Abstract:
A refrigerator including a freezer compartment is provided with a Stirling cycle refrigeration system including a displacer located within the freezer compartment and an external compressor which is fluidly coupled to the displacer. An electronic controller is provided to adjust a time phase relationship between the compressor and the displacer to establish a first phase condition for cooling of the freezer compartment and a second phase condition for establishing a defrost cycle for the refrigerator. The electronic controller is responsive to operator control inputs and sensor inputs. The phase relationship between the compressor and displacer is changed by substantially 180° from the first phase condition to the second phase condition.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of refrigerators and, more particularly, a refrigerator assembly incorporating a Stirling cycle refrigeration system, the operating phase of which can be electronically controlled to effect both cooling and defrosting of a freezer compartment of the refrigerator. 
     2. Discussion of the Prior Art 
     The Stirling cycle is a known type of efficient refrigeration cycle. Such a cycle functions by directing a working fluid through four repetitive operations, i.e., a heat addition operation at constant temperature, a constant volume heat rejection operation, a constant temperature heat rejection operation and a heat addition operation at constant volume. It has been previously proposed to utilize a Stirling cycle in a refrigeration system, particularly a heat pump system. However, it has also been proposed in the art to utilize a Stirling cycle for use in a refrigerator. Such a Stirling cycle arrangement would incorporate an expander having an associated expansion space piston and a pulsator which has an associated compression space piston. In a conventional Stirling cycle refrigeration system, the phase relationship between the expansion piston and the compression piston is determined by a mechanical coupling between the pistons. However, particularly in view of the desire to adjust the degree of refrigeration, it has also been proposed to electronically control the time phase relationship between the expansion and compression pistons in order to alter the cooling capacity of the overall system. That is, the phase relationship can be altered, such as by changing the driving frequency for the expander and compressor, in order to actually reduce the maximum cooling capacity. 
     Despite these advances, the use of Stirling cycle refrigeration systems has not been widely accepted, in part due to the fact that the electronic controls proposed for such Stirling cycle systems do not provide for all of the cycles incorporated in more conventional refrigeration systems. For instance, the prior art dealing with Stirling cycle refrigeration systems have not addressed providing an automatic defrosting operation. For this and other reasons, there exists a need in the art for an improved refrigerator incorporating a Stirling cycle refrigeration system which can be electronically controlled to perform multiple operations, including both cooling and defrost operations, automatically. In addition, there is need in the art for a compact Stirling cycle system for use in a refrigerator. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a refrigerator assembly incorporating a Stirling cycle refrigeration system which is electronically controlled in order to provide for both cooling and defrost cycles. More specifically, the refrigerator assembly includes a refrigerator cabinet within which defines at least a freezer compartment. The Stirling cycle refrigeration system includes a Stirling cycle compressor and a Stirling cycle displacer, with the compressor being mounted within the cabinet but outside of the freezer compartment and with the displacer being mounted within the freezer compartment. The electronic controller can alter the time phase relationship between the compressor and displacer in order to change the refrigerator between cooling and defrost cycles of operation. 
     In order to provide a compact arrangement, both the compressor and displacer are preferably formed as a housing within which is positioned a movable piston and from which projects various radially extending, spaced fins. The refrigerator is also provided with a fan which is adapted to blow air over the fins of the displacer within a freezer compartment, at least during cooling cycles. In the most preferred embodiment of the invention, a phase relationship between the compressor and displacer is changed by 180° automatically by the controller in order to switch between the cooling and defrost cycles of operation. 
     Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of the preferred embodiment thereof when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cut-away left perspective view of a side-by-side refrigerator incorporating the Stirling cycle refrigeration system of the invention; and 
     FIG. 2 is a schematic diagram of the refrigeration system constructed in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With initial reference to FIG. 1, a refrigerator constructed in accordance with the present embodiment is generally indicated at  2 . Refrigerator  2  includes a cabinet  6  including top, front, side, rear and bottom wall portions  8 - 13 . Positioned within cabinet  6 , at a lower portion thereof, is an insert panel  16  that defines a lower rear chamber  18 . 
     For purposes of this preferred embodiment, refrigerator  2  is shown to be a side-by-side refrigerator. However, at this point, it should be noted that the present invention is also applicable to other types of refrigeration units, including top-mount refrigerators and dedicated freezer units. In any event, as shown, refrigerator  2  includes a freezer compartment  21 , generally defined by a liner  23  inserted into cabinet  6 , and a fresh food compartment  26  which, in turn, is defined by a separate liner  24  inserted into cabinet  6 . In the manner known in the art, liner  23  for freezer compartment  21  and liner  24  for fresh food compartment  26  are separated by a vertical mullion (not shown) and insulated foam is injected between cabinet  6  and the respective compartment liners  23  and  24 . Furthermore, in a manner also known in the art, front portion  9  of cabinet  6  is provided with a freezer door  30  including a handle  32  for accessing freezer compartment  21 , as well as a fresh food door  35  including a handle  37  for use in selectively accessing fresh food compartment  26 . An air passageway  40  is shown to interconnect freezer compartment  21  to fresh food compartment  26  in order to enable a flow of cooling air from freezer compartment  21  to enter fresh food compartment  26 . Although not shown, an automatic damper or other air flow control arrangement is preferably provided at air passageway  40  to regulate the amount of flow between freezer compartment  21  and fresh food compartment  26  based on operator set controls and one or more temperature sensors. Since such an air flow system is widely known in the art, it will not be discussed further here. 
