KR100539594B1 - Cooling apparatus - Google Patents

Abstract

The present invention relates to a cooling apparatus which improves the operation efficiency of the compressor and efficiently performs the cooling operation by reliably preventing the damage caused by the backflow of the compressor and the sliding of the sliding portion due to the melting of the refrigerant into the lubricating oil. The cooling device 1 of the present invention has a temperature sensor (oil temperature detection means) 9 in which an oil temperature control device 12 for controlling the temperature of the lubricating oil in the bottom of the compressor 2 detects the temperature of the lubricating oil in the bottom of the compressor 2. ), A pressure sensor (suction pressure detecting means) 10 for detecting the suction pressure of the compressor 2, and an oil temperature control range of the lubricating oil temperature in the bottom of the compressor 2 according to the output signal of the pressure sensor 10 is calculated. Oil temperature determination means 14, oil temperature determination means 14 for comparing the oil temperature control range calculated by the oil temperature range calculation means 13 and the output signal of the temperature sensor 9, and oil temperature determination means 14 The operation is controlled by the solenoid valve driving means (drive means) 15 which is operated in accordance with the output signal of the controller, and the oil temperature adjusting means 11 for adjusting the temperature of the lubricating oil in the compressor 2 is provided.

Description

Cooling device {COOLING APPARATUS}

The present invention relates to a cooling device that ensures compressor reliability and improves its efficiency to enable stable and efficient operation.

In a conventional cooling device in which a compressor, a condenser, a refrigerant liquid tank, an expansion valve, and a cooler are connected through piping for refrigerant circulation to configure a refrigeration cycle, the temperature of the lubricating oil in the compressor is detected and the detected temperature exceeds the first predetermined temperature. If the condenser fan is installed at the condenser fan at full speed, and if the temperature inside the freezer machine room exceeds a predetermined temperature, the condenser fan is operated along with the operation of the machine room ventilation fan to perform the arrangement in the machine room. By lowering the condensation temperature of the valve, a solenoid valve is provided in a bypass pipe communicating from the refrigerant liquid tank to the compressor suction pipe, and the solenoid valve is opened when the detected temperature exceeds the first predetermined temperature. When the refrigerant gas flows through the suction pipe of the compressor to lower the suction gas temperature of the compressor. This prevents the temperature rise of the lubricating oil in the compressor caused by the increase of the condensation temperature of the refrigerant, and when the detection temperature exceeds a predetermined upper limit value or the detection temperature is lower than a predetermined lower limit value, the compressor reverses the liquid. In the case where it is determined that a reverse flow is occurring, a refrigeration apparatus is known that improves the reliability of the compressor by stopping the compressor to prevent excessive pressure from occurring in the compressor (see Japanese Patent Laid-Open No. 10-311612). .

However, in the above-mentioned conventional refrigeration apparatus, the condenser fan or the machine room ventilation fan is controlled only by the temperature of the lubricating oil in the compressor, or the inlet of the liquid refrigerant from the refrigerant liquid tank to the compressor is controlled to adjust the condensation temperature of the refrigerant. Excessive rise and fall of lubricating oil is prevented, but refrigeration cycle control based on not only the temperature of lubricating oil in the compressor but also the suction pressure of the refrigerant sucked into the compressor is not performed. When the lubricating oil temperature rises and falls, there is a problem in that the compressor is stopped and the compressor cannot be operated with high efficiency at all times, and thus the refrigeration apparatus cannot be operated stably and efficiently.

In addition, when the low pressure vessel type compressor is used as the compressor, the lubricating oil in the compressor is diluted by dissolving the refrigerant, but since the degree of dilution cannot always be accurately suppressed, the lubricating performance of the lubricating oil is deteriorated and the sliding part of the compressor is worn. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to reliably prevent the damage caused by backflow of the compressor and the sliding of the sliding part due to the refrigerant dilution of the compressor lubricating oil, and to improve the operation efficiency of the compressor. It is an object of the present invention to provide a cooling apparatus that can be performed.

The present invention is characterized by the following points to solve the above problems.

