US20060048524A1

US20060048524A1 - Refrigeration unit

Info

Publication number: US20060048524A1
Application number: US11/219,669
Authority: US
Inventors: Shunji Komatsu
Original assignee: Sanden Corp
Current assignee: Sanden Corp
Priority date: 2004-09-09
Filing date: 2005-09-07
Publication date: 2006-03-09
Also published as: JP2006078090A

Abstract

A refrigeration unit applied, for example, to an air conditioning system for a car has a condenser, an expansion valve, and an evaporator interposed in a refrigerant circulation passage in the order named. The circulation passage includes a fluid-flowing area for a liquid refrigerant from the condenser to the expansion valve, and a gas-flowing area mainly for a gaseous refrigerant from the evaporator to the compressor. The refrigeration unit is provided with a detector for detecting the presence of the gaseous refrigerant in the liquid-flowing area. If the detector detects the gaseous refrigerant, a warning light indicative of a refrigerant leak is turned on.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a refrigeration circuit, and more specifically to a refrigeration circuit for an air conditioning system for a vehicle, which is suitable for use of a flammable refrigerant with low global warming potential.
2. Description of the Related Art
In late years, the development of an environment-friendly air conditioning system has been advanced. This air conditioning system has a refrigeration circuit employing a refrigerant with low global warming potential. To be specific, refrigerants of this type include new alternatives for chlorofluorocarbon, such as R-152a, and HC gases, such as propane.
Because of flammability of these gases, an air conditioning system of this type, especially a vehicle air conditioning system, is provided with a gas sensor for detecting a leaked refrigerant in order to assure the safety as disclosed, for example, in Unexamined Japanese Patent Publication No. 9-104221.
When the gas sensor is used, however, even in the event of a refrigerant leak, it is impossible to detect the leak unless the gas density increases in the vicinity of the gas sensor. For this reason, there is the possibility that the sensor could not detect the refrigerant leak.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a refrigeration unit capable of detecting a refrigerant leak without fail and warning the user, the supervisor or the like.
In order to accomplish the above object, the refrigeration unit of the present invention includes a condenser, an expansion valve, and an evaporator interposed in a refrigerant circulation passage in the order named, the passage having a liquid-flowing area for a liquid refrigerant from the condenser to the expansion valve, and a gas-flowing area mainly for a gaseous refrigerant from the evaporator to the compressor; detecting means for detecting presence of the gaseous refrigerant in the liquid-flowing area, said detecting means including a detector disposed in the liquid-flowing; and warning means for outputting a detection result when the detecting means detects the gaseous refrigerant. To be concrete, for the detector, it is preferable to utilize a self-heating type thermistor, a pair of a light-emitting device and a light-receiving device or a microphone. The warning means preferably includes a warning light or buzzer.
If a refrigerant leaked out from some place of the refrigerant circulation passage, a refrigerant amount in the refrigerant circulation passage decreases, which produces a gaseous refrigerant in the liquid-flowing area of the refrigerant circulation passage through which the liquid refrigerant is supposed to flow. Therefore, the presence of the gaseous refrigerant in the liquid-flowing area is an index signifying an occurrence of a refrigerant leak. Accordingly, in the refrigeration unit of the present invention, the detecting means determines that there occurs a refrigerant leak in the refrigerant circulation passage when a gaseous refrigerant is present in the liquid-flowing area of the refrigerant circulation passage, and the presence of the gaseous refrigerant is detected by the detector. In this manner, the detecting means reliably detects the refrigerant leak by detecting the leak on the basis of the presence of the gaseous refrigerant in the liquid-flowing area. Based on the detection result given by the detecting means, the warning means warns the user, supervisor or the like of the refrigeration unit of the refrigerant leak.
In a preferred embodiment, a receiver is interposed in the liquid-flowing area, and the detector is disposed downstream from the receiver. In this embodiment, in the event of a refrigerant leak, a gaseous refrigerant is produced in the liquid-flowing area located downstream from the receiver. However, if the refrigeration unit is operated in proper working order, the receiver removes the gaseous refrigerant, so that the gaseous refrigerant is never present in the liquid-flowing area located downstream from the receiver. Consequently, the detector is prevented from making a false detection of a refrigerant leak when the refrigeration unit is in normal operation.
