Abstract:
A dryer tumble drying articles includes a drum including a cavity configured to hold articles to be dried, a first motor drivingly coupled to the drum to rotate the drum, a heat source in flow communication with the cavity, and a variable speed motor drivingly coupled to a blower positioned to deliver heated air from the heat source to the cavity.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to clothes dryers and, more specifically, to a variable speed blower for clothes dryers. 
     An appliance for drying articles such as a clothes dryer typically includes a cabinet including a rotating drum for tumbling clothes and laundry articles therein. One or more heating elements heat air prior to the air entering the drum. The warm air is circulated through the drum as the clothes and laundry items are tumbled to remove moisture from the articles in the drum. See, for example, U.S. Pat. No. 6,141,887. 
     At least one known clothes dryer utilizes an open loop control system to determine an appropriate amount of time for drying a load of clothes. The drying time is determined by an operator and entered using a manual control, such as a time selector switch. For the duration of the drying time, the heating elements are activated and deactivated to maintain warm air circulation inside the drum, and for more accurate control of the dryer heating elements, a temperature sensor is sometimes used in conjunction with the heating elements. The operator selects a drying time based on the desired dryness for the clothes and based on past experience with the particular machine. A longer drying time than is necessary to fully dry the clothes is commonly selected to ensure that the clothes are fully dried. Use of more time than is needed for effective drying, however, is wasteful. 
     While heating elements are often controlled to adjust air temperature, the blower on known residential dryers is driven at a constant speed for the total drying time. This constant speed may not facilitate lowering drying time, improving dryer efficiency, and reducing electrical energy consumption. Drying time is affected by the amount of heat that can be delivered to the clothes, which is influenced by airflow through the dryer. Airflow, in turn, is affected by many parameters, such as, ducting length and the number of bends, load size, lint filter condition, etc. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a dryer for tumble drying articles includes a drum including a cavity configured to hold articles to be dried, a first motor drivingly coupled to the drum to rotate the drum, a heat source in flow communication with the cavity, and a variable speed motor drivingly coupled to a blower positioned to deliver heated air from the heat source to the cavity. 
     In another aspect, a blower control system for a tumble type dryer having a variable speed blower motor driving the blower to supply heated air to the dryer cavity through a cavity inlet and exhaust air from the dryer cavity through a cavity outlet includes at least one temperature sensor positioned to sense a temperature associated with the dryer and generate a temperature signal representative of the sensed temperature, at least one pressure sensor positioned to sense a pressure associated with the dryer and generate a pressure signal representative of the sensed pressure, and a controller operatively coupled to the at least one temperature sensor and the at least one pressure sensor and configured to receive the temperature and pressure signals and control the operation of the variable speed blower motor based on at least one of the received signals. 
     In yet another aspect, a method for controlling a variable speed blower for a clothes dryer includes installing a controller on the dryer in communication with at least one temperature sensor and at least one pressure sensor, receiving a signal in the controller from the at least one temperature and pressure sensors, and controlling the blower motor based on at least one of the received temperature and pressure signals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is perspective broken away view of an exemplary dryer appliance. 
     FIG. 2 is a perspective broken away view of a dryer appliance showing sensor locations. 
     FIG. 3 is a schematic diagram of a controller control circuit for controlling a blower in a dryer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an exemplary clothes dryer appliance  10  in which the herein described methods and apparatus may be practiced. While described in the context of a specific embodiment of dryer  10 , it is recognized that the benefits of the herein described methods and apparatus may accrue to other types and embodiments of dryer appliances. Therefore, the following description is set forth for illustrative purposes only, and the herein described methods and apparatus is not intended to be limited in practice to a specific embodiment of a dryer appliance, such as dryer  10 . 
     Clothes dryer  10  includes a cabinet or a main housing  12  including a front panel  14 , a rear panel  16 , a pair of side panels  18  and  20  spaced apart from each other by front panel  14  and rear panel  16 , a bottom panel  22 , and a top cover  24 . Within cabinet  12  is a drum or container  26  mounted for rotation around a substantially horizontal axis. A motor  44  rotates drum  26  about the horizontal axis through a pulley  43  and a belt  45 . Drum  26  is generally cylindrical in shape, having an imperforate outer cylindrical wall  28  and a front flange or wall  30  defining an opening  32  to drum  26  for loading and unloading of clothing articles and other fabrics. 
     A plurality of tumbling ribs (not shown) are provided within drum  26  to lift clothing articles therein and then allow them to tumble back to the bottom of drum  26  as the drum rotates. Drum  26  includes a rear wall  34  rotatably supported within the main housing  12  by a suitable fixed bearing. Rear wall  34  includes a plurality of holes  36  that receive hot air that has been heated by an electrical heater  40  in communication with an air supply duct  38  and duct inlet  42 . The heated air is drawn from the drum  26  by a blower fan  48  which is driven by a blower motor  54 . The air passes through a screen filter  46  which traps any lint particles. As the air passes through the screen filter  46 , it enters a trap duct seal and is passed out of the clothes dryer through an exhaust duct  50 . After the clothing articles have been dried, they are removed from drum  26  via opening  32 . 