That is, the cooling device according to claim 1 comprises a refrigeration cycle by connecting a compressor, a condenser, a decompression device, and an evaporator through a refrigerant circulation pipe, and a cooling device provided with an oil temperature control device for controlling the lubricating oil temperature in the bottom of the compressor. The oil temperature control apparatus includes oil temperature detecting means for detecting a lubricating oil temperature in the compressor bottom, suction pressure detecting means for detecting suction pressure of the compressor, and an output signal of the suction pressure detecting means. Oil temperature range calculating means for calculating the oil temperature control range of the lubricating oil temperature, oil temperature determining means for comparing the oil temperature control range calculated by the oil temperature range calculating means and the output signal of the oil temperature detecting means, and the output signal of the oil temperature determining means Control the operation by the drive means operated according to the control of the temperature of the lubricant in the compressor Is characterized by including an oil temperature adjusting means.

In such a cooling device, when the lubricating oil temperature in the bottom of the compressor is detected by the oil temperature detecting means and the suction pressure of the refrigerant sucked into the compressor is detected by the suction pressure detecting means, the oil temperature range is calculated according to the detected suction pressure. The means calculates the temperature range at which the lubricating oil temperature in the compressor bottom should be controlled. When the oil temperature determining means compares the temperature range of the lubricating oil to be controlled with the temperature of the lubricating oil detected by the temperature detecting means, the driving means operates to control the operation of the oil temperature adjusting means according to the comparison result. According to the operation of the oil temperature adjusting means, the lubricating oil in the compressor can be cooled in a timely manner and the temperature thereof can be prevented from excessively rising or falling, so that it is effectively maintained in a certain range. The efficiency is improved.

The cooling device of Claim 2 is a cooling device of Claim 1, Comprising: The bypass pipe which the said oil temperature adjustment means connects the pipe which connects the said condenser and the said decompression device to the pipe which connects the said evaporator and the said compressor, And a flow rate adjusting means provided in the bypass circuit to control the opening and closing operation by the driving means to adjust the flow rate of the refrigerant flowing in the bypass circuit.

The cooling device according to claim 3 is the cooling device according to claim 2, wherein the flow rate adjusting means is made by connecting the solenoid valve and the capillary tube in series, and the opening and closing operation of the solenoid valve is controlled by the driving means. It features.

The cooling device according to claim 4 is characterized in that, in the cooling device according to claim 2, the flow rate adjusting means includes an electric expansion valve, and the electric expansion valve controls the opening degree adjustment operation by the driving means.

The cooling device according to claim 5 is the cooling device according to claim 1, wherein the oil temperature adjusting means includes a blower whose rotational motion is controlled by the driving means and blows to the outer surface of the bottom of the compressor. .

The cooling device according to claim 6 is characterized in that the oil temperature detecting means comprises a temperature sensor mounted on the surface of the container bottom of the compressor in the cooling device according to any one of claims 1 to 5.

EMBODIMENT OF THE INVENTION Hereinafter, the cooling apparatus which concerns on embodiment of this invention is demonstrated with reference to an accompanying drawing.

1 shows a cooling device 1 according to a first embodiment of the present invention. This cooling device 1 annularly pumps the compressor 2, the condenser 3, the electric expansion valve (pressure reducing device) 4, and the evaporator 5 through the refrigerant circulation pipe 6, as in the conventionally known cooling device. The refrigeration cycle is constituted by the

The compressor (2) is a conventionally well-known low-pressure vessel-type compressor in which a compressor unit and an electric motor (motor) driving the compressor unit are contained in a sealed container, and lubricating oil for lubricating the sliding part of the compressor unit is contained in the sealed container bottom.

The pipe 6b connecting the electric expansion valve 4 connected to the evaporator 5 via the pipe 6a to the condenser 3 connects the suction port of the compressor 2 and the evaporator 5 to each other. It is connected to the piping 6c to be connected via the bypass piping (bypass circuit) 7.

In the bypass pipe 7, a flow rate adjusting means 8 consisting of a solenoid valve 8a and a capillary tube 8b is positioned on the condenser 3 side (upstream side). The capillary tube 8b is placed on the compressor 2 side (downstream side). The discharge port of the compressor 2 and the condenser 3 are connected via a pipe 6d. In addition, a temperature sensor (oil temperature detection means) 9 is attached to the outer circumferential surface of the lower part of the sealed container of the compressor 2 (the part corresponding to the outer side of the lubricating oil storage part in the bottom of the compressor 2). It is installed in a state so as to indirectly detect the temperature of the lubricating oil. In addition, a pressure sensor (suction pressure detection) for detecting a suction pressure of the refrigerant of the compressor (2) in the pipe (6c1) of the connection portion of the pipe (6c) with the bypass pipe (7) and the suction port of the compressor (2). Means) 10 is provided. An oil temperature adjusting means 11 is configured by the bypass pipe 7, the solenoid valve 8a, and the capillary tube 8b.

