Refrigerator

Abstract: A refrigerator (11) having a refrigerant circulating circuit (12) for circulating a mixture of a refrigerant and a refrigerating machine oil. The refrigerator (11) includes a compressor (14) with a bypass circuit (31) or a variable displacement compressor (41), a state detecting sensor (19) for sensing a phase of the refrigerant mixture, determining circuit (35) for determining whether the detected phase is in a two phase separation area, and a control unit (36) for controlling the amount of the refrigerant passing through the bypass circuit (31) or the displacement of the variable displacement compressor (41). When the refrigerant mixture enters into the two phase separation area, the amount of discharge or the displacement of the compressor (14, 41) is decreased. The temperature of refrigerant mixture is lowered accordingly and the phase changes from the two phase separation area. The refrigerating machine oil is maintained in a uniformly mixed state with the refrigerant and circulates with the refrigerant to the compressor (14, 41). As a result a lock up or breakage of the compressor (14, 41) is prevented.

Description: The present invention relates to a refrigerant circulating circuit in which a mixture of a refrigerant and a refrigerating machine oil is circulated. A typical conventional refrigerator air for vehicles is shown in FIG. 6. A refrigerant such as freon gas is circulated in refrigerant circulating circuit 1 formed from pipe 2. Compressor 3, condenser 4, receiver dryer 5, expansion valve 6 and evaporator 7 are provided in circulating circuit 1 sequentially in the direction of circulation of the refrigerant, shown by arrows. The endothermic surface of evaporator 5 is exposed to the interior of the vehicle (not shown). After the refrigerant is compressed by compressor 3, the refrigerant is transformed in phase from a high-pressure gas to a high-pressure liquid in condenser 4 and further to a low-pressure gas as it passes through expansion valve 6 and evaporator 7. When the refrigerant is transformed from a liquid phase to a gaseous phase (vapor phase) by evaporator 7, the refrigerant absorbs heat from the interior of the vehicle and the vehicle interior is cooled. In such a refrigerator, a mixture of a refrigerant and a refrigerating machine oil is usually used as the refrigerant circulated in the circulating circuit 1. The refrigerating machine oil lubricates the slidable portions of compressor 3. Although freon has been mainly used as the refrigerant for such a refrigerator, recently substitute refrigerants for freon have been used. Among refrigerating machine oils used for such substitute refrigerants, there are some oils which cannot sufficiently dissolve in the refrigerants. In such a case, the compatibility between the refrigerant and the refrigerating machine oil depends on temperature. Namely, if the temperature of a mixture of a refrigerant and a refrigerating machine oil is high, the refrigerant and the refrigerating machine oil are separated to a two phase mixture. As the result of such a two phase separation, a part of the refrigerating machine oil stagnates in some portions in circulating circuit 1, and an insufficient amount of the refrigerating machine oil is returned to compressor 3. Consequently, there is a possibility that compressor 3 may lock up or break. Accordingly, it would be desirable to provide a refrigerant circuit which can prevent a two phase separation in a mixture of a refrigerant and a refrigerating machine oil circulated in a refrigerant circulating circuit, thereby preventing a compressor from locking up or breaking. US-A-4167858 discloses a refrigerant circulating circuit for circulating a mixture of a refrigerant and a refrigerating machine oil, the circulating circuit comprising compressor means for compressing the mixture; a condenser coupled to the output of the compressor means; an expansion valve coupled to an output of the condenser; an evaporator coupled to an output of the condenser and to an input of the compressor means; state detecting means, coupled between the condenser and the expansion valve, for detecting a phase of the mixture in the circulating circuit and outputting a detection signal related to the detected phase; and determining means, coupled to the state detecting means, for determining whether the detection signal is greater or less than a reference value, which is such as to represent a boundary value between a two phase separation area of the mixture in which part of the refrigerating machine oil is separated from the refrigerant, and a normal area in which the refrigerating machine oil is mixed with the refrigerant, and outputting a determination signal related to the determination; and according to the present invention, such a circuit is characterised by control means, coupled between the determining means and the compressor means, for reducing the displacement of the compressor means when