume of laundry within the drum  20 . The drum  20  includes baffles or lifters  26  to assist in lifting or moving the laundry in the drum during tumbling operations. A drum motor  28  positioned inside the cabinet  12  is coupled to and rotates the drum  20 . An exhaust system  30  includes a lint screen  32  within an exhaust duct  34 . The exhaust duct  34  also includes a fan  36  and an exhaust outlet  38 . The fan  36  pulls air in and through the entire exhaust system  30  so that lint can be caught in the lint screen  32  and air can be blown out through the exhaust outlet  38 . 
     Various types of sensors  40   a - 40   i  may be positioned throughout the laundry drying appliance  10  to monitor the load volume of wet laundry positioned in the drum  20 . The sensors  40   a - 40   i  are electronically coupled with the controller  22  to enable the determination that a proper load volume of wet laundry is positioned in the drum  20 . The sensors  40   a - 40   i  actively monitor the condition of the laundry drying appliance  10  before and during operation. Sensors  40   c,    40   f,    40   g  may detect the airflow, pressure drop or evaporation rate of the airflow within the drum  20  during operation to, in turn, determine proper load volume. Additionally, the sensor  40   c  may monitor the power draw of the fan  36  associated with the exhaust system  30  during operation to, in turn, determine proper load volume. The sensor  40   a  may monitor the sound within the drum  20  to detect sound variation of the load volume of laundry tumbling within the drum  20  during operation to, in turn, determine the proper load volume. For example, the sound of laundry tumbling within the drum  20  may have a higher frequency when the drum  20  is has a large load volume compared to a small load volume, such that the frequency of the sound coming from the drum  20  can be processed to estimate the load size. Additionally, the sensor  40   b  may monitor the motor torque signal of the drum motor  28  during operation to, in turn, determine proper load volume. Further, sensors  40   h,    40   i  may monitor the displacement of the drum  20  during loading of the drum  20  with the load volume of laundry to, in turn, determine proper load volume. 
     Additionally, an image sensor  50  may be present in the laundry appliance  10 . The image sensor  50  may sense individual items of laundry as they are added into the drum  20 . As shown in  FIG.  2   , the image sensor  50  may also sense a basket  52  positioned in front of the laundry drying appliance  10 . The image sensor  50  may estimate the load volume of the laundry contained in the basket  52  to, in turn, determine proper load volume. As shown in  FIG.  4   , the image sensor  50  may alternatively be positioned with a line of sight pointing towards a rear wall  21  of the drum  20 . The drum  20  may be made of metal such that the rear wall  21  of the drum  20  is shiny and therefore has high optical contrast compared to a typical load of laundry. The image sensor  50  may be used to image/detect a bright area or number of bright pixels associated with the drum  20  or rear wall  21  when the drum  20  is empty. The image sensor  50  may then be used to image/detect the bright area or number of bright pixels associated with the drum  20  or rear wall  21  when the drum  20  is loaded. Because the laundry in the drum  20  will obstruct/cover some of the bright area or number of bright pixels associated with the drum  20  or rear wall  21 , the load size can be estimated based on the percentage change in the bright area/number of bright pixels. The controller  22  may be configured to display an overload warning on the control panel  16  if the change in the bright area/number of bright pixels detected by the image sensor  50  during loading exceeds a predetermined threshold. For example, the predetermined threshold may be when ⅝ or more of the detected bright area or number of bright pixels become obscured. 
     Additionally, a basket  52  having a proper load volume for laundry to be positioned within the laundry drying appliance  10  may be included with and removable from the laundry drying appliance  10 . The amount of laundry would be first placed into the basket  52  and then into the drum  20  to provide the proper volume load in the drum  20 . 
     Additionally, sensors  40   d,    40   e  may be present in the baffle or lifter  26  to determine the amount of force exerted on the baffle or lifter  26  during operation to, in turn, determine the proper load volume. 
     The laundry drying appliance illustrated in  FIG.  3    is a combination washer/dryer appliance  10 ′. Thus, it should be appreciated that the laundry drying appliance may perform drying cycles only, such as the case with the laundry drying appliance  10  illustrated in  FIGS.  1  and  2   , or may perform both washing and drying cycles, like the combination washer/dryer appliance  10 ′ illustrated in  FIG.  3   . The items identified above in connection with the laundry drying appliance  10  that perform a similar function in the combination washer/dryer  10 ′ are designated with the same reference numerals. 
