Abstract:
A refrigeration system is disposed within an outer cabinet having a freezer compartment and a fresh food compartment connected via a mullion opening. A compressor, a condenser, an expansion device and a freezer evaporator are connected in series to expand and condense a refrigerant to cool the compartments. A freezer compartment temperature sensor and a fresh food compartment temperature sensor are provided to sense compartment temperatures. A discrete speed freezer compartment fan directs cooling air throughout the freezer compartment and through the mullion opening to the fresh food compartment. A controller generates control signals to the discrete speed evaporator fan to operate at high speed if either the fresh food compartment or both the freezer and fresh food compartments demand cooling and at a low speed if only the freezer compartment demands cooling.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to refrigeration systems and more specifically to refrigeration systems with independent compartment temperature control. 
     Household refrigerators typically operate on a simple vapor compression cycle. Such a cycle typically includes a compressor, a condenser, an expansion device and an evaporator connected in series and charged with a refrigerant. The evaporator is a specific type of heat exchanger that transfers heat from air passing over the evaporator to refrigerant flowing through the evaporator, thereby causing the refrigerant to vaporize. The cooled air is then used to refrigerate one or more freezer or fresh food compartments. 
     Household refrigerators are expected to operate over a range of ambient temperatures, typically from about 55° F. to about 90° F. System users are typically supplied control knobs to adjust Fresh Food and Freezer compartment temperatures. At each combined setting of the control knobs, there is a target set of Fresh Food and Freezer temperatures that an ideal refrigerator should achieve, independent of ambient conditions. Different hardware and control strategies attempt to approximate this ideal performance matrix. 
     Typically a control device is used to regulate airflow to the fresh food compartment to account for the changing load split between freezer and fresh food sections. During high ambient temperature and frequent fresh food access, more airflow to the fresh food section is required to maintain target temperatures. Manual damper air control cannot automatically compensate for changing loads and is prone to customer misadjustment. Motorized damper airflow modulation, powered by a system controller, is prone to malfunction (i.e. freeze up) and may cause adverse temperature gradients during low ambient operation. 
     Accordingly, there is a need in the art for an improved refrigeration system for achieving ideal performance temperatures of fresh food and freezer compartments. 
     SUMMARY OF THE INVENTION 
     A refrigeration system is disposed within an outer cabinet having a freezer compartment and a fresh food compartment connected via a mullion opening. A compressor, a condenser, an expansion device and a freezer evaporator are connected in series to expand and condense a refrigerant to cool the compartments. A freezer compartment temperature sensor and a fresh food compartment temperature sensor are provided to sense compartment temperatures. A discrete speed evaporator fan directs cooling air throughout the freezer compartment and through the mullion opening to the fresh food compartment. A controller generates control signals to the discrete speed evaporator fan to operate at high speed if either the fresh food compartment or both the freezer and fresh food compartments demand cooling and to operate at low speed if the freezer compartment alone demands cooling. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The FIGURE is a schematic cross-sectional side elevation view of an illustrative embodiment of the instant invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An exemplary embodiment of a refrigeration system  10  includes an outer cabinet  11  having a Freezer compartment  12  and a Fresh Food compartment  14 , as shown in FIG. 1. A mullion  16  separates Freezer compartment  12  and Fresh Food compartment  14 . Although the present invention is described herein in connection with refrigeration system  10 , the present invention is not limited to practice with refrigeration system  10 . In fact, the present invention can be implemented and utilized with many other configurations. 
     Freezer and Fresh Food compartments  12 ,  14  typically comprise a housing formed with thermally insulated walls provided with an opening or a door for placement or removal of articles. 
     Refrigeration system  10  further comprises a compressor  18 , a condenser  20 , an expansion device  22  and an evaporator  24 . Compressor  18  is electrically coupled to a controller  25 . As is customary, refrigeration system  10  is provided in thermal association with the freezer or fresh food compartment, having several components of refrigeration system  10  mounted on or in the housing containing the freezer or fresh food compartment and adapted with the freezer and fresh food compartment  12 ,  14  to cool the interior thereof. 