the determining means detects the two phase separation area. As the result of the reduction of the displacement of the compressor device, the amount of the mixture circulated in the circulating circuit decreases, and the temperature of the circulated mixture is lowered. The circulated mixture can get out from two phase separation area caused depending upon the temperature of the mixture. The temperature of the mixture is controlled at a sufficiently low temperature, and the refrigerating machine oil can sufficiently dissolve in the refrigerant. A sufficient amount of the refrigerating machine oil is circulated and returned to the compressor together with the refrigerant, and a lock up or a breakage of the compressor can be prevented. FIG. 1 is a schematic view of a refrigerator according to a first embodiment of the present invention. FIG. 2 is an enlarged sectional view of a photoelectric refrigerant state detecting device of the refrigerator shown in FIG. 1. FIG. 3 is a graph showing the relationship between amount of circulated refrigerant and temperature of the refrigerant in a high-pressure side of a circulating circuit. FIG. 4 is a graph showing the relationship between temperature of circulated refrigerant and amount of bypassed refrigerant in the refrigerator shown in FIG. 1. FIG. 5 is a schematic view of a refrigerator according to a second embodiment of the present invention. FIG. 6 is a schematic view of a prior art refrigerator. Referring to the drawings, FIGS. 1 and 2 illustrate a refrigerator according to a first embodiment of the present invention. In FIG. 1, refrigerator 11 has refrigerant circulating circuit 12 formed from pipe 13. Compressor 14, condenser 15, receiver dryer 16, expansion valve 17 and evaporator 18 are provided in circulating circuit 11 sequentially in the direction of circulation of the refrigerant which is shown by arrows. Compressor 14 is driven by, for example, an engine of a vehicle (not shown). A mixture of a refrigerant and a refrigerating machine oil (hereinafter, referred to as "refrigerant mixture") is circulated in circulating circuit 11. FIG. 2 illustrates a flow sensor 19 provided on pipe 13 as a refrigerant state detecting device. Flow sensor 19 comprises a photoelectric sensor. Flow sensor 19 includes emitter 20 emitting a light towards the interior of pipe 13 constructed from, for example, a photodiode, and receiver 21 for receiving the light transmitted through the pipe (and refrigerant mixture in the pipe) constructed from, for example, a phototransistor. Sensor 19 is attached to pipe 13 so that emitter 20 and receiver 21 are aligned with each other. O-rings 24 and 25 are interposed between sensor 19 and pipe 13 for sealing therebetween. The light emitted from emitter 20 is sent through sight glass 22 into the interior of pipe 13. The light transmitted through the pipe is received by receiver 21 through sight glass 23. Flow sensor 19 detects transmittance of the light transmitted by emitter 20 and received by receiver 21. The transmittance of the light transmitted through pipe 13 indicates a phase state of refrigerant mixture. If the refrigerating machine oil is sufficiently mixed with and dissolved in the refrigerant, the amount of light transmitted through the refrigerant mixture is relatively large. If the refrigerating machine oil is insufficiently mixed with and dissolved in the refrigerant, i.e., the refrigerating machine oil and the refrigerant are in two phase separation state, the refrigerant mixture becomes translucent and the amount of light transmitted through the mixture refrigerant is relatively small. Therefore, flow sensor 19 can detect a phase state of the refrigerant mixture circulating in a high-pressure side of circulating circuit 12. In FIG. 1, a bypass circuit 31 is provided on circulating circuit 12 in this embodiment. Bypass circuit 31 comprises pipe 32 coupled to an input and an output of compressor 14 and solenoid valve 33 provided on the pipe. Solenoid valve 33 controls the amount of refrigerant mixture passing through bypass circuit 31 by control of on-off ratio thereof. Flow sensor 19 is coupled to amplifier 34 for amplifying a signal sent from the flow sensor. Amplifier 34 is coupled to comparator 35 provided as a device for comparing a signal sent from the amplifier with a predetermined reference value, determining whether the signal is greater or less than the reference value and outputting a determination signal to control unit 36. Control unit 36 is coupled to comparator 35 and solenoid valve 33. Control unit 36 outputs a signal to solenoid valve 33 for controlling the operation of the solenoid valve in accordance with the signal sent from comparator 35. In the refrigerator, a phase of the refrigerant mixture is detected by flow sensor 19. After the detection signal is amplified by amplifier 34, the detection signal is compared with the reference value in comparator 35. The reference value is preset