     The washer/dryer combination appliance  10 ′ includes a tub  60  that is positioned about the drum  20 . The tub  60  is suspended inside the cabinet  12 . The drum  20  rotates within the tub  60 , but the tub  60  does not rotate within the cabinet  12 . A pump  62  is positioned inside the cabinet  12  below the drum  20  and is configured to recycle/recirculate water within the tub  60  and, in turn, drum  20 . Sensors  40   a - 40   i  and image sensor  50  are contained within the washer/dryer combination appliance  10 ′ like in the laundry drying appliance  10  as previously discussed. 
     Optionally, a basket  70  may be positioned within the washer/dryer combination appliance  10 ′. The basket  70  may be secured with the lifters  26  on the drum  20 . The basket  70  may be flexible or rigid. Thus, a load volume of laundry would be placed in the basket  70 . The laundry would be washed and dried in a single cycle. Additionally, the image sensor  50  could be utilized to sense that the basket  70  is full with a proper load volume. An interface with the user, via the control panel, would indicate that a proper load volume is ready to be positioned into the drum  20 . 
     The laundry drying appliance illustrated in  FIG.  4    is a combination washer/dryer appliance  10 ″, which may perform both washing and drying cycles, like the combination washer/dryer appliance  10 ′ illustrated in  FIG.  3   . The items identified above in connection with the combination washer/dryer appliance  10 ′ that perform a similar function in the combination washer/dryer  10 ″ are designated with the same reference numerals. 
     The washer/dryer combination appliance  10 ″ includes a tub  60  that is positioned about the drum  20 . The tub  60  is suspended inside the cabinet  12  by a combination of biasing members  72  (e.g., springs) and dampers  74 . The tub  60 , biasing members  72 , and dampers  74  form a spring-mass-damper system that permits the tub  60  to move and oscillate to a limited degree within the cabinet  12 . Thus, the drum  20  rotates within the tub  60 , but the tub  60  does not rotate within the cabinet  12 . A pump  62  is positioned inside the cabinet  12  below the drum  20  and is configured to recycle/recirculate water within the tub  60  and, in turn, drum  20 . Sensors  40   a - l  and image sensor  50  are contained within the washer/dryer combination appliance  10 ″ like in the combination washer/dryer appliance  10 ′ as previously discussed. However, the washer/dryer combination appliance  10 ″ illustrated in  FIG.  4    is different in that it does not include the optional basket  70  shown in  FIG.  3   . 
       FIG.  5    illustrates an expandable drum  20 ′. The drum  20 ′ may include moveable panels  80  to enable the drum  20 ′ to expand and retract. In a combination washer/dryer appliance  10 ′, the drum  20 ′ would be arranged in a smaller volume configuration during the washing cycle. The drum  20 ′ would then expand to a larger volume configuration before or during the drying cycle to provide the desired load volume for washing and, in turn, the desired load volume for drying. Additionally, the expandable and retractable drum  20 ′ could be utilized in a drying only laundry appliance (i.e., a dryer). Here, the drum  20 ′ would be arranged in the smaller volume configuration before the drying cycle commence when a user places the wet load volume of laundry into the drum  20 ′. Upon activation of the drying cycle, the drum  20 ′ would expand to provide a proper volume size for the drum for drying purposes. 
     The image sensor  50  may detect the number or size of the items of laundry positioned in the drum  20  and provide a user with a signal that the drum  20  was at a proper load volume level or is overloaded. Alternatively, the image sensor  50  could view the basket  52  and indicate that the basket  52  is at a proper load volume for the drum and/or has oversized dimensions. 
     The volume of wet laundry in the drum  20  may be actively monitored during operation of the laundry appliance  10 . Sensors  40   c,    40   f,    40   g  may continuously or periodically monitor the airflow, pressure drop, and/or evaporation rate in the drum  20  and any or all of this information may be utilized to determine if a proper load volume is present in the drum  20 . If a proper load is not present, then the user would be notified, via a user interface on the control panel  16 , to choose another cycle or to remove some of the laundry from the drum  20 . Thus, the user would be going through a learned behavior as to the proper amount of laundry to be added into the laundry appliance  10  to provide optimal drying of the items with minimal wrinkling. 