In a preferred embodiment, the refrigerant is a flammable refrigerant, for the flammable refrigerant generally has low global warming potential and then is environment-friendly.
In a preferred embodiment, the refrigerant circulation passage runs from an engine room to a passenger compartment of a vehicle. If the refrigerant leaked, and the driver drove the vehicle without noticing the leak, there would be a possibility that the engine or the like acts as a heat source to catch fire. According to the above-described configuration, however, the driver is surely cautioned about the refrigerant leak, which assures the safety of the driver.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:
FIG. 1 is a schematic view showing a configuration of a refrigeration unit according to one embodiment applied to an air conditioning system for a car;
FIG. 2 is a sectional view of a detector located in the refrigeration unit of FIG. 1;
FIG. 3 is a Mollier diagram for explaining the emergence of a gaseous refrigerant in the event of a refrigerant leak in a liquid-flowing area of a refrigerant circulation passage in the refrigeration unit of FIG. 1;
FIG. 4 is a graph showing relation between temperature and electric resistance in a thermistor of FIG. 2;
FIG. 5 is a view showing a modification example of the detector of FIG. 2; and
FIG. 6 is a view showing another modification example of the detector of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 is a schematic view showing a configuration of a refrigeration unit according to one embodiment applied to an air conditioning system for a car.
The refrigeration unit has a circulation passage 6 extending from an engine room 2 of a vehicle through a dash panel 3 to a passenger compartment 4, the circulation passage 6 being filled with R-152a as refrigerant. A compressor 8 is interposed in a section of the circulation passage 6 located in the engine room 2, and is activated by a driving force of an engine 10. The compressor 8 sucks the refrigerant, as a working fluid, in a phase of a low-pressure gas through a suction port thereof, compresses the sucked refrigerant therein, and then discharges the compressed refrigerant in a phase of high-temperature and high-pressure gas through a discharge port thereof. In short, the compressor 8 creates a flow of the refrigerant in the circulation passage 6 while compressing the refrigerant.
A condenser 12 is interposed in a section of the circulation passage 6 downstream of the compressor 8 in the flowing direction of the refrigerant. The condenser 12 has an outer surface which receives air from the front of the vehicle and from a propeller fan (not shown), to thereby air-cool and condense the refrigerant flowing in the inside thereof.
A receiver 14 is also interposed in a section of the circulation passage 6 downstream of the condenser 12. The receiver 14 separates an undesired gaseous refrigerant remaining in the high-pressure liquid refrigerant that has flowed in from the condenser 12, and causes only the liquid refrigerant to flow out downstream.
An expansion valve 16 and an evaporator 18 each are interposed in a section of the circulation passage 6 in the order named, downstream of the receiver 14. The evaporator 18 is disposed in the passenger compartment 4. Specifically, an air conditioning unit housing (not shown) is disposed in an instrument panel 20 located in a front section of the passenger compartment 4. The air conditioning unit housing accommodates the evaporator 18, a heater core, and a blower fan (not shown) together, which construct the air conditioning unit of the air conditioning system. The high-pressure liquid refrigerant from the receiver 14 is supplied through the expansion valve 16 to the evaporator 18, and is evaporated in the evaporator 18 to become a low-temperature and low-pressure gaseous refrigerant. The downstream side of the evaporator 18 is connected to the compressor 8, so that the gaseous refrigerant is sucked into the compressor 8. As to the expansion valve 16, the valve opening thereof is automatically varied according to a degree of superheat of the refrigerant at the downstream side of the evaporator 18, thereby adjusting the degree of superheat into a predetermined range.
In the circulation passage 6, the compressor 8, the condenser 12, the receiver 14, the expansion valve 16 and the evaporator 18 are connected to each other by conduits 22.
The refrigeration unit has a self-heating type thermistor 26 as a detector 24 for detecting a refrigerant leak in the circulation passage 6. The thermistor 26 is liquid-tightly fixed to the conduit 22 connecting the receiver 14 and the expansion valve 16. A self-heating resistance portion of the thermistor 26 projects into the conduit 22. The thermistor 26 is electrically connected to a control circuit 28 located in the instrument panel 20. The control circuit 28 supplies electric power to the thermistor 26 to cause the self-heating resistance portion of the thermistor 26 to generate heat at a prescribed heating value, and is capable of detecting electric resistance of the self-heating resistance portion of the thermistor 26.