     A freezer compartment temperature sensor  26  and a fresh food compartment temperature sensor  28  are disposed within freezer compartment  12  and fresh food compartment  14 , respectively, to sense compartment temperatures. Temperature sensors  26 ,  28  typically comprise solid state sensors such as resistance temperature detectors (RTD), thermocouples, thermistors or the like. Each temperature sensor  26 ,  28  is electronically coupled to controller  25 . 
     For purposes of clarity, in one embodiment, the operation of refrigeration system  10  will be discussed in terms of a FREEZER MODE and a FRESH FOOD MODE. Although exemplary embodiments will be discussed in terms of a FREEZER MODE, and a FRESH FOOD MODE, the invention is not limited to these modes. In fact, the present invention can be implemented and utilized with many other modes of operation. 
     During operation, freezer compartment temperature sensor  26  and fresh food compartment sensor  28  generate temperature signals, which temperature signals are received by controller  25 . 
     If the temperature signals (T 1 ) generated by freezer compartment temperature sensor  26  rise above a preset freezer compartment temperature, typically in the range between about −20° C. to about −15° C., controller  25  enters FREEZER MODE. 
     During FREEZER MODE, controller  25  generates a signal to activate compressor  18 , a condenser fan  30  and a freezer compartment fan  32 . In one embodiment, freezer compartment fan  32  is a two-speed fan, having two discrete fan speeds: HIGH and LOW. In another embodiment, freezer compartment fan  32  is a three-speed fan having three discrete fan speeds: HIGH, MEDUIM, and LOW. High-pressure gaseous refrigerant is discharged from compressor  18  and is condensed in condenser  20 . The now-liquid refrigerant is expanded through expansion device  22  to a lower pressure and flows to evaporator  24 . The refrigerant under low pressure, and correspondingly at a low temperature, enters evaporator  24  where the refrigerant is evaporated in a conventional manner. The evaporation of the refrigerant lowers the temperature of the air surrounding evaporator  24 . The cooled air is directed by the rotation of freezer compartment fan  32  about freezer compartment  12 . 
     If the temperature signals (T 1 ) generated by freezer compartment temperature sensor  26  drop below the preset freezer compartment temperature, cooling is no longer required and controller  25  exits FREEZER MODE. 
     If the Temperature signals (T 2 ) generate d by fresh food compartment temperature sensor  28  rise above a preset fresh food compartment temperature, typically in the range between about 3° C. to about 7° C., controller enters FRESH FOOD MODE. 
     During FRESH FOOD MODE, controller  25  generates a signal to activate compressor  18 , condenser fan  30  and freezer compartment fan  32 . High-pressure gaseous refrigerant is discharged from compressor  18  and is condensed in condenser  20 . The now-liquid refrigerant is expanded through expansion device  22  to a lower pressure and flows to evaporator  24 . The refrigerant under low pressure, and correspondingly at a low temperature, enters evaporator  24  where the refrigerant is evaporated in a conventional manner. The evaporation of the refrigerant lowers the temperature of the air surrounding evaporator  24 . The cooled air is directed by the rotation of freezer compartment fan  32  through an opening  34  in mullion  16  to fresh food compartment  14 . 
     If the temperature signals (T 2 ) generated by fresh food compartment temperature sensor  28  drop below the preset fresh food compartment temperature, cooling is no longer required and controller  25  exits FRESH FOOD MODE. 
     In accordance with one embodiment of the instant invention, the speed of freezer compartment fan  32  is changed by controller  25  depending on the cooling needs of either freezer compartment  12  or fresh food compartment  14 . A FREEZER MODE only condition indicates a low speed fan is appropriate to prevent overcooling of the fresh food compartment. A FRESH FOOD MODE only status indicates a high speed fan is appropriate to maximize cooling of the fresh food compartment while limiting overcooling of the freezer. When both modes are active, the medium fan speed is used in the three-speed embodiments, and the high speed fan is used in the two-speed embodiments. 
     One benefit derived from this invention is the elimination of the air damper between the freezer and fresh food compartments. A discreet multi-speed freezer compartment fan  32  is used instead to control the relative cooling supply between freezer compartment  12  and fresh food compartment  14 . 