     Additionally, sensor  40   c  could monitor the power draw of the fan motor to determine the load volume. Likewise, sensors  40   a  could monitor the sound within the drum  20  to detect sound variation of the load volume to determine if a proper load is present. 
     Sensors  40   b  could monitor the motor torque signal of the drum motor  28  during operation to determine if a proper load is positioned within the drum  20 . Additionally, drum displacement could be monitored during loading by sensors  40   h  and  40   i,  which could be optical sensors or nearfield magnetic sensors configured to measure the position of the drum  20  or may be displacement sensors mounted in or on the dampers  74 . The displacement of the drum  20  would determine if a proper load volume is present and if this amount is exceeded, a signal would be transmitted to the user. 
     Thus, various sensed characteristics prior to the operation of the drying appliance as well as actively monitoring characteristics during operation can be utilized to determine if a proper load volume has been positioned within the drum  20 . Thus, the operation of the laundry appliance  10  is carried out with the goal of providing optimal clothes drying as well as the least amount of wrinkling during the drying process. 
     The present disclosure provides several exemplary methods of controlling the load volume of laundry in the laundry drying appliances  10 ,  10 ′,  10 ″ described above. All of these exemplary methods generally follow the following steps or routine. The routine begins with the step of sensing a condition of the laundry drying appliance  10 ,  10 ′,  10 ″ that is indicative of the load volume of laundry in the drum  20 ,  20 ′ of the laundry drying appliance  10 ,  10 ′,  10 ″ by receiving and processing one or more electrical signals from one or more sensors  40 ,  50  or electrical components, such as the drum motor  28  or fan  36 , which are all positioned within the laundry drying appliance  10 ,  10 ′,  10 ″. The method proceeds with the step of determining the load volume of laundry in the laundry drying appliance  10 ,  10 ′,  10 ″ based on the condition of the laundry drying appliance  10 ,  10 ′,  10 ″ that is indicative of load volume. The method then performs the step of determining if the load volume of laundry present in the laundry drying appliance  10 ,  10 ′,  10 ″ exceeds a pre-determined maximum load volume value for a particular drying cycle of the laundry drying appliance. The pre-determined maximum load volume may be stored in memory, such as the memory of the control panel  16  or separate controller  22 , and the particular drying cycle that is considered may be any one of the drying cycles programmed into the memory of the control panel  16  or controller  22 , and the particular drying cycle that has been selected by a user via the control panel  16 . 
     One exemplary method of controlling the load volume of laundry in the drum  20  of a laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIG.  6   , which is a flow diagram of an exemplary method for determining load size and an over loaded condition in the drum  20 ,  20 ′ based on motor torque. The motor torque may be obtained from the drum motor  28  directly or sensor  40   b  by processing one or more signals generated by the drum motor  28  of sensor  40   b,  which are indicative of current draw of the drum motor  28  and motor speed (i.e., RPMs). The method begins with step  100  of powering on the laundry drying appliance  10 ,  10 ′,  10 ″ and progressively/gradually ramping up the rotational speed of the drum  20 ,  20 ′. The method then proceeds to step  102  of checking/measuring/monitoring the motor torque between 400 and 500 revolutions per minute (RPMs). In accordance with step  102 , a measured motor torque value Tq is obtained by receiving and processing one or more signals generated by the drum motor  28  of sensor  40   b  which are indicative of current draw of the drum motor  28  and/or motor speed (i.e., RPMs). The method continues with step  104  of comparing the measured motor torque value Tq obtained at step  102  to one or more motor torque benchmark values Tq 0 -Tq 3 . The motor torque benchmark values Tq 0 -Tq 3  are predetermined values that are set by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ and will therefore vary from one appliance to another. In the illustrated example, the motor torque benchmark values Tq 0 -Tq 3  include a motor torque benchmark value Tq 0  that corresponds with an overload condition (where effective drying cannot occur or where effective drying cannot occur without excessive wrinkling), a motor torque benchmark value Tq 1  value that corresponds with a large load condition, a motor torque benchmark value Tq 2  value that corresponds with a medium load condition, and a motor torque benchmark value Tq 3  value that corresponds with a small load condition. By determining whether the measured motor torque value Tq is greater than the various motor torque benchmark values Tq 0 -Tq 3 , the method determines at step  106  whether the load volume of laundry in the drum  20 ,  20 ′ of the laundry drying appliance  10 ,  10 ′,  10 ″ is too large for the laundry drying appliance  10 ,  10 ′,  10 ″ (i.e, an overloaded condition) or corresponds to a large load, a medium load, or a small load. The method may include triggering an overload warning at step  109  if an overload condition is determined at step  106 . The overload warning may be displayed to a user on the control panel  16  and/or may disable all or some drying cycles, making them unavailable until the load size is reduced. The method may also include highlighting and/or enabling a recommended cycle setting on the control panel  16  at step  110 . 