In addition, the cooling device 1 operates the solenoid valve 8a according to the temperature of the lubricating oil detected by the temperature sensor 9 and the pressure sensor 10 and the suction pressure of the refrigerant, so that the bypass pipe 7 is operated. An oil temperature control device 12 is provided that adjusts the flow rate of the refrigerant flowing therein and controls the temperature of the lubricating oil in the bottom of the compressor 2.

The oil temperature control device 12 calculates a temperature range (oil temperature control range) to control the temperature of the lubricating oil in the bottom of the compressor 2 according to the output signals of the temperature sensor 9 and the pressure sensor 10. Oil temperature determining means 14 for comparing the oil temperature control range calculated by the oil temperature range calculating means 13 and the oil temperature range calculating means 13 with the output signal of the temperature sensor 9, and the oil temperature determining means 14 A solenoid valve driving means (drive means) 15 for controlling the opening / closing operation of the solenoid valve 8a of the flow rate adjusting means 8 in accordance with the output signal of the?

Next, the effect | action of the cooling apparatus 1 of the said structure is demonstrated with reference to FIG.

First, when the operation starts when the solenoid valve 8a is closed, the refrigerant compressed by the compressor 2 and the temperature is elevated flows to the condenser 3 through the pipe 6d and cooled in the condenser 3. After passing through the pipe (6b) to the motor-driven expansion valve (4) is expanded by the action of the motor-driven expansion valve (4), the temperature is lowered, and then flows into the evaporator (5) through the pipe (6a) where it is cooled Cool the sieve. The refrigerant whose temperature rises due to heat exchange with the object to be cooled is sucked into the compressor 2 through the pipe 6c and compressed again, repeats the above cycle, and performs a cooling cycle.

At this time, the temperature sensor 9 and the pressure sensor 10 detect the lubricating oil temperature t in the bottom of the compressor 2 and the suction pressure p of the refrigerant of the compressor 2 and this detection signal (output signal). Are sent to the oil temperature range calculating means 13 (step S1), the oil temperature range calculating means 13 obtains the compressor 2 obtained by the magnitude of the dilution degree of the lubricating oil by the refrigerant as shown in FIG. Since the lower limit temperature T _L of the inside is defined by the relational expression (T _L = f (p)) with the suction pressure p of the compressor 2, the suction and the output signal of the pressure sensor 10 are the relational expression. The lower limit temperature (T _L ) of the lubricant is calculated by the pressure (p), and the lower limit temperature (T _L ) is added to a predetermined temperature, for example, 20 degrees plus the temperature (T _L + 20 degrees) of the lubricant. It is calculated by the upper limit temperature (T _H) (step S2).

Subsequently, the temperature t of the lubricating oil, which is an output signal of the temperature sensor 9, is transmitted to the oil temperature determining means 14 by receiving the result of the calculation, and the allowable range between the lower limit temperature T _L and the upper limit temperature TH (oil temperature control). Range), and if it is within the allowable range, the solenoid valve driving means 15 is instructed to keep the solenoid valve 8a closed (step S4). The normal cooling operation of (1) is continued. If the temperature t of the lubricating oil which is the output signal of the temperature sensor 9 is not within the allowable range, the oil temperature determining means 14 causes the temperature t to exceed the upper limit temperature T _H. It is judged whether or not it is (step S5), and if exceeded, it is instructed to the solenoid valve driving means 15 to open the solenoid valve 8a (step S6). As a result, a part of the relatively low-temperature refrigerant passing through the condenser 3 flows into the compressor 2 through the bypass pipe 7 to suppress an excessive increase in the lubricating oil temperature in the compressor 2. If the temperature t does not exceed the upper limit temperature T _H , the solenoid valve 8a is closed (step S7) to stop the inflow of the refrigerant into the compressor 2 through the bypass pipe 7. Excessive reduction of the lubricating oil in the compressor 2 is suppressed.