as a boundary value between a two phase separation area of the refrigerant mixture in which a part of the refrigerating machine oil is separated from the refrigerant and a normal area in which the refrigerating machine oil is uniformly mixed and dissolved in the refrigerant. If the detection signal is less than the reference value, then the refrigerant mixture is in a two phase separation state, and comparator 35 outputs a determination signal indicating two phase separation to control unit 36. Control unit 36 outputs a signal for operation of solenoid valve 33 in accordance with the determination signal sent from comparator 35. Solenoid valve 33 is operated to be opened by the signal of control unit 36. The refrigerant mixture flows through bypass circuit 31 as well as through compressor 14. Consequently, the displacement of compressor 14 decreases by the flow through bypass circuit 31. The amount of the refrigerant mixture circulated in a high-pressure side of circulating circuit 12 decreases, and the temperature of the circulated refrigerant mixture is lowered accordingly. In the operation of solenoid valve 33, the on-off ratio of the solenoid valve may be controlled. Namely, the on-off ratio is increased when the determination signal indicating two phase separation is output from comparator 35. FIG. 3 illustrates a relationship between amount of circulated refrigerant mixture and temperature of the refrigerant mixture in a high-pressure side of circulating circuit 12. As the amount of circulated refrigerant mixture increases, the temperature of the refrigerant mixture increases. Point "B" is in a normal area, point "C" is in a two phase separation area and point "A" is on a boundary between the normal area and the two phase separation area. If the temperature of the refrigerant mixture enters into the two phase separation area such as point "C", the refrigerant mixture becomes translucent. The phase of the refrigerant mixture is detected by flow sensor 19, the detection signal is output to comparator 35, and the determination signal of two phase separation is output to control unit 36. Solenoid valve 33 is operated to open bypass circuit 31 or increase the amount of refrigerant mixture passing through the bypass circuit by the operation signal output from control unit 36. Since the amount of the refrigerant mixture circulated by compressor 14 decreases by the bypass flow, the temperature of the circulated refrigerant mixture lowers below the boundary such as point "B". As a result, the phase of the refrigerant mixture changes from the two phase separation area to the normal area, and a lock up or a breakage of compressor 14 can be prevented. FIG. 4 illustrates the relationship between the temperature of the refrigerant mixture circulated in circulating circuit 12 and the amount of the bypassed refrigerant mixture through bypass circuit 31. When the temperature of the refrigerant mixture has reached the boundary of the two phase separation area (point "D"), a part of the refrigerant mixture is bypassed through bypass circuit 31. As the amount of the bypassed refrigerant mixture increases, the temperature of the refrigerant mixture is lowered. Therefore, the temperature of the refrigerant mixture is controlled to stay at a desirable temperature, for example, point "E" by an appropriate control of solenoid valve 33. Although it can be determined when the refrigerant mixture enters into a two phase separation area by using a temperature sensor for sensing the temperature of the circulated refrigerant mixture, in practice it is difficult to determine because the characteristic curve indicating the relationship between amount of circulated refrigerant mixture and temperature of the refrigerant mixture, such as a curve shown in FIG. 3, varies depending upon an atmosphere temperature. In the present invention, the phase of the refrigerant mixture can be properly and accurately detected by photoelectric sensor 19. FIG. 5 illustrates a refrigerator according to a second embodiment of the present invention. In this embodiment, a variable displacement compressor 41 is used and a bypass circuit is not necessary. An actuator 42 is attached to compressor 41 for controlling the displacement of the compressor. The operation of actuator 42 is controlled in accordance with a signal sent from control unit 36. Other parts of the refrigerator are substantially the same as in the first embodiment shown in FIGS. 1 and 2. In such a structure, the displacement of compressor 41 is appropriately decreased when flow sensor 19 detects that the refrigerant mixture enters into a two phase separation area. The temperature of the refrigerant mixture is lowered by the reduction of the displacement, and the two phase separation state can be dissolved. Although flow sensor 19 is disposed on pipe 13 at a position between receiver dryer 16 and expansion valve 17, the flow sensor may be disposed in or on the receiver dryer.