     An exemplary testing process for determining the motor torque benchmark values Tq 0 -Tq 3  by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIGS.  7 A- 7 E , which are a series of plots illustrating motor torque and rotational speed curves for different load sizes of laundry in the drum. In  FIGS.  7 A- 7 E , motor torque in Newton meters (Nm) is shown on the vertical y-axis and rotational speed in revolutions per minute (RPMs) is shown on the horizontal x-axis. The various curves correspond to 0, 5, 10, 15, 20, and 25 kilogram (kg) loads of laundry, where the heavier load sizes correspond to higher motor torque values. In  FIG.  7 A , the rotational speed of the drum  20 ,  20 ′ was increased at a ramp rate of 5 RPMs per second. The testing shows that at the 5 RPMs per second ramp rate, the resolution between the various load size curves is small (i.e., they are close together and/or overlap at some rotational speeds). In  FIG.  7 B , the rotational speed of the drum  20 ,  20 ′ was increased at a ramp rate of 10 RPMs per second. In  FIG.  7 C , the rotational speed of the drum  20 ,  20 ′ was increased at a ramp rate of 15 RPMs per second. In  FIG.  7 D , the rotational speed of the drum  20 ,  20 ′ was increased at a ramp rate of 20 RPMs per second. Finally, in  FIG.  7 E , the rotational speed of the drum  20 ,  20 ′ was increased at a ramp rate of 25 RPMs per second. These plots show that for the particular laundry drying appliance  10 ,  10 ′,  10 ″ that was tested, the resolution between the motor torque and rotational speed curves generally improves as the ramp rate is increased, but that some hysteresis starts occurring at high rotational speeds (between 800 and 1000 RPMs) and a ramp rate of 25 RPMs per second ( FIG.  7 E ). Therefore, it was determined that the motor torque benchmark values Tq 0 -Tq 3  for this particular laundry drying appliance  10 ,  10 ′,  10 ″ should be set at a rotational speed between 400 to 500 RPMs and a ramp rate of 15 RPMs per second ( FIG.  7 C ). 
     Another exemplary method of controlling the load volume of laundry in the drum  20  of a laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIG.  8   , which is a flow diagram of an exemplary method for determining load size in the drum  20 ,  20 ′ based on the output of weight or displacement sensors  40   h,    40   i  located in the dampers  74 . The method begins with step  200  of powering on the laundry drying appliance  10 ,  10 ′,  10 ″ and placing (i.e., loading) laundry into the drum  20 ,  20 ′. The method then proceeds to step  202  of checking/measuring/monitoring the weight (i.e., force) applied to the dampers  74  and/or the amount of displacement of the dampers  74 . In accordance with step  202  a weight/displacement value W indicating the weight and/or displacement measured at the dampers  74  is obtained by receiving and processing one or more signals generated by sensors  40   h,    40   i,  which are indicative of the weight/force applied to the dampers  74  or the displacement/travel of the dampers  74  experienced during loading. The method continues with step  204  of comparing the measured weight/displacement value W obtained at step  202  to one or more motor weight/displacement benchmark values W 1 -W 3 . The weight/displacement benchmark values W 1 -W 3  are predetermined values that are set by a calibration curve that is generated by testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ and will therefore vary from one appliance to another. In the illustrated example, the weight/displacement benchmark values W 1 -W 3  include a weight/displacement benchmark value W 1  that corresponds with a large load condition, a weight/displacement benchmark value W 2  value that corresponds with a medium load condition, and a weight/displacement benchmark value W 3  value that corresponds with a small load condition. By determining whether the measured weight/displacement value W is greater than the various weight/displacement benchmark values W 1 -W 3 , the method determines at step  206  whether the load volume of laundry in the drum  20 ,  20 ′ of the laundry drying appliance  10 ,  10 ′,  10 ″ corresponds to a large load, a medium load, or a small load. The method may also include highlighting and/or enabling a recommended cycle setting on the control panel  16  at step  208 . 