On the other hand, the lower limit of the lubricant oil temperature (T _L ) of the compressor (2) is somewhat changed depending on the type of lubricant, but the relationship is that the value also increases when the suction pressure (p) increases in the first order almost to the suction pressure (p) Therefore, in the range where the temperature t of the lubricating oil is equal to or lower than the lower limit temperature T _L , the degree of dilution by the refrigerant of the lubricating oil increases, so that the lubrication of the sliding part of the compressor 2 becomes poor.

Thus, according to the cooling device 1 which concerns on this embodiment, the temperature t of the lubricating oil of the compressor 2, and the suction pressure p of a refrigerant | coolant are detected, and the oil temperature range calculation means 13 is based on the detection result. The oil temperature determining means 14 determines whether the temperature t of the lubricating oil is within a predetermined temperature allowable range of the lubricating oil, and according to the determination result, the oil temperature adjusting means 11 by the solenoid valve driving means 15. The opening and closing operation of the solenoid valve 8a of the bypass pipe 9 is controlled so that the flow rate of the relatively low-temperature refrigerant passing through the condenser 3 is properly adjusted so that the compressor from the bypass pipe 7 Since the lubricating oil in the compressor 2 is cooled in a timely manner as it flows into (2), the temperature of the lubricating oil in the compressor 2 is effectively maintained in a constant range without being excessively raised or lowered. As a result, the compressor 2 is suppressed from excessive temperature rise of the internal motor, and the lubricating performance of the lubricating oil for the sliding part is maintained well, thereby improving its efficiency.

In addition, the liquid backflow into the compressor 2 can be effectively prevented, so that the dilution degree of the refrigerant to the lubricating oil can be suppressed as small as possible, and through this, the lubrication performance of the sliding part of the compressor 2 can be maintained satisfactorily. Can be secured.

In addition, since the temperature sensor 9 is mounted on the surface of the container outside the compressor 2, it is not necessary to insert the temperature sensor 9 into the bottom of the compressor 2, and therefore, there is no need to perform special processing on the sealed container, thereby making it easy to manufacture. In addition, since the temperature sensor 9 has little trouble, maintenance and inspection are easy. In addition, since the flow rate adjusting means 8 provided in the bypass pipe 7 is a solenoid valve 8a and a capillary tube 8b, not only can it be configured at a low price, but also the internal structure of the control system can be simplified. have.

4 shows the cooling device 1A according to the second embodiment of the present invention. This cooling device 1A serves as a solenoid valve 8a and a capillary tube 8b of the bypass pipe 7 in the oil temperature control device 12 of the cooling device 1 according to the first embodiment. The flow rate adjusting means 8 and the solenoid valve driving means 15 which are made up are replaced by the flow rate adjusting means 8A and the electric expansion valve driving means (drive means) 15A which respectively consist of the electric expansion valve 16, and this electric transmission is carried out. An oil temperature control device 12A provided with an expansion valve driving means 15A to control the opening and closing operation of the electric expansion valve 16 is provided. Since the other structure is the same as the said cooling apparatus 1, the same code | symbol is attached | subjected to the same part as the said cooling apparatus 1, and the description about the structure is abbreviate | omitted. An oil temperature adjusting means 11A is formed by the electric expansion valve 16 and the bypass pipe 7.

In the case of the present cooling device 1A, when it is determined that the temperature t of the lubricating oil is within the allowable range in the oil temperature determining means 14 (step S3), as shown in FIG. The opening degree adjustment operation of the electric expansion valve 16 is controlled by 15A to hold the opening degree (step S4), and when it is determined that the temperature t of the lubricating oil is not within the allowable range, this temperature t is It is judged whether or not the upper limit temperature T _H is exceeded (step S5), and if it exceeds, the electric expansion valve 16 corresponds to a predetermined opening degree (for example, 10 times the minimum unit of the gradual opening degree). The opening degree is changed and adjusted step by step according to the temperature change of the lubricating oil (step S6), and the electric expansion valve 16 is changed and adjusted stepwise if not exceeding the upper limit temperature (T _H ) It is closed (step S7). Since other operations are the same as those of the cooling device 1, the same step will be given the same step and the description thereof will be omitted.

According to the cooling device 1A according to the present embodiment, not only the same effect as the cooling device 1 can be obtained, but also the electric power expansion valve 15 can adjust the change of the minute opening so that the bypass pipe ( It is possible to precisely control the flow rate of the refrigerant flowing into the compressor (2) through 7) to improve the lubricating oil temperature in the compressor (2) and the stability of the refrigeration cycle.

