JP2720637B2 - Apparatus for preventing overheating of compressor motor in two-stage refrigerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for preventing overheating of a compressor motor in a two-stage refrigerator, more specifically, a low-stage compressor and a high-stage compressor, and a motor for driving each of these compressors coaxially. The compressor motor in a two-stage refrigerator having a compression device having a compressor for sucking gas refrigerant discharged from the low-stage compressor through the motor into the high-stage compressor. Overheating prevention device.

[0002]

2. Description of the Related Art Conventionally, a compressor motor in a single-stage refrigerator has been used.
As a device for preventing overheating of the heater,
As shown in FIG. 7, a compressor C having a compressor SC and a motor M for driving the compressor SC is known. A condenser CD, an expansion valve E, and a cooler CL are connected to the refrigerant discharge side of the compressor C via refrigerant pipes, respectively, and the motor is connected between the compressor SC and the motor M. A temperature detector (temperature-sensitive cylinder) S for detecting the degree of superheat of the refrigerant gas after passing through the temperature sensor M, and when the degree of superheat of the refrigerant gas detected by the temperature detector S exceeds a predetermined temperature. , The expansion valve E
The motor M is prevented from being overheated by controlling its opening so that the degree of superheat is constant and adjusting the gas flow to the compressor C side. .

[0003]

However, in the above-described compressor motor overheating prevention device, the evaporation temperature in the cooler CL is lower than a predetermined value and the condensation temperature in the condenser CD is lower than a predetermined value. At this time, since the motor protection thermo-CTP permanently installed in the motor M is activated to stop the operation of the refrigerator, there is a problem that the operation range of the refrigerator is limited.

In addition, the above-mentioned motor overheating prevention means is provided with a low
Also in the case of adopting a two-stage refrigerator having two high-stage compressors, as in the case of the single-stage type described above, in the region where the evaporation temperature is low (for example, -40 ° C or lower) and the condensation temperature is high, There is a problem that the protection thermostat is activated, the refrigerator is stopped, and the operation range of the refrigerator is limited. That is, FIG.
As shown in the above, when the evaporation temperature Te in the cooler is equal to or lower than a predetermined value and the condensation temperature Tc in the condenser is equal to or higher than a predetermined value,
In other words, in the area A indicated by hatching in the figure, as will be described later, the motor protection permanent thermostat operates to stop the operation of the refrigerator, so that the operation of the refrigerator is stopped. The range will be limited.

[0005] The amount of heat dissipation Q of the motor is represented by the following formula: K is the heat transfer coefficient, A is the heat transfer area, and ΔTm is the temperature difference between the coil surface temperature T of the motor and the passing gas temperature Tg.

[0006]

(Equation 1)

When the evaporating temperature Te in the cooler decreases, the amount W of refrigerant sucked into the compressor SC decreases and the heat transfer coefficient K decreases as shown in FIG. It becomes.

Accordingly, when the heat radiation amount Q of the motor is larger than the heat generation amount, that is, when the heat transfer coefficient K and the temperature difference ΔTm are large, the motor M can be sufficiently cooled, but the evaporation temperature Te is low. Then, since the amount W of the intake refrigerant decreases and the heat transfer coefficient K decreases, the heat release amount Q decreases even if the temperature difference ΔTm increases. As a result, the temperature detector S The coil temperature of the motor M becomes higher than the temperature of the refrigerant gas that has passed through the motor M, and the motor for protecting the motor operates, so that the area A shown in FIG. Low Te, condensation temperature Tc
Therefore, the operation in the region A where the air pressure is high becomes impossible, and the operation range is limited.

More specifically, in the case of operating a two-stage refrigerator, when the evaporation temperature Te decreases and the amount of refrigerant sucked into the compressor decreases, the cooling efficiency of the motor by gas decreases. Therefore, a large temperature gap is generated between the gas temperature passing through the motor and the actual coil temperature of the motor, and as a result, the gas temperature after passing through the motor is detected by the temperature detection. It is detected by a detector, and even if the overheating of the motor is prevented by adjusting the gas flow rate by controlling the opening degree of the expansion valve based on the detection result, based on the actual coil temperature of the motor,
Since the opening degree control of the expansion valve is performed, accurate overheat prevention of the motor cannot be performed, and the temperature of the motor rises to a temperature equal to or higher than a set temperature set by the protection thermostat, and is indicated by a hatched portion in FIG. In the area A, the protection thermo operates,
The operation of the refrigerator is stopped, and the operation range of the refrigerator is limited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to prevent the motor from being overheated accurately and surely without causing liquid compression on the compression device side. An object of the present invention is to provide a compressor motor overheat prevention device capable of expanding the operation range of a stage refrigerator.

[0011]

In order to achieve the above object, according to the present invention, as shown in FIGS. 1 to 4, a low-stage compressor 1a, a high-stage compressor 1b, and each of these compressors 1a, 1b having a motor 1c for coaxially driving the low-pressure compressor 1a.
-Stage compressor 1 in which gas refrigerant discharged from the compressor is sucked into the high-stage compressor 1b via the motor 1c.
And connected to the discharge side of the high-stage compressor 1b.
Pipe 31 branching from the outlet side of the condenser 2 and the branch pipe 31
An intermediate expansion valve 33, an intermediate cooler 32, and a return
An intermediate cooling device 3 comprising a return pipe 34;
34, the motor upstream of the refrigerant flow flowing through the motor 1c.
A refrigerator connected to the side is assumed .

According to the first aspect of the present invention, FIG.
As shown, the expansion valve 33 comprises a temperature-sensitive expansion valve,
The temperature sensing part 33a of the expansion valve is connected to the motor coil of the motor 1c.
The motor 1c
Downstream of the motor of the refrigerant flow flowing through the
The pressure equalizing pipe 33b of the expansion valve 33 for detecting the refrigerant pressure is connected.
Continued .

According to the second aspect of the present invention, as shown in FIG.
The expansion valve 33 comprises an electric valve, and the motor 1c
A coil temperature detector 7 for detecting the temperature of the motor coil, a pressure detector 8 for detecting the pressure on the downstream side of the motor in the refrigerant flow flowing through the motor 1c, and a refrigerant pressure for which the motor coil temperature is detected by the pressure detector 8. A superheat controller that adjusts the opening of the expansion valve 33 when the superheat is higher than the pressure equivalent saturation temperature by a predetermined degree of superheat, injects liquid refrigerant upstream of the flow of refrigerant flowing through the motor 1c, and suppresses the degree of superheat. 10 was provided .

According to the third aspect of the present invention, as shown in FIG.
The liquid refrigerant injection pipe 91 connected to the outlet side of the condenser 2
Is connected to the motor upstream side of the flow of the refrigerant flowing through the motor 1c, and the liquid refrigerant injection valve 91 is connected to the liquid refrigerant injection pipe 91.
While interposed, while providing an on-off valve 11 in the branch pipe 31, the coil temperature detector 7 for detecting a motor coil temperature of the motor 1c, a pressure detector for detecting the refrigerant pressure of the motor downstream of the refrigerant flow And the liquid refrigerant injection valve 9 when the motor coil temperature is higher than the saturation temperature corresponding to the refrigerant pressure detected by the pressure detector 8 by a predetermined degree of superheat.
2 injected liquid refrigerant open, and, and said coil temperature controller 12 to close the on-off valve 11 when the motor coil temperature is high is provided in this state.

[0015]

According to the first aspect of the present invention, as shown in FIG.
The intermediate expansion valve 33 constituting the intermediate cooling device 3 is
The expansion valve is used, and its temperature sensing part 33a controls the motor coil temperature.
The pressure equalizing pipe 33b is connected to the motor
1c connected to the motor downstream of the refrigerant flow
By using the expansion valve 33 constituting the intermediate cooling device 3
The liquid refrigerant can be injected, and the liquid refrigerant cools the motor 1c, thereby preventing the motor 1c from being overheated.

However, during the above-described refrigeration operation, even if the evaporation temperature is low and the refrigerant sucked into the compression device 1 side is small, and the heat transfer coefficient K is small, the liquid refrigerant is the refrigerant of the motor 1c. The motor 1 is injected into the front side of the flow.
c is prevented from overheating accurately and reliably. Therefore, the protection thermo for the motor 1c does not operate in the hatched area A shown in FIG. 5, and the operation range of the refrigerator is expanded. . Further, since the liquid refrigerant is injected into the motor 1C side, the liquid refrigerant does not flow into the high-stage compressor 1b, and the liquid compression in the high-stage compressor 1b is prevented.

[0017] will be able to inject the liquid refrigerant by using the expansion valve 33 constituting the intermediate cooling device 3, while it is possible to widen the street operating range described above, it can be simplified structure.

Further, the intermediate expansion valve 33 may be a motor operated valve.
In the invention described in Item 2, as shown in FIG. 3 , more precise superheat control can be performed while using the intermediate cooling device 3, and the configuration can be simplified while the operation range can be expanded. It is also possible to control the stop of the operation of the motor 1c at the upper limit of the motor coil temperature by using the superheat degree controller 10.

According to the third aspect of the present invention, as shown in FIG.
In addition to the motor cooling by controlling the degree of superheat on the downstream side of the motor by adjusting the opening of the injection valve 92, the on-off valve 11 is closed to stop the flow of the refrigerant to the intercooler 32, thereby reducing the amount of circulating refrigerant. Therefore, the control of the coil temperature by reducing the power of the motor 1c can be used together. Therefore, even if the motor cooling is insufficient with only the superheat control, the motor overheating can be more effectively prevented and the operation range can be more reliably expanded. You can do it.

[0020]

1 to 4 show a two-stage refrigerator using a reciprocating type compression apparatus 1 having a two-stage compression mechanism. Machine 1a,
1b and a two-stage compressor 1 having one motor 1c for driving the compressors 1a and 1b coaxially. A condenser 2 is provided on the refrigerant discharge side of the high- stage compressor 1b in the compressor 1.
The intermediate cooling device 3, the expansion valve 4, and the cooler 5 are connected via refrigerant pipes 6, respectively.
a from the motor 1c to the high-stage compressor 1
b, and further compressed, and the refrigerant compressed by the high-stage compressor 1b is circulated through the paths shown by solid arrows in each figure. The high-pressure liquid pipe 6a connected to the outlet side of the condenser 2 in the refrigerant pipe 6 includes:
A branch pipe 31 for branching the liquid refrigerant from the liquid pipe 6a is provided, the branch pipe 31 is connected to an intercooler 32, and an intermediate cooling expansion valve 33 is interposed in the branch pipe 31 to form the condenser 2
A part of the refrigerant having passed through is cooled by the intercooler 32 to supercool the refrigerant supplied to the cooler 5 as shown by a dotted arrow in each drawing. ,
A return pipe 34 that opens to the motor upstream side of the flow of the refrigerant flowing through the motor 1c is connected, and the refrigerant evaporating in the intercooler 32 passes between the low-stage compressor 1a and the motor 1c via the return pipe 34 The branch pipe 3
1. Intercooling expansion valve 33, intercooler 32 and return pipe 3
4, the intermediate cooling device 3 is formed.

In FIG. 1, reference numeral 4a denotes an opening of the expansion valve 4.
A temperature sensor that controls the temperature, a lead line is attached to the return pipe 34 side.
Reference numeral 33 denotes a temperature sensing part for controlling the opening degree of the intermediate expansion valve 33.
is there. 1 is excluded from the claims,
Although not a non-embodiment, the embodiment of FIGS.
The configuration will be described below in relation to the above. That is, the configuration is as follows.

That is, the motor 1c of the compressor 1 is provided with a coil temperature detector 7 for detecting the coil temperature of the motor 1c, and a motor downstream side is provided between the motor 1c and the high-stage compressor 1b. Pressure detector 8 for detecting refrigerant pressure
On the other hand, when the motor coil temperature detected by the temperature detector 7 is higher than the saturation temperature corresponding to the pressure of the refrigerant pressure detected by the pressure detector 8, when the low-stage compressor 1a and the motor 1c Refrigerant injection means 9 for injecting liquid refrigerant into
Was provided.

The liquid refrigerant injection means 9 shown in FIG. 1 is provided between the high pressure liquid pipe 6a connected to the outlet side of the condenser 2 and the motor upstream of the refrigerant flow flowing through the motor 1c. A liquid refrigerant injection pipe 91 is provided, and a liquid refrigerant injection valve 92 composed of an electric valve whose opening can be adjusted is interposed in the middle of the injection pipe 91, and the coil temperature detected by the coil temperature detector 7 is detected. The temperature T1 is compared with the pressure equivalent saturation temperature T2 of the refrigerant pressure detected by the pressure detector 8,
A superheat degree controller 93 for controlling the opening and closing of the injection valve 92 is provided. The coil detection temperature T1 detected by the temperature detector 7 is higher than the saturation temperature T2 of the refrigerant pressure detected by the pressure detector 8 by a predetermined degree. When the degree is high, that is, T1>
At the time of T2, the injection valve 92 is opened by the output signal from the superheat degree controller 93, and a part of the liquid refrigerant flowing from the injection pipe 91 through the high-pressure liquid pipe 10a flows through the motor 1c. The superheat degree of the refrigerant injected into the upstream of the motor and taken into the high-stage compressor 1b is defined as a predetermined superheat degree.
This is to prevent overheating of the motor 1c. A motor protection thermo is provided near the motor 1c, and the motor 1c is stopped by the operation of the thermo.

In the above construction, the temperature detector 7 detects the actual coil temperature of the motor 1c, and the pressure detector 8 detects the refrigerant pressure downstream of the motor of the refrigerant flowing through the motor 1c. When the coil temperature T1 detected by the temperature detector 7 is higher than the saturation temperature T2 of the refrigerant pressure detected by the pressure detector 8 by a predetermined degree of superheat, the output from the superheat controller 93 is output. The injection valve 92 is opened by the signal, and a part of the liquid refrigerant flowing from the injection pipe 91 through the high-pressure liquid pipe 6a is removed by the motor 1c.
Is injected into the motor upstream of the flow of the refrigerant flowing through the motor 1c, and the injection of the liquid refrigerant cools the motor 1c. Therefore,
Since overheating of the motor 1c is prevented, the operation of the motor for protecting the motor 1a can be prevented from being operated to stop the operation of the compressor, and the hatched area A shown in FIG.
And the operating range of the two-stage refrigerator can be expanded accordingly. As described above, when the coil temperature T1 detected by the temperature detector 7 is higher than the saturation temperature T2 corresponding to the refrigerant pressure detected by the pressure detector 8 by a predetermined degree of superheat, the temperature of the motor 1c is reduced. Since the liquid refrigerant is injected, the liquid refrigerant does not flow into the high-stage compressor 1b, and therefore, the liquid compression in the high-stage compressor 1b is prevented.

It should be noted that the coil temperature detector 7 can also be used as the motor protection thermo that is permanently installed in the motor 1c. In this case, the protection thermo is used to operate the two-stage refrigerator. A delay circuit for delaying the stop by a predetermined time is separately connected, and the operation of the protection thermostat and the pressure detector 8 causes the liquid refrigerant to be injected into the motor 1c side. Nevertheless, when the temperature of the motor 1c does not decrease even after the lapse of the predetermined time, the refrigeration operation is stopped by the protection thermo.

[0026] Further, those shown in FIG. 1, the liquid as a refrigerant injection means 9, the injection pipe 91 having the injection valve 92
However, without using the injection tube 91,
The branch pipe 31 and the return pipe 3 in the intermediate cooling device 3
4 and the intermediate expansion valve 33.

In this case, as shown in FIG. 2, the expansion valve 33 is a temperature-sensitive expansion valve, and its temperature-sensing portion 33a is used as a portion of the motor 1c where a motor coil temperature can be detected, such as a coil end or the like. The pressure equalizing pipe 33b of the expansion valve 33 is disposed in the slot groove of the stator and the motor 1
c, and is connected to the downstream side of the motor in the flow of the refrigerant flowing through c.

Therefore, also in this embodiment, when the motor coil temperature rises, the opening degree of the expansion valve 33 is controlled so that the superheat degree downstream of the motor becomes a predetermined superheat degree, and the branch pipe 3
1, the liquid refrigerant is injected from the return pipe 34 to the upstream side of the motor through the intercooler 32, and the motor 1c is cooled by the liquid refrigerant, and the condensing temperature Tc Is higher than a predetermined temperature and the evaporation temperature Te is low,
In other words, the operation of the refrigerator can be continued without being stopped even in the hatched area A shown in FIG. 5, and the operation range can be expanded.

As the liquid refrigerant injection means 9, FIG.
The branch pipe 31, the return pipe 34 and the intermediate expansion valve 3
When utilizing 3, the expansion valve 33 may be an electric valve.

In this case, as shown in FIG. 3, a coil temperature detector 7 for detecting the motor coil temperature of the motor 1c.
And a pressure detector 8 for detecting the refrigerant pressure on the downstream side of the motor in the flow of the refrigerant flowing through the motor 1c, and the motor coil temperature is determined from the saturation temperature corresponding to the pressure of the refrigerant pressure detected by the pressure detector 8. When the degree of superheat is high, the degree of opening of the expansion valve 33 is adjusted, and a superheat degree controller 10 for controlling the degree of superheat by injecting a liquid refrigerant into the motor upstream of the refrigerant flow flowing through the motor 1c. Is provided.

Therefore, also in this embodiment, when the motor coil temperature rises, the degree of opening of the expansion valve 33 is adjusted by the superheat degree controller 1 so that the degree of superheat downstream of the motor becomes a predetermined degree.
Under the output of 0, liquid refrigerant is injected from the branch pipe 31 through the intercooler 32 to the upstream side of the motor from the return pipe 34, and the liquid refrigerant is injected by the liquid refrigerant. The heater 1c is cooled. In this case, since the coil temperature detector 7 is connected to the input portion of the superheat degree controller 10 as in the embodiment of FIG.
When the motor coil temperature reaches the upper limit temperature, the motor 1c
A control system for shutting down can be incorporated.

Further, when forming a liquid refrigerant injection pipe 91 having a liquid refrigerant injection valve 92 as in the embodiment shown in FIG.
An on-off valve 11 is provided in a branch pipe 31 of the intermediate cooling device 3,
The liquid refrigerant injection valve 92 is opened when the motor coil temperature is higher than the saturation temperature corresponding to the refrigerant pressure detected by the pressure detector 8 by a predetermined degree of superheat, and when the motor coil temperature is higher, the on-off valve 11 is opened. May be closed.

That is, in this case, as shown in FIG. 4, a liquid refrigerant injection pipe 91 is connected to the high-pressure liquid pipe 6a, and this injection pipe 91 is connected to the motor upstream side, that is, in FIG.
And a liquid refrigerant injection valve 92 is connected to the injection pipe 91.
In addition, the on-off valve 11 is provided on the branch pipe 31, and the coil temperature detector 7 and the pressure detector 8 are provided similarly to the embodiment shown in FIGS. 1 and 3, and the motor coil is provided. When the temperature is higher than the saturation temperature corresponding to the refrigerant pressure detected by the pressure detector 8 by a predetermined degree of superheat, the liquid refrigerant injection valve 92 is opened to inject the liquid refrigerant, and the motor coil temperature is further higher. At this time, a coil temperature controller 12 for closing the on-off valve 11 is provided.

Therefore, in this embodiment, when the motor coil temperature rises, the liquid refrigerant injection valve is controlled so that the superheat degree downstream of the motor becomes a predetermined superheat degree based on the output from the coil temperature controller 12. The opening of 92 is controlled, and the liquid refrigerant is injected from the liquid refrigerant injection pipe 91 to the upstream side of the motor, and the motor 1c is cooled by the liquid refrigerant, and the degree of superheat is controlled. If the motor coil temperature rises in this state, that is, if the supercooling control alone does not provide sufficient motor cooling, the flow of the refrigerant flowing through the intercooler 32 can be stopped by closing the on-off valve 11. Since the amount of circulating refrigerant can be reduced accordingly, the intercooler 3
Although the function of 2 is sacrificed, the power of the motor 1c is reduced, and the amount of heat generated by the motor 1c can be suppressed and cooling can be performed effectively.

The above-described embodiments all use the reciprocating compressor 1, but have a low-stage compressor 1a and a high-stage compressor 1b.
The present invention can also be applied to a two-stage refrigerator using a screw compression device in which 1b is driven coaxially by one motor 1c.

[0036]

[0037]

[0038]

[0039]

[0040]

[Brief description of the drawings]

FIG. 1 is a piping diagram of a two-stage refrigerator showing a premise of the present invention.

FIG. 2 is a piping diagram of a two-stage refrigerator showing a first embodiment of the present invention.

FIG. 3 is a piping diagram of a two-stage refrigerator showing a second embodiment of the present invention.

FIG. 4 is a piping diagram of a two-stage refrigerator showing a third embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an operation region of a refrigerator to which the present invention is applied.

FIG. 6 is a graph showing a relationship between a suctioned refrigerant amount and an evaporation temperature.

FIG. 7 is a refrigerant piping system diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 2 stage compressor 1a Low stage compressor 1b High stage compressor 1c Motor 2 Condenser 3 Intercooler 7 Coil temperature detector 8 Pressure detector 9 Liquid refrigerant injection means 10 Superheat degree controller 11 Open / close valve 12 Coil Temperature controller 31 Branch pipe 32 Intercooler 33 Intermediate expansion valve 34 Return pipe 91 Liquid refrigerant injection pipe 92 Liquid refrigerant injection valve

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References Jikken 39-1081 (JP, Y1) Jigoku 56-15485 (JP, Y2)

Claims (3)

(57) [Claims] 1. A low-stage compressor 1a, a high-stage compressor 1b, and a motor 1c for driving the compressors 1a and 1b coaxially, and a gas refrigerant discharged from the low-stage compressor 1a is supplied to the motor. A branch pipe 31 that branches off from the outlet side of the condenser 2 that is connected to the discharge side of the high-stage compressor 1b; Intermediate expansion valve 3 interposed in branch pipe 31
3. An apparatus for preventing overheating of a compressor motor in a refrigerator in which an intermediate cooling device 3 including an intermediate cooler 32, an intermediate cooler 32, and a return pipe 34 is provided, and the return pipe 34 is connected to a motor upstream side of a refrigerant flow flowing through the motor 1c. And the expansion valve 33
Comprises a temperature-sensitive expansion valve, and a temperature-sensitive portion 33a of the expansion valve is disposed at a position where the temperature of the motor coil of the motor 1c can be detected. An overheating prevention device for a compressor motor in a two-stage refrigerator, wherein an equalizing pipe 33b of the expansion valve 33 for detecting a refrigerant pressure on a side of the compressor is connected. 2. A low-stage compressor 1a, a high-stage compressor 1b, and a motor 1c for driving the compressors 1a and 1b coaxially. The gas refrigerant discharged from the low-stage compressor 1a is supplied to the motor. A branch pipe 31 that branches off from the outlet side of the condenser 2 that is connected to the discharge side of the high-stage compressor 1b; Intermediate expansion valve 3 interposed in branch pipe 31
3. An apparatus for preventing overheating of a compressor motor in a refrigerator in which an intermediate cooling device 3 including an intermediate cooler 32, an intermediate cooler 32, and a return pipe 34 is provided, and the return pipe 34 is connected to a motor upstream side of a refrigerant flow flowing through the motor 1c. And the expansion valve 33
Comprises a motor-operated valve, a coil temperature detector 7 for detecting a motor coil temperature of the motor 1c, a pressure detector 8 for detecting a refrigerant pressure on a downstream side of the motor in a refrigerant flow flowing through the motor 1c, and a motor coil temperature of When the degree of superheat is higher than the saturation temperature of the refrigerant pressure detected by the pressure detector 8 by a predetermined degree of superheat, the opening degree of the expansion valve 33 is adjusted, and the liquid refrigerant is injected upstream of the flow of the refrigerant flowing through the motor 1c. And a superheat controller 10 for controlling the degree of superheat by controlling the superheat of the compressor motor in the two-stage refrigerator. 3. A low-stage compressor 1a, a high-stage compressor 1b, and a motor 1c for driving the compressors 1a and 1b coaxially. The gas refrigerant discharged from the low-stage compressor 1a is supplied to the motor. A branch pipe 31 that branches off from the outlet side of the condenser 2 that is connected to the discharge side of the high-stage compressor 1b; Intermediate expansion valve 3 interposed in branch pipe 31
3. An apparatus for preventing overheating of a compressor motor in a refrigerator in which an intermediate cooling device 3 including an intermediate cooler 32, an intermediate cooler 32, and a return pipe 34 is provided, and the return pipe 34 is connected to a motor upstream side of a refrigerant flow flowing through the motor 1c. A liquid refrigerant injection pipe 91 connected to the outlet side of the condenser 2 is connected to a motor upstream side of a refrigerant flow flowing through the motor 1c, and the liquid refrigerant injection pipe 91 is connected to the liquid refrigerant injection pipe 91 through a liquid refrigerant injection valve 92. While the on-off valve 11 is provided in the branch pipe 31, the motor 1
C coil temperature detector 7 for detecting the motor coil temperature of c
A pressure detector 8 for detecting a refrigerant pressure on the downstream side of the motor in the refrigerant flow;
The liquid refrigerant injection valve 92 is opened to inject the liquid refrigerant when the superheat is higher than the pressure equivalent saturation temperature of the refrigerant pressure detected by the above, and the on-off valve 11 is turned on when the motor coil temperature is high in this state. An overheating prevention device for a compressor motor in a two-stage refrigerator, comprising a closing coil temperature controller 12.