     An exemplary testing process for determining the weight/displacement benchmark values W 1 -W 3  by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIG.  9   , which is a plot illustrating a calibration curve for different load sizes of laundry in the drum  20 ,  20 ′. In  FIG.  9   , sensed weight in kilograms (kg) is shown on the vertical y-axis and actual weight in kilograms (kg) is shown on the horizontal x-axis. The various data points on the plot correspond to various loads of pre-weighed laundry ranging from 0 to 8 kilograms (kg). This curve is then used to calibrate the readings/measurements obtained from the sensors  40   h,    40   i  located on or in the dampers  74 . 
     Another exemplary method of controlling the load volume of laundry in the drum  20  of a laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIG.  10   , which is a flow diagram of an exemplary method for determining load size and a flow obstruction condition in the drum  20 ,  20 ′ based on exhaust temperatures, which may be obtained from temperature sensor  40   g.  The method begins with step  300  of powering on the laundry drying appliance  10 ,  10 ′,  10 ″ and initiating a drying cycle. The method then proceeds to step  302  of checking/measuring/monitoring the exhaust temperature after a pre-determined time interval. The duration of the pre-determined time interval is selected based on testing, which is explained in greater detail below. In accordance with step  302 , a measured exhaust temperature value T is obtained by receiving and processing one or more signals generated by the temperature sensor  40   g,  which are indicative of the exhaust temperature at the outlet of the exhaust duct  34 . The method continues with step  304  of comparing the measured exhaust temperate value T obtained at step  302  to one or more exhaust temperature benchmark values T 1 -T 4 . The exhaust temperature benchmark values T 1 -T 4  are predetermined values that are set by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ and will therefore vary from one appliance to another. The exhaust temperature benchmark values T 1 -T 4  are stored in the memory of the control panel  16  or controller  22 , in a look-up data table  316 . In the illustrated example, the exhaust temperature benchmark values T 1 -T 4  include an exhaust temperature benchmark value T 1  that corresponds with an overload condition (where effective drying cannot occur or where effective drying cannot occur without excessive wrinkling), an exhaust temperature benchmark value T 2  that corresponds with a large load condition, an exhaust temperature benchmark value T 3  that corresponds with a medium load condition, and an exhaust temperature benchmark value T 4  that corresponds with a small load condition. By determining whether the measured exhaust temperature value T is greater than exhaust temperature benchmark value T 1 , the method determines at step  306  whether the load volume of laundry in the drum  20 ,  20 ′ of the laundry drying appliance  10 ,  10 ′,  10 ″ is too large for the laundry drying appliance  10 ,  10 ′,  10 ″ (i.e, an overloaded condition). By determining whether the measured exhaust temperature value T is greater than exhaust temperature benchmark values T 2 -T 4 , the method determines at step  308  whether the load volume of laundry in the drum  20 ,  20 ′ of the laundry drying appliance  10 ,  10 ′,  10 ″ corresponds to a large load, a medium load, or a small load. The method may include stopping/terminating the drying cycle at step  310  if an overload condition is determined at step  306 . The method may further include displaying an overload or service fault code to a user on the control panel  16  if an overload condition is determined at step  306 . The method may also include step  314  of determining whether the user has selected a proper drying cycle on the control panel  16  for the load volume in the drum  20 ,  20 ′. If it is determined that an improper drying cycle for the load volume has been selected, the method may include the step of terminating the cycle, displaying a warning to the user on the control panel  16 , or autonomously changing the drying cycle to a proper drying cycle for the load volume determined at step  308 . 