6 shows a cooling device 1B according to a third embodiment of the present application. The cooling device 1B includes the bypass pipe 7 and the solenoid valve 8a of the bypass pipe 7 in the oil temperature control device 12 of the cooling device 1 according to the first embodiment. The flow rate adjusting means 8 made of the capillary tube 8b is omitted, and a blower (oil temperature adjusting means) 17 is blown to the outer surface of the bottom of the compressor 2, and the oil temperature controlling means is provided. An oil temperature provided with a blower driving means (drive means) 15B that replaces the solenoid valve driving means 15 of (12) to control the operation of the blower 17 by the blower driving means 15B. The control apparatus 12B is provided. Since the other structure is the same as the said cooling apparatus 1, the same code | symbol is attached | subjected to the same part as the said cooling apparatus 1, and the description about the structure is abbreviate | omitted.

In the case of the present cooling device 1B, as shown in Fig. 7, when it is determined in the oil temperature determining means 14 that the temperature t of the lubricating oil is within the allowable range (step S3), the blower driving means 15B Operation of the blower 17 is controlled to maintain the operation (step S4), and if it is determined that the temperature t of the lubricating oil is not within the allowable range, the temperature t is the upper limit temperature ( It is judged whether or not T _H is exceeded (step S5), and if it exceeds, the blower 17 is operated at a predetermined rotational speed (step S6) and does not exceed the upper limit temperature T _H. If not, the operation of the blower 17 is stopped (step S7). Since other actions are the same as those of the cooling device 1, the same step is given the same step, and the description thereof is omitted.

According to the cooling device 1B according to the present embodiment, the upper and lower allowable ranges of the lubricating oil temperature t are determined according to the temperature t and the suction pressure p of the lubricating oil in the compressor 2, and accordingly the blower (oil temperature adjustment). The rotational motion of the means (17) is properly controlled and the lubricating oil in the compressor (2) is cooled in a timely manner by the blowing of the blower (17), so that it is effectively maintained at a constant range at all times. You can get it. Furthermore, by cooling the outer surface of the bottom of the compressor 2 directly by using the blower 17, the lubricating oil in the bottom of the compressor 2 can be effectively cooled by a simple configuration and similarly to the cooling apparatus 1, 1A. Since a part of the refrigerant flowing from the condenser 3 to the evaporator 5 does not flow to the bypass circuit 7, the stability of the refrigeration cycle can be improved.

Meanwhile, the blower 17 is configured to control rotation at a predetermined rotational speed and its stop operation by the operation of the blower driving means 15B according to the determination result by the oil temperature determining means 14, but is not limited thereto. Depending on the change in the lubricating oil temperature t, it is also possible to make the operation control combining a stepwise or continuous change of the rotational speed and the rotation stop.

On the other hand, in the case of the cooling devices 1, 1A, 1B according to the embodiment, the temperature sensor 9 is mounted on the surface of the container outside the compressor 2 to facilitate the above-described easy implementation. It is also possible to process the sealed container of the compressor 2 and insert the detection part of the temperature sensor 9 into the lubricating oil in the bottom of the compressor 2 so that the temperature of the lubricating oil can be detected directly.

According to the present invention, the following effects can be obtained.

According to the cooling device according to claim 1, the upper and lower allowable ranges of the lubricating oil temperature are determined by the oil temperature control device according to the lubricating oil temperature in the compressor and the suction pressure of the refrigerant, and thus the operation of the oil temperature adjusting means is appropriately controlled so that the lubricating oil in the compressor The timely cooling ensures that the temperature is effectively maintained in a constant range at all times without excessive rise or fall. As a result, excessive temperature rise of the motor inside the compressor can be suppressed to improve the compressor efficiency. In addition, it is possible to effectively prevent the backflow of the refrigerant liquid into the compressor, so that the dilution degree of the refrigerant with respect to the lubricating oil can be suppressed as small as possible, so that the lubrication performance of the sliding part of the compressor can be maintained satisfactorily and the operation reliability can be secured.

According to the cooling device according to claim 2, since the relatively low-temperature refrigerant discharged from the condenser flows into the compressor through a bypass circuit properly controlled, the inside of the compressor is effectively cooled by the refrigerant introduced into the bypass circuit, thereby lubricating oil. It can be reliably prevented that the temperature of is excessively raised or lowered.

