REFRIGERATION CIRCUIT

Abstract: A refrigeration circuit is disclosed, which includes a sub­ cooling control valve (12) and a decompression device (13). The sub­ cooling control valve (12) controls the flow amount of refrigerant depending upon a detected subcooling value. The decompression device (13) controls changes of the flow amount of refrigerant. Therefore, the refrigeration circuit can control the flow amount of refrigerant and prevent the occurence of hunting phenomenon.

Description: This invention relates to a refrigeration circuit for use in an automotive air conditioning system, and more particularly, to a refrigeration circuit which includes a control device for controlling the flow amount of refrigerant. Referring to Fig. 1 which shows a conventional refrigeration circuit for use in an automotive air conditioning system as disclosed e.g. in US-A-3306067 or US-A-4193781, the refrigeration circuit generally comprises a compressor 1, condenser 2, receiver drier 3, decompression device 4 and evaporator 5. Each of the components of the above refrigeration circuit is connected with each other in series and the other as mentioned above. It is well-known that a thermostatic expansion valve is utilized in the circuit as decompression device to control the flow amount and expansion of the refrigerant. The operation of expansion valve 4 is dependent on the degree of superheat at the outlet side of evaporator 5. The refrigeration circuit is usually operated within the range of superheat five through eight degrees at the outlet side of evaporator 5 to prevent reduction of efficiency of compressor 1, damage of valves of compressor 1 and the like due to liquid compression. Therefore, the heat exchange efficiency of evaporator 5 is reduced by such a degree of superheat. Further, if such a refrigeration circuit is used as automotive air conditioner, requiring a wide range of flow amount of refrigerant in this circuit, it may easily happen that liquid refrigerant is returned to the suction side of the compressor and also hunting may easily occur under lower flow amount condition. Another conventional refrigeration circuit is disclosed in Fig. 2 and the conventional refrigeration circuit includes compressor 1, condenser 2, decompression device 6, for example a capillary, an orifice or the like, evaporator 5 and accumulator 7. Each component of the refrigeration circuit is connected with each other in series and the order as mentioned above. Since accumulator 7 is connected to the outlet side of evaporator 5, the degree of superheat at the outlet side of evaporator 5 is always near zero. Therefore, the heat exchange efficiency of evaporator 5 is improved. However, within lower flow amount or middle or average flow amount of refrigerant, it may easily happen that the liquid refrigerant accumulates in accumulator 7, and it is easy for the liquid refrigerant to flow back to compressor 1. Therefore, the coefficient of performance for the refrigeration circuit is decreased. Further, under high flow amount of refrigerant, it may happen that the liquid refrigerant accumulates in condenser 2. Therefore, the radiating capacity of condenser 2 and the liquid refrigerant in accumulator 7 become insufficient. The degree of superheat at the outlet side of evaporator 5 thus increases abnormally. For retaining the sufficient volume of liquid refrigerant, accumulator 7 is thus needed to be enlarged in size. It is an object of this invention to provide a refrigeration circuit with a control device which easily controls the flow amount of refrigerant. It is another object of this invention to provide a refrigeration circuit with a control device which prevents the occurrence of hunting phenomenom. This object is achieved by means of a refrigeration circuit according to claim 1. The refrigeration circuit according to this invention includes a compressor, a condenser, an evaporator and an accumulator so that discharging refrigerant from a compressor passes through the condenser, the evaporator and the accumulator, respectively, and returns to a suction port of the compressor. A subcooling control valve is connected to the condenser and coupled to the evaporator through a fixed throttle valve so as to control a flow amount of refrigerant due to detecting a subcooling value of refrigerant at an outlet side of the condenser. The fixed throttle valve is directly connected to the subcooling control valve so as to control changes of the flow amount of refrigerant flowing into the evaporator. Further objects, features and other aspects of this invention will be understood from the following detailed description of the preferred embodiments of this invention referring to the attached drawings. Fig. 1 is a schematic drawing of a conventional refrigeration circuit; Fig. 2 is a schematic drawing of another conventional refrigeration circuit; Fig. 3 is a schematic drawing of a refrigeration circuit in accordance with one embodiment of this invention; Fig. 4 is a cross-sectional view of a flow amount control device utilized in a refrigeration circuit of Fig. 3; and Fig. 5 is a graph illustrating the relationship between the refrigerating capacity of an evaporator and the rotational speed of a compressor. Referring to the attached drawing in Fig. 3, there is shown a refrigeration circuit for use in an automotive air conditioning system in accordance with one embodiment of this invention. The refrigeration circuit of the present invention comprises compressor 10, condenser 11, subcooling control valve 12, decompression device, for example a capillary or an orifice 13, evaporator 14 and accumulator 15. The condenser 11 is connected to the outlet port of compressor 10 and also coupled to the capillary 13 through subcooling control valve 12. The evaporator 14 is connected to the capillary 13 and also coupled to the inlet port of compressor 10 through the accumulator 15. Referring to Fig. 4, the construction of a control device 21 which has the function of the subcooling control valve 12 and capillary 13 is shown. Control device 21 comprises a tubular casing 211 which includes inlet tube 212 and outlet tube 213, an operating valve 214 which is disposed in the connecting portion between inlet tube 212 