     An exemplary testing process for determining the exhaust temperature benchmark values T 1 -T 4  by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIG.  11   , which is a plot illustrating exhaust temperature and time curves for different load sizes of laundry in the drum and different airflow conditions. In  FIG.  11   , exhaust temperature in degrees Celsius (° C.) is shown on the vertical y-axis and time in seconds (s) is shown on the horizontal x-axis. The various curves correspond to 1, 4, and 8 kilogram (kg) loads of laundry at high and low airflows, with and without the presence of a bypass seal that prevent air from traveling along a bypass flow path in the space between the drum  20 ,  20 ′ and the tub  60 . The resolution between the various load size curves is good after about 180 seconds. After about 350 seconds some hysteresis starts occurring at some load sizes. Therefore, it was determined that the exhaust temperate benchmark values T 1 -T 4  for this particular laundry drying appliance  10 ,  10 ′,  10 ″ should be set at a predetermined time interval of 180 seconds. 
     Another exemplary method of controlling the load volume of laundry in the drum  20  of a laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIG.  12   , which is a flow diagram of an exemplary method for determining load size in the drum  20 ,  20 ′ based on evaporation rate, which may be obtained from combined temperature and humidity sensors  40   f,    40   g  and the inlet and outlet of the exhaust duct  38 . However, it should also be appreciated that separate temperature and humidity sensors may be used. The method begins with step  400  of powering on the laundry drying appliance  10 ,  10 ′,  10 ″ and initiating a drying cycle. The method then proceeds to step  402  of checking/measuring/monitoring an evaporation rate (g_dot) after a pre-determined time interval. The duration of the pre-determined time interval is selected based on testing, which is explained in greater detail below. In accordance with step  402 , the evaporation rate (g_dot) is obtained by receiving and processing one or more signals generated by the combined temperature and humidity sensors  40   f,    40   g,  which are indicative of the exhaust temperature and humidity at the inlet and outlet of the exhaust duct  34 , and then using those values to calculate the evaporation rate (g_dot) at step  404 . The evaporation rate (g_dot) is calculated by multiplying the estimated mass flow rate in kilograms per second (kg/s) by the relative humidity ratio between the inlet and outlet of the exhaust duct  34 . The mass flow rate may be estimated based on the rotational speed of the fan  36 . The relative humidity ratio is calculated by subtracting the measured humidity ratio at the outlet of the exhaust duct  34  from the measured humidity ratio at the inlet of the exhaust duct  34 . Once the evaporation rate (g_dot) is calculated from these values, the method continues with step  404  of comparing the calculated evaporation rate (g_dot) obtained at step  402  to one or more evaporation rate benchmark values g_dot 1 -g_dot 3 . The evaporation rate benchmark values g_dot 1 -g_dot 3  are predetermined values that are set by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ and will therefore vary from one appliance to another. The evaporation rate benchmark values g_dot 1 -g_dot 3  are stored in the memory of the control panel  16  or controller  22 , in a look-up data table  412 . In the illustrated example, the evaporation rate benchmark values g_dot 1 -g_dot 3  include an evaporation rate benchmark value g_dot 1  that corresponds with a large load condition, an evaporation rate benchmark value g_dot 2  that corresponds with a medium load condition, and an evaporation rate benchmark value g_dot 3  that corresponds with a small load condition. By determining whether the calculated evaporation rate g_dot 1  is greater than the evaporation rate benchmark values g_dot 1 -g_dot 3 , the method determines at step  406  whether the load volume of laundry in the drum  20 ,  20 ′ of the laundry drying appliance  10 ,  10 ′,  10 ″ corresponds to a large load, a medium load, or a small load. The method may also include step  410  of determining whether the user has selected a proper drying cycle on the control panel  16  for the load volume in the drum  20 ,  20 ′. If it is determined that an improper drying cycle for the load volume has been selected, the method may include the step of terminating the cycle, displaying a warning to the user on the control panel  16 , or autonomously changing the drying cycle to a proper drying cycle for the load volume determined at step  408 . 