     In accordance with the invention, refrigerator  2  incorporates a Stirling cycle refrigeration system generally indicated in both FIGS. 1 and 2 at  52 . System  52  includes a Stirling cycle compressor  55  and a Stirling cycle displacer or expander  58  which are interconnected by a fluid coupling  61 . Each of compressor  55  and displacer  58  have associated therewith heat exchange surfaces  65  and  67  respectively. In addition, the Stirling cycle refrigeration system  52  also includes a first fan  70  associated with compressor  55  and a second fan  72  associated with displacer  58  as will be more fully discussed below. 
     As perhaps best illustrated in FIG. 2, compressor  55  includes a housing  80  within which is shiftably mounted a piston  82 . Compressor  55  also includes a phase altering actuator  85  which, in the preferred embodiment, takes the form of a linear motor. In a similar manner, displacer  58  includes a housing  89  within which is arranged a movable piston  90 . Displacer  58  also has an associated actuator  92 . As the general operation of a Stirling cycle is known in the art, including the use of linear motors to adjust the time phase relationship between a compressor and a displacer of a Stirling cycle system, these basic operation functions do not form part of the present invention and therefore will not be discussed further here. As further shown, a regenerator  94  is provided at displacer  58 . 
     In order to maintain a rather compact arrangement for Stirling cycle refrigeration system  52 , the heat exchange surfaces  65  of compressor  55  are preferably defined by a plurality of radially projecting, spaced fins which are formed as part of housing  80 . In a similar manner, heat exchange surfaces  67  are formed as fins and extend from housing  89  of displacer  58 . The arrangement of actuators  85  and  92  and heat exchange surfaces  65  and  67  of compressor  55  and displacer  58  make for an overall compact arrangement. In any event, as clearly shown in FIG. 1, compressor  55  is mounted within the lower rear chamber  18  and displacer  58  is mounted within freezer compartment  21 . Again, compressor  55  and displacer  58  of Stirling cycle refrigeration system  52  are interconnected through a coupling  61  which extends through suitable apertures (not labeled) formed in insert panel  16  and freezer liner  23 . First fan  70  is disposed adjacent compressor  55  for directing a flow of air over heat exchange surfaces  65  and second fan  72  is disposed adjacent displacer  58  for directing a flow of heat exchange surfaces  67 . 
     Refrigerator  2  also incorporates a control arrangement for refrigeration system  52 . In accordance with the most preferred embodiment of the invention, this control arrangement includes a central processing unit (CPU)  97  which is linked to both actuators  85  and  92 , as well as fans  70  and  72 . CPU  97  receives signals from operator control inputs at  102  and from sensor inputs  105 . The operator inputs in accordance with the invention generally constitute temperature controls for establishing desired temperatures within freezer compartment  21  and fresh food compartment  26 . The sensor inputs preferably include one or more temperature sensors associated with freezer compartment  21  and fresh food compartment  26 . Furthermore, the CPU incorporates a timing unit  108 , the function of which will be described more fully below. 
     During operation of the Stirling cycle refrigeration system  52  in a cooling mode, heat exchange surfaces  65  of compressor  55  will become heated while heat exchange surfaces  67  of displacer  58  will be cooled. Fan  70  is operated in accordance with the present invention to dissipate heat from compressor  55 , while fan  72  is used to develop a flow of cooling air for use in freezing food products placed within freezer compartments  21 , as well as cooling other food items placed within fresh food compartment  26 . As known in connection with Stirling cycle systems, an optimum time phase relationship between the actions of piston  82  and piston  90  can be established to maximized the heat exchange between compressor  55  and displacer  58 . A particular time phase relationship established for the invention is set by CPU  97  through actuators  85  and  92 . The established time phase relationship will be set by CPU  97  dependent upon the signals received from operator control inputs  102  and sensor inputs  105 , along with preset timing functions established in unit  108 . 
     For the most part, it is desired to operate Stirling cycle refrigeration system  52  at its maximum efficiency to arrive at desired temperature settings for freezer compartment  21  and fresh food compartment  26 . That is, the Stirling cycle refrigeration system  52  will operate until sensor inputs at  105  relay to CPU  97  that the temperatures selected at the operator control inputs  102  have been reached. During operation of the Stirling cycle refrigeration system  52 , it is preferably desired to have first and second fans  70  and  72  simultaneously running. In this manner, an efficient cooling system for refrigerator  2  is presented. 
     In accordance with a particular aspect of the invention, CPU  97  can electronically alter the time phase relationship of compressor  55  and displacer  58  by substantially 180° such that the direction of heat flow between these components is reversed whereby refrigerator  2  can enter a defrost cycle. Therefore, in accordance with the present invention, the Stirling cycle refrigeration system  52  can function not only to efficiently cool refrigerator  2  but can be readily adjusted to establish a source of heat within freezer compartment  21  in order to perform a defrosting operation. In accordance with the most preferred embodiment of the invention, CPU  97  includes timer unit  108  which determines when a defrost cycle is entered. Other types of known arrangements for establishing a defrost cycle could also be utilized, such as ice accumulation sensors, adaptive defrost and the like. 
     Although described with respect to a preferred embodiment of the invention, it should be readily understood that various changes and/or modifications could be made to the invention without departing from the spirit thereof. In general, the invention is only intended to be limited by the scope of the following claims.