and outlet tube 213, the diaphragm 215, and sensing cylinder 216. An opening 217 is formed through the inlet tube 212, and the operating valve 214 is urged so as to close the opening 217 by adjusting a spring 218. An orifice 223 is formed on the outlet tube 213. A valve seat 219, which is disposed on an upper space 221 of casing 211 and attached on one end surface of diaphragm 215, is coupled to the base of the operating valve 214 through a connecting rod 220. The diaphragm 215 divides the upper space 221 into two chambers 221a, 221b, and and one chamber 221a, in which the valve seat 219 is disposed, is in communication with the interior of inlet tube 212 through communication channel 222. The other chamber 221b communicates with the interior of the sensing cylinder 216. Refrigerant is enclosed in the sensing cylinder 216 so as to detect the temperature and to operate the diaphragm 215. The control device 21 detects the temperature of the refrigerant at the outlet side of condenser 11 by the sensing cylinder 216, i.e., the conduit between condenser 11 and control device 21 is in contact with the sensing cylinder 216. The refrigerant in the sensing cylinder 216 is changing its aspect from fluid into gas or from gas into fluid in accordance with the temperature of refrigerant at the outlet side of the condenser 11. In accordance with the change of temperature of the refrigerant, the saturation pressure of the refrigerant in the sensing cylinder 216 is thus changed. The control device 21 is operated in accordance with the counterbalance among the saturation pressure of refrigerant in the sensing cylinder 216, the pressure of the refrigerant at the outlet side of the condenser 11 and the recoil strength of the adjusting spring 218. If the control device 21 detects the subcooling value, i.e., the difference between the actual temperature of refrigerant and the saturation temperature at the same pressure of refrigerant at the outlet side of the condenser 11 is less than the predetermined subcooling value, which is determined by adjusting spring 218, i.e., the amount of the saturation pressure in the sensing cylinder 216 and the recoil strength of the adjusting spring 218 is less than the pressure of refrigerant at the outlet side of condenser 11, the operating valve 214 is urged upwardly, and the opening 217 of inlet tube 212 is opened. Thereafter, since the amount of refrigerant at the outlet side of the condenser 11 is increased, the temperature of refrigerant is thus gradually increased. At the same time, the saturation pressure of refrigerant in the sensing cylinder 126 is gradually raised together with the increase of the temperature of refrigerant at the outlet side of condenser 11, and the diaphragm 215 operates so as to close the opening 217 of inlet tube 212 against the recoil strength of adjusting spring 218. The operating valve 214 adjusts the area of opening 217 up to a position where the amount of the saturation pressure in sensing cylinder 216 and the recoil strength of adjusting spring 218 is equal to the pressure of refrigerant at the outlet side of condenser 11. The orifice 213 controls changes of the flow amount of refrigerant which flows into the evaporator 14. Referring to Fig. 5, the relationship between the refrigerating capacity of an evaporator and the rotational speed of a compressor is shown. A dotted curve shows the refrigerating capacity with respect to the refrigeration circuit which includes an expansion valve as shown in Fig. 1. A lined and dotted curve shows the refrigerating capacity with respect to the refrigeration circuit which includes a capillary as shown in Fig. 2. A solid curve shows the refrigerating capacity with respect to the refrigeration circuit in accordance with one embodiment of this invention as shown in Fig. 3. Within the low range of rotational speed of a compressor, the refrigeration circuit according to one embodiment of this invention has higher refrigerating capacity than the conventional refrigeration circuit including a capillary and almost equal refrigerating capacity to the refrigeration circuit including an expansion valve. Within the high range of rotational speed of a compressor, the refrigeration circuit according to one embodiment of this invention has the suitable refrigerating capacity which is positioned between the refrigerating capacities in accordance with the conventional refrigeration circuit including an expansion valve or a capillary. As a modification of control device 21 as shown in Fig. 4, another control device may be used which operates in accordance with detecting signals sent from sensors sensing the pressure and temperature of refrigerant at the outlet side of condenser 11 in the refrigeration circuit. Furthermore, the diaphragm 215 may be replaced by a bellows, and also orifice 223 may be replaced by a capillary as a fixed throttle valve mechanism having the same function.

Claims: Refrigeration circuit including a compressor (10), a condenser (11), an evaporator (14) and an accumulator (15) so that a discharging refrigerant from the compressor (10) passes through said condenser (11), said evaporator (14) and said accumulator (15), respectively, and returns to a suction port of said compressor (10), characterized by a subcooling control valve means (12) disposed on an outlet side of said condenser (11) to control the flow amount of refrigerant due to detecting a subcooling value of refrigerant at the outlet side of said condenser (11); and a fixed throttle valve means directly connected to said subcooling control valve such that the subcooling control valve is coupled to the evaporator through the fixed throttle valve. Refrigeration circuit in accordance with claim 1, characterized in that said subcooling control valve means (12) is integrally formed with said fixed throttle valve means. Refrigeration circuit in accordance with claim 1, characterized in that said subcooling control valve means operates in accordance with electrical signals from a detecting sensor which detects pressure and temperature of refrigerant at the outlet side of said condenser (11).

Inventors: MOTOHARU, SATO
Applicants: SANDEN CORPORATION
Application year: 1987
Main classification: F25B41
IPC codes: F25B41