Abstract:
A refrigerating apparatus includes a compressor, a condenser, a capillary and an evaporator. A bypass conduit with a valve is arranged so that the refrigerant discharged from the compressor will bypass at least the condenser and the capillary so as to return to the inlet side of the compressor. The pressure or the temperature of the refrigerant in the apparatus is sensed by a sensor. When the sensed value is less than a prescribed value, the valve is opened to return the hot gas to the compressor. The compressor is driven for elevating its temperature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a freezing apparatus and, more particularly, to a novel improvement for increasing the freezing efficiency of a rotary compressor employed in the freezing apparatus. 
     2. Description of the Prior Art 
     Heretofore, reciprocating compressors were generally used in freezing units such as refrigerators or ice making machines. Recently, however, the use of rotary compressors has also been suggested as a way to save space in such devices. 
     It is generally known that, in a rotary compressor, the inside of the shell thereof is maintained at a relatively high pressure, so that the lubricating oil is charged at the high pressure side, and that, when the compressor is at a standstill, the refrigerant is mixed into the compressor oil. When the compressor is started with the refrigerant thus mixed into the oil, the refrigerant remains in the oil since the pressure in the oil chamber of the compressor is not lowered contrary to conventional reciprocating compressors. The result is that a shortage in the amount of refrigerant circulated through the refrigerant system occurs and increases in pressure at the high pressure side are not achieved smoothly. The effect of the shortage of refrigerant is more pronounced in a compressor charged with only a limited amount of refrigerant. Thus, since it is difficult to increase the pressure at the high pressure side in this manner, the pressure at the low pressure side becomes extremely low and a vacuum running phenomenon occurs in which the amount of the refrigerant in circulation is significantly reduced. 
     One of the reasons why the pressure increase at the high pressure side of the compressor is retarded is that the compressor at ambient temperature acts to cool the refrigerant due to its large thermal capacity and because heat radiation from the shell surface is also considerable due to the fact that the higher pressure side is in the compressor shell. 
     As a result of the above described phenomenon, the cooling properties at the beginning of the compressor starting operation will be lowered especially at lower ambient temperatures. This causes a refrigerating or ice making operation to be continued for an extended time, so that energy loss is correspondingly increased. For example, when the ice making machine performs the ice making operation in the above-described condition, the shape of the ice product(s) formed on the freezing mold at the inlet side of the evaporator may differ considerably from that of the ice products at the outlet side of the evaporator. The reason for this is that the pressure at the low pressure side becomes unusually low from the time the ice starts, the temperature at the inlet of the evaporator or the vaporization temperature being extremely low, and the temperature at the outlet side not being significantly lowered, thus resulting in an undesirable temperature balance between the inlet and the outlet of the evaporator. 
     The above-described phenomenon will become more pronounced when a lower ambient temperature prevails about the ice making machine. However, the same phenomenon occurs from time to time at a room temperature of about 10° C., which temperature is in excess of the sensing temperature (4° C. to 8° C.) of the defrosting or harvesting completion sensor thermostat so far used as means for sensing the completion of the harvesting cycle. The above-described problem, due to the undesirable temperature balance, cannot be solved even when the harvesting cycle start is controlled by a conventional control system. That is, when the harvesting thermostat is set to a higher temperature, the harvesting operation is protracted even during normal operation thus causing a loss in time. On the other hand, the pressure at the low pressure side during harvesting may be occasionally increased to an unusual value so that problems with respect to the durability of the compressor occur. 
     An advantageous feature of the rotary compressor is that it is lighter and more compact than a reciprocating compressor. However, its small thermal capacity resulting from its lightness proves to be a disadvantage when employed in an ice making machine using hot gas for defrosting. More specifically, during the defrosting cycle of the ice making machine, the ice formed by an evaporator is detached from the freezing mold by heating. During this defrosting cycle, the refrigerant gas is condensed and turned into a refrigerant liquid which is sucked in a large quantity into the compressor resulting in the cooling of the compressor. The rotary compressor having a smaller thermal capacity than the conventional reciprocating compressor is cooled more quickly than the reciprocating compressor. This indicates that the rotary compressor has an extremely low hot gas effectiveness as compared to the reciprocating compressor thus markedly affecting the defrosting ability at the lower temperature of the rotary compressor. 
     SUMMARY OF THE INVENTION 
     It is a principal object of the present invention to provide a freezing apparatus free of the aforementioned deficiencies of the prior-art apparatus. 
     It is another object of the present invention to provide a freezing apparatus exhibiting an improved cooling performance at the initial stage of the freezing operation. 
