Abstract:
Adaptive defrost control and method for a household refrigerator wherein a defrost heater is prevented from being powered as long as a compressor is running. The adaptive defrost control also provides a vacation mode in which the defrost interval is set to an artificially long interval if a door of refrigerator has not been opened for some predetermined period of time.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. patent application Ser. No. 09/968,669 filed Oct. 1, 2001, which claims the benefit of U.S. Provisional Application Serial No. 60/280,072 filed Mar. 30, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates generally to the control of a defrost heater for a refrigerator and specifically to an adaptive control method and apparatus therefor.  
           [0003]    It is known to provide a defrost heater to a refrigeration unit such as in a domestic refrigerator or freezer appliance. In conventional arrangements, the heater is cycled on the basis of electromechanical timers which accumulate time on the basis of compressor run time. When the timer accumulates a predetermined amount of compressor run time, the defrost heater initiates a defrost cycle, regardless of the current state of various refrigeration components and environment. This can lead to an inefficient use of energy.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a method for defrosting a household refrigeration appliance including a compressor and a refrigeration compartment having a door. Said method comprises the steps of: waiting for a defrost interval (X) based on accumulated compressor run time; initiating a defrost cycle only after both the defrost interval has elapsed and the compressor is not running; and after initiating said defrost cycle, terminating said defrost cycle as determined by a defrost termination thermostat.  
           [0005]    The present invention further provides a defrosting refrigerator, comprising: a cooling apparatus for providing cooling air to the refrigerator when operating; a defrost apparatus which operates upon initiation for a defrost period; and a controller which initiates the defrost apparatus after a set defrost interval elapses and only when the cooling apparatus is not operating.  
           [0006]    The present invention further provides a method for defrosting a household refrigeration appliance comprising the steps of: providing a control means for controlling a defrost means of the appliance; initiating a defrost cycle after a defrost interval has elapsed; adjusting the defrost interval of the control means to a vacation defrost interval, which is greater than a maximum normal defrost interval, if a door of the appliance has not been opened for a predetermined period; and resetting the defrost interval of the control means to equal or less than the maximum normal defrost interval from the vacation defrost interval when the door is opened.  
           [0007]    The present invention further provides a defrosting refrigerator comprising: a defrost apparatus; at least one compartment having a door, the door having a sensor for detecting the open or closed condition of the door; and a controller which monitors the sensor, which initially controls the defrost apparatus according to a first mode, and which controls defrost apparatus according to a second mode when the sensor indicates the door has been closed for a predetermined period, wherein the controller reverts to the first mode if the sensor indicates the 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a perspective view of a refrigerator embodying an adaptive defrost control of the present invention;  
         [0009]    [0009]FIG. 2 is a schematic view of the electrical connections of a refrigerator embodying the adaptive control of the present invention;  
         [0010]    [0010]FIG. 3 is a flow diagram for a method of performing an adaptive defrost control according to an embodiment of the present invention; and  
         [0011]    [0011]FIG. 4 is a timing chart illustrating various steps of a method of performing an adaptive defrost control according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    [0012]FIG. 1 shows a refrigerator  1  having a freezer compartment  2 . The freezer compartment  2  is provided with a door  3  having a switch  4  which monitors the condition of the door  3 , either open or closed.  
         [0013]    [0013]FIG. 2 shows an wiring schematic for the refrigerator  1  which comprises an adaptive defrost controller  10 , a compressor  12 , and a defrost heater  14 . The defrost heater  14  is provided to defrost the freezer compartment  2  of the refrigerator  1  (see FIG. 1). The controller  10  is programmed to control the defrost heater to carry out the present invention, as described below. In a sense, the controller  10  does the job of the electromechanical timer in the prior art, accumulating compressor run time until it has accumulated an amount of time equal to a set defrost interval, X. At this point the controller  10  indicates that it is time for a defrost cycle.  