According to the cooling device according to claim 3, not only can the flow rate adjusting means provided in the bypass circuit be inexpensively configured, but also the internal structure of the control system can be simplified.

According to the cooling device according to claim 4, it is possible to precisely control the flow rate of the refrigerant flowing into the compressor through the bypass circuit to improve the temperature of the lubricating oil in the compressor and the stability of the refrigeration cycle.

According to the cooling device according to claim 5, by cooling the outer surface of the compressor bottom directly through a blower, not only can the lubricant in the compressor bottom be efficiently cooled by a simple configuration, but also a part of the refrigerant flowing from the condenser to the evaporator flows into the bypass circuit. It is not necessary to improve the stability of the refrigeration cycle.

According to the cooling apparatus according to claim 6, since the temperature sensor is mounted on the surface of the container outside the compressor, it is easy to manufacture and the breakdown of the temperature sensor is small, so that maintenance and inspection can be easily performed.

1 is a system diagram showing a cooling apparatus according to a first embodiment of the present invention,

2 is a diagram showing the lower limit temperature of the lubricating oil temperature in the compressor to the suction pressure of the compressor through the refrigerant dilution degree,

3 is a flowchart for explaining the operation of the cooling apparatus according to the first embodiment of the present invention.

4 is a system diagram showing a cooling device according to a second embodiment of the present invention,

5 is a flowchart for explaining the operation of the cooling apparatus according to the second embodiment of the present invention.

6 is a system diagram showing a cooling device according to a third embodiment of the present invention,

7 is a flowchart illustrating the operation of the cooling apparatus according to the third embodiment of the present invention.

*** Explanation of symbols for main parts of drawing ***

1, 1A, 1B Chiller

2 compressor

3 condenser

4 Electric expansion valve (decompression device)

5 evaporator

6 Refrigerant circulation piping

7 Bypass Piping (Bypass Circuit)

8, 8A flow adjustment means

8a solenoid valve

8b capillary tube

9 Temperature sensor (oil temperature detection means)

10 Pressure sensor (suction pressure detection means)

11 Oil temperature adjusting means

12, 12A, 12B oil temperature controller

13 Oil temperature range calculation means

14 oil temperature determination means

15 Solenoid valve drive means (drive means)

15 A Electric expansion valve drive means (drive means)

15B blower drive means (drive means)

16 Electric Expansion Valve

17 Blower (oil temperature control means)

Claims (6)

In a cooling device provided with an oil temperature control device for connecting a compressor, a condenser, a pressure reducing device, and an evaporator through a refrigerant circulation pipe to configure a refrigeration cycle, and to control the temperature of the lubricating oil in the bottom of the compressor, The oil temperature control device includes oil temperature detection means for detecting a lubricating oil temperature in the compressor bottom, suction pressure detecting means for detecting a suction pressure of the compressor, and an output temperature of the lubricating oil in the compressor bottom in accordance with an output signal of the suction pressure detecting means. Oil temperature range calculating means for calculating the oil temperature control range, oil temperature determining means for comparing the oil temperature control range calculated by the oil temperature range calculating means and the output signal of the oil temperature detecting means, and actuating according to the output signal of the oil temperature determining means. Cooling apparatus comprising an oil temperature adjusting means for controlling the operation by the drive means to adjust the temperature of the lubricating oil in the compressor. The method of claim 1, The oil temperature adjusting means includes a bypass pipe for connecting a pipe connecting the condenser and the decompression device to a pipe connecting the evaporator and the compressor, and installed in the bypass circuit to control the opening and closing operation by the driving means. And a flow rate adjusting means for adjusting the flow rate of the refrigerant flowing in the bypass circuit. The method of claim 2, The flow rate adjusting means is made by connecting the solenoid valve and the capillary tube in series and the solenoid valve is characterized in that the opening and closing operation is controlled by the drive means. The method of claim 2, And the flow rate adjusting means includes an electric expansion valve, and the electric expansion valve controls the opening degree adjustment operation by the driving means. The method of claim 1, And the oil temperature adjusting means includes a blower whose rotational motion is controlled by the driving means and blows to the outer surface of the bottom of the compressor. The method according to any one of claims 1 to 5, And the oil temperature detecting means has a temperature sensor mounted on the surface of the vessel at the bottom of the compressor.