     A cycle selector knob  70  is mounted on a cabinet backsplash  71  and is in communication with a control system  56 . Signals generated in control system  56  operate drum  26  and heating elements  40  in response to a position of selector knob  70 . Blower motor  54  is a variable speed motor that is controlled by control system  56 . 
     With reference to FIG. 2, dryer  10  includes a temperature sensor  64  at drum hot air inlet  60  operable to produce a temperature signal indicative of an inlet air temperature. A second temperature sensor  68  is operable to produce a temperature signal indicative of a drum outlet temperature in outlet duct  50 . A pressure sensor  80  is operable to produce a pressure signal indicative of air pressure in outlet duct  50 . An inverter  66  regulates the frequency of the electric current supplied to motor  54  to control the operation of motor  54 . 
     FIG. 3 is a schematic block diagram of control system  56  including a controller  90  which is in communication with temperature sensors  64  and  68  and pressure sensor  80 . Controller  90  also is in communication with drum motor  44 , inverter  66 , and variable speed motor  54 . Controller  90  is programmed to perform functions described herein, and as used herein, the term controller is not limited to just those integrated circuits referred to in the art as controllers, but broadly refers to microprocessors, computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, field programmable gate arrays, and other programmable circuits, and these terms are used interchangeably herein. 
     In operation, a user selects a drying cycle through control system  56 . Controller  90  then controls motor  54  to vary the speed of blower fan  48 . Controller  90  contains multiple program algorithms associated with the drying options available to the user through control system  56 . For example, in one drying cycle controller  90  directs inverter  66 , controlling the duty cycle of inverter  66 , to maintain blower fan  48  at a constant speed. For another drying cycle, controller  90  directs inverter  66  to vary the speed of blower fan  48  based on temperature feedback from one or both of temperature sensors  64  and  68 . For another drying cycle, controller  90  signals inverter  66  to vary the speed of blower fan  48  based on pressure feedback from pressure sensor  80 . 
     In another embodiment, controller  90  directs inverter  66  to operate motor  54  at a constant torque. In this mode, inverter  66  is similar to a pressure sensor in that inverter  66  automatically responds to varying pressures. Factors that affect pressure within duct  50  include lint buildup or a length of outlet duct  50 , including the venting distance to the outside of the home for establishing an optimal drying time. In another drying cycle, an algorithm directs controller  90  to control motor  54  based on a combination of temperature signals from drum inlet temperature sensor  64  and drum outlet temperature sensor  68  and pressure sensor  80  to vary airflow from blower fan  48  to facilitate a reduction in drying time. 
     In another embodiment, controller  90  is programmed to determine a ducting pressure loss based on the pressure signal from pressure sensor  80  and regulate the operation of motor  54  based on the determined ducting pressure loss. In one embodiment, controller  90  regulates the operation of motor  54  based on the outlet temperature of drum  26  to maintain a constant inlet air temperature setpoint for drum  26 . In yet another drying cycle, controller  90  is programmed to regulate the operation of motor  54  based on a signal indicative of clothes load (e.g. weight) in drum  26 . 
     Optionally, motor  54  may be a self governing motor that varies speed based on load such as a high slip induction motor. In this case, the dryer would not include an inverter. 
     From the preceding, it is shown that various methods are available to control variable speed blower motor  54 . In an exemplary embodiment, control system  56  receives a signal from temperature sensor  68  and pressure sensor  80 , and control system  56  controls the operation of blower motor  54  based on the received pressure and temperature signals. One method also includes controlling blower motor  54  based on the load size in drum  26 . Load size can be selectively set by the user or automatically determined by measuring an increase of the weight of drum  26  due to the clothes load. One method also includes controlling blower motor  54  to maintain a constant inlet air setpoint for the dryer. 
     In describing one method in more detail, controller  90  executes one of several algorithms stored therein to control blower motor  54  based on the selection of a drying cycle by the user of the dryer. Controller  90  controls the operation of blower motor  54  based on the received temperature and pressure signals and load size indications. In one embodiment, inverter  66  is operatively coupled to blower motor  54  wherein control of blower motor  54  is accomplished by controlling the duty cycle of inverter  66  based on temperature. In an exemplary embodiment, control system  56  directs inverter  66  to control motor  54  at a constant torque and varies the duty cycle to inverter  66  based upon sensed temperature to adapt to different pressures for different ducting conditions while also controlling inverter  66  based on temperature. 
     The embodiments thus described provide a clothes dryer with a variable speed blower motor that allows the dryer to be operated in a manner that facilitates improving dryer efficiency, reducing energy consumption, and lowering drying time which also facilitates extending the useful life of the dryer. In varying the blower speed, the capability is provided to compensate for such factors as ducting length and the number of bends, load size and lint filter conditions to facilitate delivering more heat to the clothes. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.