     In another embodiment of the instant invention, freezer compartment fan  32  is a two-speed freezer compartment fan  32  having two discrete speeds: HIGH and LOW. High speed is the normal operating mode as high speed is a compromise between noise and peak load performance. Controller  25  activates the hermetic loop in high speed mode as this is the most efficient operating point. In this embodiment, only freezer temperature sensor  28  can activate the hermetic loop. 
     If the temperature signals (T 1 ) generated by freezer compartment temperature sensor  26  rise above the preset freezer compartment temperature, typically in the range between about −20° C. to about −15° C., controller  25  generates a signal to activate compressor  18  and freezer compartment fan  32 . Freezer compartment fan  32  is activated in high speed. 
     Next, controller  25  monitors fresh food compartment temperature sensor  28 . If the temperature signals (T 2 ) generated by fresh food compartment temperature sensor  28  are above a preset fresh food compartment temperature, typically in the range between about 3° C. to about 7° C., controller  25  maintains the speed of freezer compartment fan  32  at high. 
     If the temperature signals (T 2 ) generated by fresh food compartment temperature sensor  28  drop below the preset fresh food compartment temperature, cooling is no longer required in fresh food compartment  14 . Controller  25  then monitors freezer compartment temperature sensor  26  to determine if freezer compartment  12  still requires cooling. If freezer compartment  12  requires additional cooling, freezer compartment fan  32  is slowed to low speed until the temperature signals (T 1 ) generated by freezer compartment temperature sensor drop below the preset freezer compartment temperature, cooling is no longer required and controller  25  generates a signal to stop compressor  18  and freezer compartment fan  32 . 
     As discussed above, in this embodiment, if freezer compartment temperature sensor  26  indicates cooling of freezer compartment  12  is needed, the freezer compartment fan  32  is activated in high speed. If controller  25  monitors fresh food compartment temperature sensor  28  and fresh food compartment cooling is not required, controller  25  slows the speed of freezer compartment fan  32  to low until freezer compartment  12  is cooled. 
     In one embodiment, only freezer temperature sensor  28  can activate the hermetic loop unless an “alarm limit” is reached by fresh food compartment  14 , for example, 2° C. to 5° C. above the preset fresh food compartment temperature. If an “alarm limit” is indicated by fresh food temperature sensor  28 , freezer compartment fan  32  is started in high speed and the cooled air about evaporator  24  is directed by the rotation of freezer compartment fan  32  through opening  34  in mullion  16  to fresh food compartment  14 . 
     Freezer compartment fan  32  operating at low speed does not significantly impact the temperature of fresh food compartment  14 . The low speed operation of freezer compartment fan  32  does not generate enough flow pressure to deliver significant airflow through opening  34  in mullion  16  between freezer compartment  12  and fresh food compartment  14 . Accordingly, low speed fan operation is primarily used for low temperature ambient conditions or to trim the temperature of freezer compartment  12  lower when fresh food compartment  14  requires no cooling. 
     In another embodiment of the instant invention, freezer compartment fan  32  is a three-speed freezer evaporator fan having three discrete speeds: HIGH; MEDIUM; and LOW. Medium speed is the normal operating mode as medium speed is appropriate for normal ambient operation and provides quiet operation that is desirable for typical kitchen use. Controller  25  activates the hermetic loop in medium fan speed unless a high ambient temperature is detected or a quick chill (“turbo cool”) of fresh food compartment  14  is selected by an end-user. In each of these cases, controller  25  activates the hermetic loop in high speed as a starting speed. High speed is used to deliver maximum fresh food cooling if medium fan speed is not capable of achieving set point temperature control in fresh food compartment  14  prior to freezer compartment  12  being satisfied. Low speed is used in a manner identical to that of the two-speed evaporator fan logic. 
     In another embodiment of the instant invention, both the two-speed and the three-speed freezer compartment fan  32  embodiments use the temperature set point of freezer compartment  12  to initiate the hermetic loop cooling and the satisfaction of both freezer compartment  12  and fresh food compartment  14  set points to terminate the hermetic loop. Transition to a lower fan speed occurs when fresh food compartment  14  cooling is satisfied prior to freezer compartment  12  cooling requirements. Transition to a higher fan speed occurs when the cooling of freezer compartment is satisfied prior to the cooling of fresh food compartment  14 . 
     While only certain features of the invention have been illustrated and described, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.