Claims: A refrigerant circulating circuit (12) for circulating a mixture of a refrigerant and a refrigerating machine oil, the circulating circuit (12) comprising compressor means (14,41) for compressing the mixture; a condenser (15) coupled to the output of the compressor means (14,41); an expansion valve (17) coupled to an output of the condenser (15); an evaporator (18) coupled to an output of the condenser (15) and to an input of the compressor means (14,41); state detecting means (19), coupled between the condenser (15) and the expansion valve (17), for detecting a phase of the mixture in the circulating circuit (12) and outputting a detection signal related to the detected phase; and determining means (35), coupled to the state detecting means (19), for determining whether the detection signal is greater or less than a reference value, which is such as to represent a boundary value between a two phase separation area of the mixture in which part of the refrigerating machine oil is separated from the refrigerant, and a normal area in which the refrigerating machine oil is mixed with the refrigerant, and outputting a determination signal related to the determination; characterised by control means (36), coupled between the determining means (35) and the compressor means (14,41), for reducing the displacement of the compressor means (14,41) when the detecting means detects the two phase separation area. A refrigerant circulating circuit (12) according to claim 1, wherein the state detecting means (19) comprises a sensor for sensing a transmittance of light of the mixture, and the control means (36) controls the displacement of the compressor means (14,41) to decrease when the detection signal is less than the reference value. A refrigerant circulating circuit (12) according to claim 2, wherein the sensor (19) comprises an emitter (20) for emitting light and a receiving (21) for receiving light transmitted through the mixture. A refrigerant circulating circuit (12) according to any one of the preceding claims, further comprising a receiver dryer (16) provided between the condenser (15) and the expansion valve (17). A refrigerant circulating circuit (12) according to claim 4, wherein the state detecting means (19) is disposed between the receiver dryer (16) and the expansion valve (17). A refrigerant circulating circuit (12) according to claim 4, wherein the state detecting means (19) is disposed on the receiver dryer (16). A refrigerant circulating circuit (12) according to any one of claims 1 to 6, wherein the compressor means (41) comprises a variable displacement compressor. A refrigerant circulating circuit (21) according to claim 7, wherein the control means (36) includes an actuator (42) provided for controlling the displacement of the variable displacement compressor (41). A refrigerant circulating circuit (12) according to any one of the claims 1-6, wherein the compressor means comprises a compressor (14), a bypass circuit (31) coupled between an input and an output of the compressor (14) for bypassing an amount of the mixture in the circulating circuit (12) and means (33) for controlling the amount of bypassed mixture in accordance with the determination of the determining means (35). A refrigerant circulating circuit (12) according to claim 9, wherein the bypass amount control means (33) comprises a solenoid valve.

Inventors: KOBAYASHI KAZUMITSU, KOMATSU SYUNJI, KURIBARA MASARU, NAKAJIMA YUJI, KOBAYASHI, KAZUMITSU, KOMATSU, SYUNJI, KURIBARA, MASARU, NAKAJIMA, YUJI
Applicants: JAPAN ELECTRONIC CONTROL SYST, SANDEN CORP, JAPAN ELECTRONIC CONTROL SYSTEMS COMPANY, LTD., SANDEN CORPORATION
Application year: 1991
Main classification: F25B49
IPC codes: F25B41, F25B1, F25B49