     It is a further object of the present invention to provide an ice making machine wherein the shape of the ice products is not markedly different at the inlet and outlet sides of the evaporator at the initial ice making cycle at lower temperatures, and wherein the initial ice making cycle may be terminated within a reasonably shorter time interval to thus improve the energy efficiency thereof. 
     According to the present invention, there is provided a freezing apparatus comprising a closed loop freezing circuit including a compressor having a refrigerant outlet and a refrigerant inlet, said closed loop circuit also including a condenser, expansion means and an evaporator disposed sequentially from said refrigerant outlet towards said refrigerant inlet, and a bypass conduit having one end connected to said closed loop circuit between the outlet side of said compressor and the inlet side of said condenser and having the other end connected to said closed loop circuit between the outlet side of said expansion means and the inlet side of said evaporator, said bypass conduit including first valve means, characterized in that the freezing apparatus further comprises a sensor for sensing the temperature or the pressure of the refrigerant in said closed loop circuit, and control means connected to said sensor to control the opening and closing of said first valve means in said bypass conduit in such a manner that, when the temperature or the pressure sensed by the sensor is below a prescribed value, the cooling operation of the freezing apparatus is effected only after the first valve means in said bypass conduit is opened and the compressor is actuated for elevating its temperature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the course of the following detailed description, reference will be made to the attached drawings in which the same reference numerals denote the same or similar parts in the several figures and in which: 
     FIG. 1 is a diagrammatic view showing a freezing circuit of the freezing apparatus according to a first embodiment of the present invention; 
     FIG. 2 is a connection diagram of the freezing circuit shown in FIG. 1; 
     FIG. 3 is a diagrammatic view showing a freezing circuit of the freezing apparatus according to a third embodiment; and 
     FIG. 4 is a diagrammatic view showing a freezing circuit of the freezing apparatus according to a fourth embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, and more particularly to FIG. 1, there is shown a freezing circuit according to a preferred embodiment of a freezing apparatus using a well-known rotary compressor, and FIG. 2 shows its control circuit. The numeral 1 denotes the rotary compressor having an insulating layer 1a on its outer surface. The compressor 1 has its outlet side 1b connected through a first pipe section 2 to a condenser 3 associated with a cooling fan 4 while the condenser 3 is connected through a capillary 5 and an evaporator 6 to an inlet side 1C of the compressor 1 by way of a second pipe section 7. If necessary, a well-known accumulator, not shown, may be provided at the inlet side of the compressor 1. The compressor 1, condenser 3, capillary 5 and the evaporator 6 are connected in sequentially in this order to comprise a closed loop circuit through which the freezing medium or refrigerant circulates, via the first and second pipe sections 2 and 7, in a direction of freezing medium flow through these sections. 
     A hot gas conduit 12 having a hot gas valve 11 has one end connected to a junction 10 provided in the first pipe section 2 between the output side 1b of the compressor 1 and the inlet side of the condenser 3. The hot gas conduit 12 has its other end connected to the second pipe section 7 between the output side of the capillary 5 and the inlet side of the evaporator 6. This hot gas conduit 12 comprises a bypass circuit 13 for supplying the freezing medium exiting from the compressor 1 directly to the evaporator 6. 
     A well-known type sensor 8 is provided in the first high pressure pipe section 2 upstream of the junction 10 with respect to the direction of the flow of the freezing medium and in the vicinity of the outlet side 1b, and the sensor 8 is connected to a switch 9 that may be a thermostat, an electronic temperature switch or a pressure switch. This sensor 8 senses the temperature or the pressure of the gaseous freezing medium and the switch 9 is actuated depending upon the sensed value of the temperature or pressure for controlling the hot gas valve 11, as described later. 
     The switch 9 is provided in a control circuit 14 shown in FIG. 2 and has first and second contacts 9a and 9b. The first contact 9a of the switch 9 is connected to a well-known type controller 15 for an ice making machine, and is also connected to a normally open contact 15a and a normally closed contact 15b, both being controlled by the controller 15. The contact 15a is serially connected to the hot gas valve 11, while the contact 15b is serially connected to the cooling fan 4. The second contact 9b of the switch 9 is serially connected to the hot gas valve 11 while the compressor 1 is connected to an electrical power source by way of an ice storage switch 16 sensing the quantity of ice contained in an ice stocker of the ice making machine, not shown. 
