Defrost control method for reducing freezer package temperature deviation

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 60/280,290 filed Mar. 30, 2001.

[0003] 1. Field of the Invention

[0004] 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.

[0005] 2. Related Art

[0006] 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 operating time, “run time,” or “on time.” When the timer accumulates a predetermined amount of compressor operating 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.

[0007] According to one aspect of the present invention, a method for controlling a defrosting apparatus in a refrigerator having a compressor is provided. The method comprises the steps of receiving a demand for defrosting, detecting that the compressor is presently operating, and initiating a defrost cycle after the steps of receiving and detecting.

[0008] According to another aspect of the present invention, a method of defrosting a refrigerator or freezer having a compressor and a defrost heater is provided. The method comprises the steps of operating the compressor for a duration and energizing the defrost heater based upon completion of the step of operating the compressor.

[0009] According to a further aspect of the present invention, a controller for controlling a defrosting apparatus in a refrigerator having a compressor is provided. The controller comprises a defrost determination means for determining when a defrost cycle is needed, a compressor operation detection means for determining whether the compressor is presently operating, a compressor cycle duration determining means for determining the duration of a prior and a present continuous operation cycle, and a defrost initiation means for initiating a defrost cycle based upon the defrost determination means, the compressor operation detection means and the compressor cycle duration determining means.

[0010] FIG. 1 is a schematic diagram showing the connection of components in a refrigerator adapted to perform the defrost control method according to the present invention;

[0011] FIG. 2 is a flow diagram showing an embodiment of the defrost control method according to the present invention; and

[0012] FIGS. 3a, 3b, 3cand 3dare timing diagrams illustrating operation of a compressor and defrost cycle according to the present invention.

[0013] The present invention involves a control method and apparatus for controlling a compressor and a defrost heater for a refrigerator appliance having at least one refrigeration compartment, such as a freezer, with a door. In the present invention, a defrost cycle is initiated at the end of a compressor operation, such that the compressor is operating or has recently stopped operating.

[0014] Thus, the defrost heater is turned on only when the freezer has just been cooled. In this way, the deviations of the temperature within the freezer, and of packages therein, are reduced. If the compressor is in the middle of an off cycle, the defrost cycle will not initiate until the next compressor operation.

[0015] FIG. 1 shows a wiring schematic for a refrigerator and freezer appliance having an defrost controller 10, a compressor 12, and a defrost heater 14 for carrying out one embodiment of the invention. The controller 10 is programmed to control the defrost heater to carry out the present invention, as described below, as well as acting as a timer means. Thus, one function of the controller 10 is to do the job of the electromechanical timer in the prior art, accumulating compressor operating time until it has accumulated an amount of time equal to a set defrost interval, X. However, it should be appreciated that the timing means of the present invention may be replaced by the traditional electromechanical timer as an alternative to the controller 10.

[0016] FIG. 2 is a flowchart of the operation an algorithm embodying the compressor operation dependent defrost control described above. The algorithm is designed to initiate the defrost cycle at the end of the compressor operation, by means of a calculated prediction. In step 100 the controller 10 waits for the timer means to indicate that it is time to begin a defrost cycle, at which time control is passed to step 102. In step 102, the operating condition of the compressor 12 is determined by the condition of input E3. If it is determined that the compressor 12 is currently in a operation, control passes to step 104. If the compressor 12 is not currently operating, the controller 10 waits at step 102.

[0017] In step 104, if the controller 10 determines that the compressor 12 has been operating for at least one hour, control passes immediately to step 108. If the compressor 12 has been operating for less than one hour, control passes to step 106. In step 106, if the compressor 12 has been operating for at least 75% of the last continuous compressor on time since a defrost was called for, control passes to step 108. Otherwise, the controller 10 repeats steps 102, 104 and 106 until the compressor 12 has been operating for either at least one hour or 75% of the last operating time, whichever is determined to occur first.

[0018] Once it is determined that the compressor 12 has been operating for a sufficient time and the controller 100 has proceeded to step 108, the compressor is temporarily stopped. Then, at step 110, a defrost cycle is initiated, including energizing the defrost heater 14 for a period of time, being determined in the present embodiment by a defrost termination thermostat 16. Following the completion of the defrost cycle, the algorithm is restarted at step 100.

[0019] FIGS. 3a, 3b, 3cand 3dshow examples of the operation of the present invention as timing diagrams.

[0020] In FIG. 3a, the defrost cycle will not initiate unless the compressor has been operating for a predetermined minimum compressor operating time, such as one hour. This will help ensure that the compartments and any packages contained therein are sufficiently cooled before any heating begins.

[0021] With the above parameters, in the case of a compressor operation that is repeatedly less than one hour, no defrost cycle would ever initiate. As best shown in FIGS. 3b, 3cand 3d, in order to account for this situation, the defrost cycle is alternatively initiated if the compressor has been operating for a minimum percentage of the previous compressor operation, such as 75%.

[0022] If a defrost cycle is called for and the compressor operation ends before 1 hour has passed, the defrost cycle is initiated as soon the compressor has been operating for 75% of the duration of that previous cycle. The measurement of the current operation for determining the 75% point begins when the defrost cycle is called for and the compressor is operating.

[0023] Thus, in the example of FIG. 3b, since the defrost cycle was called for after the compressor operation had already began, and the remaining time in the compressor operation was less than 75% of the previous operation, the defrost cycle did not begin until the next compressor operation.

[0024] In the example of FIG. 3c, the compressor was not operating when a defrost was called for. As soon as the next compressor operation reached 75% of the previous compressor operation, the defrost cycle was initiated.

[0025] In the example of FIG. 3d, a defrost cycle was called for during a compressor operation and the defrost cycle was initiated before the compressor operating time had reached 75% of the previous compressor operation. This occurred because the compressor operating time has reached one hour, as set forth above. Thus, the predetermined minimum operating time also acts as a maximum compressor operating time when a defrost cycle is pending.

[0026] In the above examples, the defrost cycle will not be initiated if the compressor has stopped operating before a defrost has been called for. However, it is within the scope of the present invention that the defrost heater 14 could be controlled so that a defrost cycle could be initiated during a compressor off cycle, if the compressor 12 has stopped operating within a reasonable time before a defrost cycle is called for. For example, engaging a defrost cycle after a lapse of five minutes from the end of the compressor operation would still reduce freezer temperature deviation. Another example would be to allow the defrost cycle to initiate within a predetermined percentage of a previous compressor operating time, such as 20 percent.

[0027] 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.