The control circuit 28 is also electrically connected to a warning light 30 provided to the instrument panel 20. When the electric resistance of the thermistor 26 is reduced to be lower than a prescribed lower limit, the control circuit 28 carries electricity to the warning light 30, thereby turning on the warning light 30.
According to the air conditioning system for the vehicle thus configured, the passenger compartment 4 is air-conditioned by circulating the refrigerant through the circulation passage 6 during the normal air-conditioning operation of the system. To be more specific, the compressor 8, when being activated upon receiving the driving force from the engine 10, sucks the low-temperature and low-pressure gaseous refrigerant from a return path of the circulation passage 6, compresses the sucked gaseous refrigerant, and discharges the compressed gaseous refrigerant to a feed path of the circulation passage 6. The discharged refrigerant passes the condenser 12 with the condensation from the phase of high-temperature and high-pressure gas to the liquid phase. The refrigerant in the liquid phase passes through the receiver 14 to the expansion valve 16. The expansion valve 16 makes the refrigerant jet into the evaporator 18 with the expansion of the refrigerant from the liquid phase to the gas-liquid mixing phase of low-temperature and low-pressure and evaporate in the evaporator 18 while the valve opening thereof varies so that the degree of superheat of the refrigerant at the outlet of the evaporator 18 falls within a given range. The refrigerant evaporated in the evaporator 18 is again sucked into the compressor 8.
In this circulation process of the refrigerant, once the blower fan of the air conditioning unit is activated, cold air from which evaporation heat has been removed by passing through the evaporator 18 is fed into the passenger compartment 4. This cold air air-conditions the passenger compartment 4 at a desired preset temperature.
The air conditioning system for the vehicle thus configured employs R-152a with low global warming potential as refrigerant, thereby being environment-friendly.
According to the air conditioning system for the vehicle thus configured, even if the refrigerant leaked out from some place of the circulation passage 6, the warning light 30 is turned on to reliably warn the driver, as an operator, of the refrigerant leak. Therefore, if by any chance the R-152a that is a flammable refrigerant leaked out of the circulation passage 6, the driver certainly notices the refrigerant leak, thereby coping with the leak. Consequently, it is possible to surely avoid the accident in which the engine 10 or the like acts as a heat source to catch fire, and the safety of the driver is assured.
More specifically, in the normal circulation process of the refrigerant, a portion of the circulation passage 6 which is located between the condenser 12 and the expansion valve 18 forms a liquid-flowing area through which the high-pressure liquid refrigerant flows. The state of the refrigerant running through the liquid-flowing area is indicated by dot A in the Mollier diagram shown by a chain double-dashed line of FIG. 3. Dot A is located within the supercooled liquid area that stretches leftwards from a saturated liquid line. A portion of the circulation passage 6 which is located between the evaporator 18 and the compressor 8 forms a gas-flowing area through which the low-pressure gaseous refrigerant flows.
Contrarily, if the refrigerant leaked out from some place of the circulation passage 6, and a refrigerant amount within the circulation passage 6 decreased, the refrigerant pressure lowers in the liquid-flowing area and yet rises in the gas-flowing area. A Mollier diagram showing this condition is indicated by a solid line of FIG. 3. The state of the refrigerant running through the liquid-flowing area is shown by dot B on the Mollier diagram. Dot B is located within a gas-liquid mixing phase area expanding between the saturated liquid line and a saturated vapor line. Thus, if the refrigerant amount within the circulation passage 6 decreased, the gaseous refrigerant gradually increases among the refrigerant flowing through the liquid-flowing area of the circulation passage 6 through which the liquid refrigerant is supposed to flow. That is to say, the presence of the gaseous refrigerant in the liquid-flowing area is an index signifying an occurrence of a refrigerant leak in the circulation passage 6.
As to the detector 24 fixed to the liquid-flowing area of the circulation passage 6, namely the self-heating type thermistor 26, the self-heating resistance portion thereof is supplied with electric power from the control circuit 28 and generates heat at the prescribed heating value, and at the same time loses its heat to the surrounding refrigerant.
TABLE 1 below shows heat conductivity of the R-152a in liquid and gaseous phases at a temperature of 25 degrees centigrade.