         [0014]    However, the controller  10  is also programmed to adjust the value of the defrost interval X, based upon certain operating conditions. In order to reduce the above described waste of energy, the adaptive defrost controller  10  monitors the defrost time and adjusts the defrost time interval accordingly.  
         [0015]    The algorithm shown in FIG. 3 illustrates one embodiment for adjustment of the heater cycle time, X according to the present invention. First, the defrost interval X is set to be equal to a minimum or initial defrost interval, X initial , such as 6 hours (step  30 ). After the controller  10  has accumulated X hours, a defrost cycle is initiated (step  32 ).  
         [0016]    A defrost termination thermostat or controller  16  (FIG. 2) turns off the heater when sufficient defrosting has occurred. Meanwhile, the controller  10  stores the duration of the defrost cycle or defrost time, T. T range  defines the time limits for an “ideal” defrost time. For example, T range  could be a range of 12 to 16 minutes. If the defrost time, T, is greater than a maximum “ideal” defrost time, T range,max , or 16 minutes, as determined in step  34 , then the controller  10  proceeds to step  42 . Otherwise, if the defrost time, T, is less than a minimum “ideal” defrost time, T range,min , or 12 minutes as determined in step  36 , then the controller  10  proceeds to step  38 . Otherwise, if T is within the “ideal” defrost time, T range , or between 12 and 16 minutes, then the controller  10  returns to step  32  and waits for the next defrost cycle.  
         [0017]    If the controller reaches step  38 , then the defrost cycle, T, is too short for maximum efficiency. At this point, if the defrost interval X is already set to a maximum value, X max , such as 72 hours, then the controller  10  proceeds to step  46 . Otherwise, the defrost interval X is incremented by a set increment, such as 2 hours, (step  40 ) and the controller  10  returns to step  32  and waits for the next defrost cycle. This lengthening of the defrost interval, X, will help to increase the length of the subsequent defrost cycle, T.  
         [0018]    If the controller reaches step  42 , then the defrost cycle, T, is too long for maximum efficiency. At this point, if the defrost interval, X, is already set to the minimum value, X initial , then the controller  10  returns to step  32  and waits for the next defrost cycle. If, however, the defrost interval, X, is greater than X initial  then the controller decrements the defrost interval, X, by the set increment, or 2 hours, (step  44 ) before returning to step  32 .  
         [0019]    If the controller reaches step  46 , then the defrost cycle, T, is too short for maximum efficiency but the defrost time, T, is already at a maximum ideal defrost time, T range,max , or 16 minutes. If the controller  10  determines by monitoring the door switch  4  at input E 7  that the freezer door  3  has not been opened in the preceding 24 hours, vacation mode VM is entered at step  48 . Otherwise, the controller  10  returns to step  32  and waits for the next defrost cycle.  
         [0020]    Once in vacation mode VM at step  48 , the controller waits for a vacation mode time, X max,vacation , such as 160 hours, initiates a defrost cycle and then proceeds to step  50 . At step  50 , if the controller determines that the freezer door  3  has been opened while in vacation mode, the controller exits vacation mode VM via step  52 . At step  52 , the compressor  12  is run for a predetermined vacation mode exit period, such as one hour, and is followed by a defrost cycle. Following step  52 , the controller  10  exits vacation mode VM and proceeds to step  30 , resetting X to X initial .  
         [0021]    If the door is not opened at step  50 , the controller proceeds to step  54 . At step  54 , while in vacation mode VM, if the defrost cycle time, T, is below T range,max , then vacation mode VM is maintained and the controller  10  returns to step  48 . If, however, T is equal or greater than T range,max  then the controller exits vacation mode VM directly and proceeds to step  30 , resetting X to X initial .  
         [0022]    In addition to the above, an absolute maximum amount of time that the defrost heater can be on, T max , is set. During the defrost cycle, if the controller  10  determines that the heater has been on for T max , the heater is immediately terminated at output E 1 , any drip time (explained below) is skipped, and the controller returns to step  30 , allowing the compressor to restart immediately at the demand of the compressor thermostat or cold control  18 .  