     An exemplary testing process for determining the evaporation rate benchmark values g_dot 1 -g_dot 3  by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIG.  13   , which is a plot illustrating evaporation rate and time curves for different load sizes of laundry in the drum  20 ,  20 ′ and different airflow conditions. In  FIG.  13   , evaporation rate in grams of water per minute (g/min) is shown on the vertical y-axis and time in seconds (s) is shown on the horizontal x-axis. The various curves correspond to 1, 4, and 8 kilogram (kg) loads of laundry at high and low airflows, with and without the presence of a bypass seal that prevent air from traveling along a bypass flow path in the space between the drum  20 ,  20 ′ and the tub  60 . The resolution between the various load size curves is good after about 180 seconds. After about 300 seconds some hysteresis starts occurring at some load sizes. Therefore, it was determined that the evaporation rate benchmark values g_dot 1 -g_dot 3  for this particular laundry drying appliance  10 ,  10 ′,  10 ″ should be set at a predetermined time interval of 180 seconds. 
     Another exemplary method of controlling the load volume of laundry in the drum  20  of a laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIG.  14   , which is a flow diagram of an exemplary method for determining load size and an overload condition in the drum  20 ,  20 ′ based on the output of force sensors  40   d,    40   e  located in the drum  20 ,  20 ′. The method begins with step  500  of powering on the laundry drying appliance  10 ,  10 ′,  10 ″ and initiating a tumbling cycle by rotating the drum  20 ,  20 ′. The method then proceeds to step  502  of checking/measuring/monitoring the force exerted on one or more lifters  26  in the drum  20 ,  20 ′. In accordance with step  502 , a measured force value F is obtained by receiving and processing one or more signals generated by the force sensor  40   d,    40   e,  which are indicative of the force exerted on the lifters  26  by the laundry in the drum  20 ,  20 ′ during tumbling. The method continues with step  504  of comparing the measured force value F obtained at step  502  to one or more benchmark force values F 1 -F 4 . The benchmark force values F 1 -F 4  are predetermined values that are set by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ and will therefore vary from one appliance to another. In the illustrated example, the benchmark force values F 1 -F 4  include a benchmark force value F 1  that corresponds with an overload condition (where effective drying cannot occur or where effective drying cannot occur without excessive wrinkling), a benchmark force value F 2  that corresponds with a large load condition, a benchmark force value F 3  that corresponds with a medium load condition, and a benchmark force value F 4  that corresponds with a small load condition. By determining whether the measured force value F is greater than the various benchmark force values F 1 -F 4 , the method determines at step  506  whether the load volume of laundry in the drum  20 ,  20 ′ of the laundry drying appliance  10 ,  10 ′,  10 ″ is too large for the laundry drying appliance  10 ,  10 ′,  10 ″ (i.e, an overloaded condition) or corresponds to a large load, a medium load, or a small load. The method may include triggering an overload warning at step  508  if an overload condition is determined at step  506 . The overload warning may be displayed to a user on the control panel  16  and/or may disable all or some drying cycles, making them unavailable until the load size is reduced. The method may also include highlighting and/or enabling a recommended cycle setting on the control panel  16  at step  510 . 
     An exemplary testing process for determining the benchmark force values F 1 -F 4  by drying/testing various pre-weighed loads in the laundry drying appliance  10 ,  10 ′,  10 ″ is shown in  FIGS.  15 A- 15 C , which are a series of plots illustrating force and time curves for small, medium, and large load sizes of laundry in the drum. In  FIGS.  15 A- 15 C , force in Newtons (N) is shown on the vertical y-axis and time in seconds (s) is shown on the horizontal x-axis.  FIG.  15 A  is a plot illustrating the force and time curve for a small load size of laundry in the drum  20 ,  20 ′.  FIG.  15 B  is a plot illustrating the force and time curve for a medium load size of laundry in the drum  20 ,  20 ′. Finally,  FIG.  15 C  is a plot illustrating the force and time curve for a large load size of laundry in the drum  20 ,  20 ′. The peaks shown in  FIGS.  15 A and  15 B  illustrate that for the small and medium load sizes, the laundry tumbles within the drum  20 ,  20 ′ where it is repetitively lifted and then falls away from the lifters  26  as the drum  20 ,  20 ′ rotates. Is tumbling action improves drying performance and reduces wrinkling. As can be seen in  FIG.  15 C , when a large load is placed in the drum  20 ,  20 ′, the laundry stops tumbling and we no longer see a series of peaks in the force and time curve. Under such a condition, drying performance is compromised and wrinkling is more common/significant. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.