     During operation, when the ice storage switch 16 senses that the ice quantity in the ice stocker falls short of a prescribed amount, the switch 16 is turned on, so that the compressor 1 begins operating. The operation of the compressor is continued until the ice storage switch 16 is turned off. When the temperature and/or the pressure of the freezing medium as sensed by the sensor 8 associated with the switch 9 is in excess of a predetermined value, for example a temperature of 50° C. to 60° C., the second contact 9b is turned off to close the hot gas valve 11, while the first contact 9a is turned on to supply current to the controller 15 of the ice making machine, so that the usual freezing cycle is continued. However, when the temperature or the pressure sensed by the sensor 8 is lower than the preset value, the hot gas valve 11 is opened to open the first bypass circuit 13 so that the operation is switched to a bypass operation in which the hot gas is supplied from the compressor 1 to the evaporator 6 through the hot gas valve 11. 
     During this bypass operation, which is a hot gas cycle operation for the freezer and a defrosting or harvesting cycle operation for the ice making machine, the cooling fan 4 adapted to cool the condenser 3 is at a standstill. It is noted that, during the bypass operation, the compressor 1 as a whole becomes heated due to the heat from the compressor motor and due to the compression process of the freezing gas, and therefore the temperature of the compressor 1 is effectively increased, this increase being prolonged by the thermal insulation of the insulator 1a. The reason for this is that, since the hot gas valve 11 is now opened, the quantity of the cooling medium flowing through the bypass is larger than that when flowing in the capillary 5 so that the work load of the compressor 1 is also increased. 
     Hence, with the increase in the temperature of the compressor 1, the temperature or the pressure of the gaseous freezing medium is increased. When the temperature or the pressure sensed by the sensor 8 exceeds the prescribed value, the first and second contacts 9a, 9b of the switch 9 are turned on and off, respectively, for reinitiating the freezing cycle. At the time of initiation of the freezing cycle, the freezing medium is at its normal elevated pressure, so that ice having the desired shape may be produced right at the beginning of the freezing cycle. 
     Although the sensor is provided in the present embodiment at the high pressure side of the freezing circuit, a similar effect may be attained when the sensor is provided at the low pressure side for sensing the temperature or pressure of the freezing medium flowing through the circuit. 
     FIG. 3 shows a further modification of the present invention. The present modification is also similar to the embodiment shown in FIG. 1 except that a well-known three-way valve 20 is used instead of the hot gas valve 11, which is provided at the junction 10 between the first pipe section 2 and the bypass conduit 12. When one of the flow channels of the three-way valve 20 is opened for establishing communication between the outlet side 1b of the compressor 1 and the bypass conduit 12, the other flow channel is closed for interrupting communication of the gaseous refrigerant or freezing medium from the compressor 1 towards the condenser 3. In the reverse case, the other flow channel is opened. In the present embodiment, the flow of the refrigerant gas into the condenser 3, where the volume of heat radiation is at the maximum at the high pressure side of the freezing device, is inhibited during the bypass operation, the refrigerant gas being liquefied in the condenser 3 when the pressure or the temperature in the condenser 3 is lower than the saturation pressure or temperature of the refrigerant. Thus, any remnant refrigerant in a portion of the first piping section 2 downstream of the condenser 3 and the three-way valve 20 is supplied to the evaporator 6 through capillary 5, such that almost all of the refrigerant may be utilized for the bypass operation, resulting in that the time necessary for elevating the temperature of the compressor 1 is further reduced. It is therefore possible to compensate for the lesser heat volume of the compressor while avoiding situations such as those resulting in incapacitated harvesting during the normal operating cycle, the prolongation of the harvesting time with resulting over-melting of ice products, or excess energy consumption. 
     FIG. 4 shows a further modification of the present invention. The present modification differs from the embodiment shown in FIG. 1 only in that a separate valve 21 is provided in the first pipe section 2 downstream of the junction 10. The valve 21 is closed and opened when the hot gas valve 11 is opened and closed, respectively, so that the operation is similar to that of the embodiment shown in FIG. 3. 
     With the above-described freezing apparatus making use of the rotary compressor according to the present invention, the compressor is heated rapidly even when the compressor is at ambient temperature and it is only after the shell temperature is increased that the freezing apparatus performs the ice making operation. The result is that higher pressure is substantially equivalent to the pressure during the rated operation thereof, while the lower pressure is not lowered excessively at the time of initiation of the freezing operation. With an ice making machine employing the present invention, the ice formed on the freezing plate has the same shape at both the inlet side and the outlet side of the evaporator so that ice products having a uniform shape and hence, a higher commercial value, may be produced within a normal ice making time from the first freezing cycle so that energy efficiency is improved. With a refrigerator, air conditioner or a vehicle air conditioner in which the teachings of the present invention are incorporated, the cooling effect is markedly improved due to the improved dehumidification, de-frosting or cooling at the initiation of the operation. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.