         [0023]    [0023]FIG. 4 illustrates a defrost delay used in the present invention to avoid applying defrost heat to boil off liquid refrigerant which may be present in an evaporator.  
         [0024]    Ordinarily, the compressor uses energy to condense the refrigerant in a condenser, which in turn absorbs heat from refrigeration compartments causing liquid refrigerant to evaporate and thereby cooling the compartments. However, if the defrost heater is energized while the condenser contains liquid refrigerant, such as immediately following a compressor run cycle, this liquid may be evaporated by the defrost heater, rather than by energy absorbed from the refrigeration compartments.  
         [0025]    According to the present invention, in order to minimize liquid refrigerant being boiled off by the defrost heater  14 , the adaptive defrost controller  10  will not turn on the defrost heater  12  while the compressor thermostat  18  is open, indicating the compressor is running. That is, once the timing algorithm determines it is time for a defrost cycle to occur, the controller pauses and waits for the freezer compartment  2  to become sufficiently cold before starting the heater  14 . During this delay, compressed liquid refrigerant in the condenser is re-evaporated by heat energy from the freezer compartment  2 , such that the cooling is not allowed to be wasted by the defrost heater  14 .  
         [0026]    Specifically, as shown by FIG. 4, the defrost cycle is controlled by the controller as follows. The defrost interval, X, is allowed to elapse by accumulation of compressor run time during the cycling on and off of the compressor (step  60 ). At time  62 , the controller  10  determines that it is time for a defrost cycle to occur.  
         [0027]    The controller  10  waits for the compressor thermostat  18  to open, shutting the compressor  12  off at time  64 . At the same time  64 , a relay is switched to a defrost mode which, among other things, keeps the compressor  12  from turning back on. Subsequently, the controller pauses for a period of time  66  to allow evaporation of the refrigerant just compressed into liquid by the action of the compressor.  
         [0028]    Once enough heat is absorbed by the refrigerant to re-close the compressor thermostat  18  at time  68 , the defrost heater  14  is powered. The defrost heater  14  remains on for a period of time, or the defrost period, T until the defrost termination thermostat  16  turns off the heater  14 .  
         [0029]    Following the termination of the heater  14 , the controller  10  waits for a predetermined “drip time”  70  and then resumes normal compressor operation  72 .  
         [0030]    In the present embodiment, the adaptive defrost controller  10  is an electronic controller. If power to the controller  10  is interrupted for more than a few seconds, a memory circuit contained therein resets to a condition as though it had not been powered previously. Therefore, the information or data necessary for the adaptive defrost controller to operate as desired is lost. For instance, a brief power failure may interrupt a defrost cycle after the defrost heater  14  has been initiated. When power is restored, the adaptive defrost controller  10  would reset, returning to step  30  (FIG. 3) and defrosting would not resume until the defrost interval, X, has again elapsed. This could result in poor cooling performance due to the unintended extended time interval between defrosts.  
         [0031]    The defrost termination thermostat  16  of the present embodiment is of a type which operates regardless of power interruption, such as a mechanical thermostat. Therefore, the termination thermostat  16  can be used by the adaptive defrost controller as a power independent memory device. For this purpose, the controller  10  checks the condition of the termination thermostat  16  upon the initial application of power. If the termination thermostat  16  is open, the appliance is presumed to be operating from a warm or newly uncrated condition. In this case, the controller  10  starts the compressor  12  and begins normal adaptive defrost control.  
         [0032]    If the termination thermostat  16  is closed upon the application of power to the adaptive defrost controller  10 , the appliance is in a cold state and a temporary power outage condition is presumed. In this case, the compressor  12  is run for a shortened interval followed by a defrost cycle. Following this shortened defrost interval, normal adaptive defrost control is  
         [0033]    It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.