TABLE 1

Phase Heat conductivity W/(m · K)

Liquid phase 0.105

Gaseous phase 0.0136
As shown in TABLE 1, the R-152a of the liquid phase has almost about ten times as great heat conductivity as the R-152a of the gaseous phase. As a result, when the refrigerant amount within the circulation passage 6 decreases, and the gaseous refrigerant starts getting mixed into the liquid-flowing area, an amount of heat taken from the self-heating resistance portion of the thermistor 26 decreases, and the temperature of the self-heating resistance portion rises. The temperature rise of the self-heating resistance portion, as diagrammatically shown in FIG. 4, causes a reduction in electric resistance of the self-heating resistance portion of the thermistor 26. In other words, a B-value and a C-value of the thermistor 26 are determined such that they satisfy an expression; (the amount of heat taken from the self-heating resistance portion by the gaseous refrigerant of a superheated gas area)<(the heating value of the self-heating resistance portion)<(the amount of heat taken from the self-heating resistance portion by the liquid refrigerant of the supercooled liquid area).
The electric resistance of the self-heating resistance portion of the thermistor 26 is measured and monitored by the control circuit 28. When the electric resistance of the self-heating resistance portion becomes smaller than the prescribed lower limit, the control circuit 28 determines that the state of the refrigerant is changed from the supercooled liquid area to the gas-liquid mixing phase area. The determination of the change into the gas-liquid mixing phase area means the determination of the presence of the gaseous refrigerant in the liquid-flowing area and of the occurrence of a refrigerant leak. Based on the determination result of the occurrence of the refrigerant leak, the control circuit 28 carries electricity to the warning light 30 to turn it on, thereby warning the driver of the refrigerant leak.
The present invention is not limited to the above-described one embodiment, and may be modified in various ways.
Although in the one embodiment, the receiver 14 is interposed between the condenser 12 and the expansion valve 16, it is possible to interpose an accumulator, instead of the receiver 14, between the evaporator 18 and the compressor 8, and to utilize an orifice with a fixed opening, in stead of the expansion valve 18. In this case, mainly the gaseous refrigerant flows through the gas-flowing area lying between the evaporator 18 and the accumulator. Occasionally, since the degree of superheat of the refrigerant at the outlet of the evaporator 18 is not controlled by the orifice, the liquid refrigerant which does not evaporate in the evaporator 18 also runs the gas-flowing area, albeit only in small amount, and is reserved in the accumulator. Meanwhile, if the gaseous refrigerant that is accidentally not condensed by the condenser 12 flows through the liquid-flowing area of the circulation passage 6, this triggers false operation of the detector 24, resulting in a deterioration of detection accuracy with respect to a refrigerant leak. It is then preferable that the detector 24 be disposed downstream of the receiver 14 as in the one embodiment.
Although the R-152a is used as refrigerant in the one embodiment, another chlorofluorocarbon (HFC gas) or HC gases, such as propane, may be used instead.
In the one embodiment, the warning light 30 that visually attracts attention is used as warning means for the driver. The warning means, however, serves satisfactorily enough as long as it causes the driver to notice a refrigerant leak clearly. Accordingly, as shown by a chain double-dashed line in FIG. 1, a warning buzzer 38 that auditorily attracts attention may be utilized instead of or together with the warning light 30.
Although in the one embodiment, the thermistor 26 is used as the detector 24 for detecting the gaseous refrigerant in the liquid-flowing area of the circulation passage 6, an optical detector 24 formed of a light-emitting device 32 and a light-receiving device 34 capable of receiving light from the light-emitting device 32 may be utilized as shown in FIG. 5. The light-emitting device 32 and the light-receiving device 34 are diametrically arranged on both sides of the conduit 22 with respective transparent glass sheets 36 interposed therebetween. The light emitted from the light-emitting device 32 passes through the glass sheets 36 and the liquid refrigerant in the conduit 22, to thereby enter the light-receiving device 34. When the light passes through the liquid refrigerant, if bubbles of the gaseous refrigerant are included in the liquid refrigerant, the light is scattered due to the bubbles, which decreases the intensity of the light incident on the light-receiving device. Therefore, the control circuit 28 detects the decrease of the intensity of the light entering the light-receiving device 34, and turns on the warning light 30 if the decrease reaches a certain or higher level.
Moreover, as shown in FIG. 6, the detector 24 may be replaced with a microphone 40. In this case, the presence of the gaseous refrigerant in the liquid refrigerant is detected by detecting abnormal noises produced when the bubbles of the gaseous refrigerant are spouted from the expansion valve 16 by means of the microphone 40.
It is noted that, in case that a pressure sensor is utilized as the detector 24, a pressure decrease in the circulation passage 6 is modest until there remains scarcely any refrigerant in the circulation passage 6, which makes it difficult to detect a refrigerant leak in early stages. As a consequence, it is preferable that the thermistor 26 be used as the detector 24 as in the one embodiment.
Needless to say, the refrigeration unit of the present invention can be applied not only to the air conditioning system for the vehicle but also to a room air conditioner, a refrigerator, and a freezer. In any case, the refrigeration unit warns the user, the supervisor or the like of a refrigerant leak without fail.
The invention thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A refrigeration unit comprising:

a condenser, an expansion valve, and an evaporator interposed in a refrigerant circulation passage in the order named, the passage having a liquid-flowing area for a liquid refrigerant from said condenser to said expansion valve, and a gas-flowing area mainly for a gaseous refrigerant from said evaporator to said compressor;

detecting means for detecting presence of the gaseous refrigerant in said liquid-flowing area, said detecting means including a detector disposed in said liquid-flowing area; and

warning means for outputting a detection result when said detecting means detects the gaseous refrigerant.

2. The refrigeration unit according to claim 1, wherein:

a receiver is interposed in said liquid-flowing area; and

said detector is disposed downstream from said receiver.

3. The refrigeration unit according to claim 2, wherein:

said detector includes a self-heating type thermistor.

4. The refrigeration unit according to claim 3, wherein:

said refrigerant is a flammable refrigerant.

5. The refrigeration unit according to claim 4, wherein:

said warning means includes a warning light.

6. The refrigeration unit according to claim 4, wherein:

said warning means includes a warning buzzer.

7. The refrigeration unit according to claim 4, wherein:

said refrigerant circulation passage runs from an engine room to a passenger compartment of a vehicle.

8. The refrigeration unit according to claim 2, wherein:

said detector includes a light-emitting device and a light-receiving device.

9. The refrigeration unit according to claim 8, wherein:

said refrigerant is a flammable refrigerant.

10. The refrigeration unit according to claim 9, wherein:

said warning means includes a warning light.

11. The refrigeration unit according to claim 9, wherein:

said warning means includes a warning buzzer.

12. The refrigeration unit according to claim 9, wherein:

13. The refrigeration unit according to claim 2, wherein:

said detector includes a microphone.

14. The refrigeration unit according to claim 13, wherein:

said refrigerant is a flammable refrigerant.

15. The refrigeration unit according to claim 14, wherein:

said warning means includes a warning light.

16. The refrigeration unit according to claim 14, wherein:

said warning means includes a warning buzzer.

17. The refrigeration unit according to claim 14, wherein: