JP2002081391A - Screw compressor for refrigeration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw compressor for a refrigeration device capable of controlling a revolution number of a motor adapted for a cooling thermal load only by an inverter control without causing an excess load of the motor. SOLUTION: In the screw compressor 1A for a refrigeration device 10A using a motor 22 inverter-controlled as a driving part, a suction pressure detector D3 as a thermal load detection means for detecting a cooling thermal load; a motor coil temperature detector D1 as a means for detecting a load state of the motor 22; and a controller 26 for reducing a revolution number of the motor 22 in the case where it is judged that an ability of the compressor is excess based on a pressure signal from the detector D3, maintaining the revolution number in the case where it is judged that the ability is not excess and is not lacked, reducing the revolution number in the case where it is judged that the load state is excess based on a temperature signal from the detector D1 and increasing the revolution number in the other cases in the case where the ability is lacked are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw compressor for a refrigerating machine driven by a motor controlled by an inverter.

[0002]

2. Description of the Related Art Conventionally, there has been known a screw compressor for a refrigerating apparatus in which the rotation speed of a motor for driving a compressor main body and a liquid injection pump is controlled in accordance with an increase and a decrease in a load (Japanese Patent Laid-Open No. Sho 57-57). No. 18484). This screw compressor has a suction pressure detector which detects a suction pressure having a one-to-one relationship with a cooling heat load at a suction portion thereof, and outputs a pressure signal output from the suction pressure detector to a pressure controller. , And the rotation speeds of a motor for driving the compressor body and a motor for driving the liquid injection pump are simultaneously controlled. Further, a screw compressor for a refrigeration system which improves the efficiency of a low partial load region by adding a capacity control method using an inverter to a stepless capacity control mechanism using a slide valve is disclosed in Japanese Patent Application Laid-Open No. 59-211790. ing.

[0003]

Problems to be Solved by the Invention
In the case of the screw compressor disclosed in Japanese Patent Publication No. 84, when the pressure detected by the suction pressure detector is higher than a set pressure value, control for increasing the rotation speed of the motor is performed. For this reason, there is a problem that the motor tends to be overloaded and the durability of the motor is reduced.

Further, in the case of the screw compressor disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 59-211790, the compressor has a complicated structure because a slide valve is provided. Further, in the case of this screw compressor, a capacity of 10
When it is in the range of 0 to 75%, the inverter is not used, that is, the commercial power supply is directly used without passing through the inverter, and there is a problem that the inverter is not sufficiently used. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described conventional problems, and it is possible to control the rotation speed of a motor suitable for a cooling heat load without constantly overloading the motor via an inverter. It is an object of the present invention to provide a screw compressor for a refrigeration system.

[0005]

In order to solve the above-mentioned problems, a first aspect of the present invention is to detect a cooling heat load in a screw compressor for a refrigeration system driven by a motor whose rotation speed is controlled via an inverter. Heat load detecting means, at least one load state detecting means for detecting any one of the factors indicating the load state of the motor, and a compression function based on a heat load signal inputted from the heat load detecting means, If it is determined that there is, the rotation speed of the motor is reduced, and if it is determined that the compression function is neither excessive nor insufficient, the rotation speed of the motor is maintained and the compression function is maintained. If it is determined that is insufficient, based on the load state signal input from the load state detection means, if it is determined that the load state is excessive, the rotational speed of the motor is reduced, Other And configured to include an adjustment gauge for increasing the rotational speed of the motor in the case.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, the controller determines whether the load state is excessive when the load state is the rotation speed of the motor.
The determination is made based on whether or not the motor rotation speed indicated by the input load state signal exceeds the upper limit rotation speed of the motor determined in accordance with the suction pressure. When the number of rotations is decreased, and when the number of rotations is not exceeded, the rotation speed of the motor is increased in the other cases.

[0007]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a refrigeration apparatus 10A to which a screw compressor 1A according to the present invention is applied. This refrigeration apparatus 10A is a circulating flow in which a refrigerant flows through a screw compressor 1A, a condenser 11, an expansion valve 12, and an evaporator 13. Road 14
Is formed. The screw compressor 1A includes a pair of male and female screw rotors 21 meshing with each other, a motor 22 for rotating the screw rotor 21, a discharge unit 23, and a motor coil temperature detector D1.
4 is operated by the electric power supplied via the inverter 25. The condenser 11 has a cooling water inlet C
i and a cooling water outlet Co are provided, and the evaporator 13 is provided with a cooled liquid inlet Bi and a cooled liquid outlet Bo. In addition, a superheat degree detector D2 for detecting the degree of superheat of the refrigerant gas discharged from the evaporator 13 is provided on the secondary side of the evaporator 13 with respect to the circulation flow path 14, and according to the degree of superheat detected by this, The opening of the expansion valve 12 is controlled. Further, a suction pressure detector D3 for detecting the suction pressure of the screw compressor 1A is provided on the secondary side of the evaporator 13, and a pressure signal indicating the detected pressure is sent from the suction pressure detector D3 to the controller 26. And a temperature signal indicating the detected temperature is also input from the motor coil temperature detector D1 to the controller 26. Here, the suction pressure is a factor indicating the cooling heat load of the refrigeration apparatus 10A, and the motor coil temperature is a factor indicating the load state of the motor 22. Then, the frequency of the power is converted by the inverter 25 based on the two signals, and the motor 22 is controlled as described later.

As shown in FIG. 2, the suction pressure of the screw compressor 1A and the cooling heat load of the refrigeration system 10A have a one-to-one relationship, and the cooling heat load increases as the suction pressure increases. If the suction pressure is too low, the cooling heat load is small, and the performance of the screw compressor 1A is excessive, and the rotation speed of the motor 22 is reduced to lower the performance of the screw compressor 1A, thereby reducing power consumption. Should be reduced. Conversely, if the suction pressure is too high, the cooling heat load is large, the capacity of the screw compressor 1A is insufficient, and the rotational speed of the motor 22 is increased to increase the screw compressor 1A.
It is necessary to improve A's ability. Therefore, neither the X area where the suction pressure is too low, the Z area where the suction pressure is too high, nor the height, and the Y area where the rotation speed of the motor 22 does not need to be changed,
The boundary value of each area can be set in advance and the controller 2
6 is set in advance.

Next, control of the motor 22 during the operation of the refrigeration system 10A will be described with reference to FIG. First, the screw compressor 1A is started,
When the refrigerating apparatus 10A is in the operating state, the controller determines in a first step whether the suction pressure belongs to any of the X, Y, and Z regions described above. Proceed to the step of reducing the number of revolutions,
If it belongs to the Y region, it means that there is no need to change the rotation speed of the motor 22, that is, the rotation speed is maintained, and the process returns to the first step. On the other hand, when the suction pressure belongs to the Z region, it is necessary to increase the rotation speed of the motor 22 to increase the performance of the screw compressor 1A. However, if the rotation speed of the motor 1A This overload condition must be avoided because 22 is overloaded.

Therefore, when the suction pressure belongs to the Z region, the motor coil temperature is equal to or less than a predetermined upper limit (Y
ES) or not (NO), and the controller 26 makes this determination. In the case of YES, the process proceeds to a step of increasing the rotation speed of the motor 22, and a signal for increasing the power frequency is output from the controller 26 to the inverter 25, so that the rotation speed of the motor 22 is increased. On the other hand, in the case of NO, since the motor 22 is considered to be in an overload state, the process proceeds to the step of reducing the number of revolutions of the motor 22, and even if the suction pressure is in the Z region, the controller 26 On the other hand, a signal for reducing the frequency of the electric power is output, and the rotation speed of the motor 22 is reduced. After passing through these steps of changing the number of revolutions of the motor 22, the process returns to the first step in any case, and the above steps are repeated. As described above, the capacity of the screw compressor 1A is adjusted according to the change in the cooling heat load without causing the motor 22 to be overloaded.

FIG. 4 shows a refrigerating apparatus 10B using another screw compressor 1B according to the present invention. Portions common to those of the refrigerating apparatus 10A shown in FIG. I do. This refrigeration apparatus 10B is provided with a cooled liquid temperature detector D4 in the flow path of the cooled liquid exiting the evaporator 13 instead of the suction pressure detector D3 shown in FIG. A temperature signal indicating the detected temperature is input to the controller 26 from the controller D4. As described above, the suction pressure has a one-to-one correspondence with the cooling heat load, and the cooling heat load is indicated by the cooled liquid outlet Bo of the evaporator 13 or the temperature of the cooled liquid at the downstream side thereof. It is. Therefore, the refrigeration system 10B shown in FIG. 4 is substantially the same as the refrigeration system 10A shown in FIG. 1, and based on the temperature signal from the cooled liquid temperature detector D4, when the suction pressure is X, Y, Z. It is also possible to determine to which region it belongs, and the flowchart shown in FIG. 3 applies to the refrigerating apparatus 10B shown in FIG.

FIG. 5 shows a refrigerating apparatus 10C to which still another screw compressor 1C according to the present invention is applied, and portions common to the refrigerating apparatus 10A shown in FIG. Omitted. This refrigeration system 10C
Replaces the motor coil temperature detector D1 shown in FIG.
A current detector D5 for detecting the magnitude of the motor current of the electric power supplied to the motor 22 is provided.
, A current signal indicating the detected current is input to the controller 26. And in this refrigerating device 10C,
As shown in FIG. 6, instead of the step of determining whether the motor coil temperature is equal to or lower than the upper limit in FIG. 3, control is performed in which a step of determining whether the motor current is equal to or lower than a predetermined upper limit is provided. That is, the motor current is equal to or less than the upper limit (YE
In the case of S), it is considered that the motor 22 is not in the overload state, so the process proceeds to the step of increasing the motor rotation speed, and if the motor current is not below the upper limit (NO), the motor 22 is overloaded. Since the state is considered to be in the state, the process proceeds to the step of reducing the motor speed. In this control, the overload state of the motor 22 is determined based on the motor current. Except for this point, the other control is substantially the same as the control shown in FIG.

FIG. 7 shows a refrigerating apparatus 10D to which still another screw compressor 1D according to the present invention is applied. Parts common to the refrigerating apparatus 10D shown in FIG. Omitted. This refrigeration system 10D
Replaces the motor coil temperature detector D1 shown in FIG.
A discharge temperature detector D6 for detecting the temperature of the refrigerant gas compressed and discharged from the screw rotor 21 is provided in the discharge section 23. A temperature signal indicating the detected temperature is input to the controller 26 from the discharge temperature detector D6. It is supposed to be. In this refrigeration apparatus, as shown in FIG. 8, instead of the step of determining whether the motor coil temperature in FIG. 3 is equal to or lower than the upper limit, the discharge temperature of the compressed refrigerant gas from the screw rotor 21 is set to a predetermined upper limit. Control is provided with a step of determining whether the value is equal to or less than the value. That is, when the discharge temperature is equal to or lower than the upper limit value (YES), it is considered that the motor 22 is not in the overload state. In this case, the motor 22 is considered to be in an overloaded state, and the process proceeds to the step of reducing the motor speed. In this control, the overload state of the motor 22 is determined based on the discharge temperature. Except for this point, the other control is substantially the same as the control shown in FIG.

FIG. 9 shows a refrigerating apparatus 10E to which still another screw compressor 1E according to the present invention is applied. Parts common to the refrigerating apparatus 10A shown in FIG. Omitted. This refrigeration system 10E
Replaces the motor coil temperature detector D1 shown in FIG.
Motor rotation speed detector D7 for detecting the rotation speed of motor 22
The rotation speed signal indicating the detected rotation speed is input to the controller 26 from the motor rotation speed detector D7. Then, in this refrigeration apparatus 10E, as shown in FIG. 10, instead of the step of determining whether or not the motor coil temperature in FIG. 3 is equal to or lower than the upper limit, it is determined whether the motor rotation speed is equal to or lower than a predetermined upper limit. Control with steps is performed. That is, the motor speed is equal to or less than the upper limit value (YES).
In the case of, the motor 22 is not considered to be in an overloaded state, so the process proceeds to the step of increasing the motor speed. If the motor speed is not equal to or less than the upper limit (NO), the motor 22 is in an overloaded state. Therefore, the process proceeds to the step of reducing the motor rotation speed. This control is performed by the motor 2
The overload state of No. 2 is determined on the basis of the motor rotation speed. Except for this point, the other control is substantially the same as the control shown in FIG.

The motor speed is controlled by the inverter 25.
Can also be determined from the frequency of the current output from the inverter 25. A frequency detector D7 for detecting this frequency is provided in the inverter 25 or on its secondary side instead of the motor rotation speed detector D7. A frequency signal indicating the magnitude of the detection frequency may be input to the controller 26 from the controller D7. In this case, a step of determining whether the frequency is equal to or less than a predetermined upper limit value is provided instead of the step of determining the magnitude of the motor rotation speed in FIG. In the case of each of the above-described refrigerating devices, only one type of the motor coil temperature detector D1, the liquid to be cooled temperature detector D4, the current detector D5, and the like is provided and the motor 22 is provided.
Although the present invention was designed to judge the load state, the present invention is not limited to one type of detector, a plurality of detectors are appropriately selected from these detectors, and the plurality of detectors are provided. It also includes refrigeration equipment. The detector to be selected may be all or some of the above-described detectors for determining the load state of the motor 22, and the combination thereof is arbitrary. Next, one using two types of detectors among the above-described detectors for determining the load state of the motor 22,
A description will be given by taking, as an example, one using three types of detectors and one using four types of detectors. It goes without saying that the invention is not limited to this exemplary detector combination.

FIG. 11 shows a refrigerating apparatus 10F to which a screw compressor 1F provided with a motor coil temperature detector D1 and a discharge temperature detector D6 is applied. And the description is omitted. As shown in FIG.
Then, it is determined to which region X, Y, or Z the suction pressure belongs. If it is determined that the suction pressure belongs to the Z region, before the step of increasing the motor rotation speed is reached, the two detectors Two decision steps regarding the signal are inserted.
That is, if it is determined that the motor coil temperature belongs to the Z region, the process proceeds to a step of determining whether or not the motor coil temperature is equal to or lower than the upper limit value (YES). If NO, the motor 22 is in an overloaded state. Therefore, the process proceeds to the step of reducing the motor rotation speed. In the case of YES, it cannot be said that the motor 22 is in an overload state as long as it is determined only from the motor coil temperature, so the process proceeds to a step of determining whether or not the discharge temperature is equal to or lower than the upper limit (YES). In the case of NO, the motor 22 is considered to be in an overload state,
The process proceeds to a step of decreasing the motor speed, and if YES, it is determined that the motor 22 is not in an overloaded state, and the process proceeds to a step of increasing the motor speed. Hereinafter, it is the same as each control flow mentioned above. in this way,
In the refrigerating apparatus 10F, whether the motor 22 is in an overload state is determined twice based on two factors. The motor coil temperature detector D1 and the discharge temperature detector D6
The order of the two judgment steps regarding is not limited and is arbitrary.

FIG. 13 shows a motor coil temperature detector D1,
The figure shows a refrigerating apparatus 10G to which a screw compressor 1G provided with a current detector D5 in addition to the discharge temperature detector D6 is used. Omitted. As shown in FIG. 14, in the refrigerating apparatus 10G, the motor current is further reduced to the upper limit or less (YES) in the flowchart shown in FIG.
This is a control flow in which a step of determining whether or not (NO) is added. In the refrigeration apparatus 10G, the motor 2
Whether or not 2 is overloaded is determined in triplicate based on three factors. The motor coil temperature detector D1,
The order of the three determination steps for the discharge temperature detector D6 and the current detector D5 is not limited and is arbitrary.

FIG. 15 shows a motor coil temperature detector D1,
This shows a refrigerating device 10H to which a screw compressor 1H provided with a motor rotation speed detector D7 in addition to a discharge temperature detector D6 and a current detector D5 is used. Numbers are assigned and explanations are omitted. As shown in FIG. 16, in the refrigeration apparatus 10H, a control flow is added to the flowchart shown in FIG. 14, which further includes a step of determining whether the motor rotation speed is equal to or less than an upper limit value (YES) or not (NO). In the refrigerating apparatus 10H, whether or not the motor 22 is in an overload state is determined fourfold based on four factors. The order of the four determination steps for the motor coil temperature detector D1, the discharge temperature detector D6, the current detector D5, and the motor speed detector D7 is not limited and is arbitrary. Further, in each of the refrigerating devices shown in FIG. 5 and the following, a coolant temperature detector D4 may be provided instead of the suction pressure detector D3. In this case, the cooling fluid temperature detector D4 The suction temperature is derived based on the temperature signal, and it is determined in the control flow whether the suction pressure belongs to any of the above-described X, Y, and Z regions.

By the way, the motor of the screw compressor for the refrigeration system is selected on the basis of the summer time when the discharge pressure of the compressor becomes maximum. For example, in summer, the water inlet temperature of the water-cooled condenser 11 is about 32 ° C., the condensing temperature CT of the refrigerant is 40 ° C., and the discharge pressure of the compressor is 15.6 ata corresponding to the condensing temperature CT of 40 ° C. Become. Therefore, as the motor, a motor capable of withstanding the discharge pressure of 15.6 atm is selected within the range of the normally assumed evaporation temperature ET. The nominal output of this motor is
5kw. When this refrigeration system is used in winter, if the water inlet temperature drops, for example, to 20 ° C.,
The condensation temperature CT is 28 ° C. and the discharge pressure is 11.5 ata.
And the required power of the motor at this time is smaller than 55 kw. That is, if the number of rotations of the motor is the same, the power consumption (kw) and the motor current (A) of the motor are, as indicated by the solid line in FIG. As indicated by the dashed line in 17, the temperature is lower in winter when the condensation temperature CT = 28 ° C.

For this reason, for example, in each screw compressor, if the power consumption of the motor is prevented from exceeding 55 kw and the rotation speed of the motor is prevented from exceeding 6000 rpm, a solid line in FIG. 18 is exemplified. When the condensing temperature CT in summer is 40 and the condensing temperature CT in winter is 28 ° C. as exemplified by a dashed line, the upper limit value of the motor speed is determined corresponding to the suction pressure. further,
For example, in the summertime shown by the solid line, the evaporation temperature ET = −30 ° C.
And the power consumption of the motor is 55kw and the rotation speed of the motor is 355
Even in the case of 0 rpm, in the wintertime indicated by the dashed line, if the power consumption of the motor is increased to 55 kw at the evaporation temperature ET = −30 ° C., the rotation speed of the motor increases to about 5000 rpm. Therefore, in the screw compressors 1E and 1H described above, as a criterion for determining whether or not the motor rotation speed is equal to or less than the predetermined upper limit, for example, as described above, the motor rotation speed determined in advance according to the suction pressure is Preferably, the upper limit is used as a reference.

Further, when the above-mentioned screw compressors 1E and 1H are oil-cooled, an oil recovery device 32 having an oil separation element 31 is provided in the discharge section 23 as shown in FIG. ing. And screw rotor 2
The refrigerant gas sucked by 1 is compressed while being injected into an oil passage (not shown), and is discharged to the oil recovery unit 32 together with the oil and the oil injected into the bearings. Oil recovery unit 3
In 2, the compressed refrigerant gas and oil are separated and recovered,
After passing through the oil separation element 31, the clean refrigerant gas from which the oil has been removed is sent to the condenser 11. Meanwhile, oil recovery unit 3
The oil recovered in Step 2 is guided to the oil flow path in which an oil cooler is interposed and circulated.

When the above-described screw compressors 1E and 1H are of the oil-cooled type, the upper limit value of the motor speed is taken into consideration, as shown in FIG. 20, by the gas flow rate in the oil recovery unit 32. There is a need. In other words, the solid line in FIG. 20 corresponds to the solid line in FIG. 18, and indicates the gas flow velocity at the motor speed shown by the solid line in FIG.
At 0, the one-dot chain line indicates the gas flow rate at the motor rotation speed indicated by the one-dot chain line in FIG. 18, and in this winter season, the allowable flow velocity upper limit indicated by the broken line in FIG. 20 may be exceeded. When the gas flow rate exceeds the upper limit of the flow rate, the separation of the oil and the refrigerant gas in the oil separation element 31 becomes incomplete, and a part of the oil
And the refrigeration system cannot be operated. A hatched portion in FIG. 20 indicates a region where the operation of the refrigeration apparatus cannot be performed. Therefore, in the case of wintertime indicated by the one-dot chain line in FIG. 20, in the portion where the suction pressure corresponds to the hatched portion, the motor speed is further reduced as shown by the two-dot chain line in FIG. There is a need. Therefore, when the above-described screw compressors 1E and 1H are oil-cooled,
Regarding the upper limit value of the motor rotation speed, in consideration of the gas flow rate, the motor is determined according to the suction pressure within a range not exceeding the flow rate upper limit, that is, within a range not exceeding the value indicated by the two-dot chain line. It is preferable to employ an upper limit rotational speed.

It should be noted that the above numerical values are merely examples, and the present invention is not limited to these numerical values. Although FIG. 18 shows straight lines, these lines indicating the upper limit of the number of rotations of the motor are not necessarily straight lines but may be curved lines.

[0024]

As is apparent from the above description, according to the first invention, in a screw compressor for a refrigeration system in which a motor whose rotation speed is controlled via an inverter is a driving unit,
Heat load detecting means for detecting a cooling heat load, at least one load state detecting means for detecting any factor indicating the load state of the motor, and compression based on a heat load signal input from the heat load detecting means. When it is determined that the functional force is excessive, the rotational speed of the motor is reduced, and when it is determined that the compressive functional force is neither excessive nor insufficient, the rotational speed of the motor is maintained. However, when it is determined that the compression function is insufficient, based on the load state signal input from the load state detection means, when it is determined that the load state is excessive, the rotation of the motor is determined. And a controller for reducing the number, and otherwise increasing the rotation speed of the motor.

For this reason, the slide valve is not used, the inverter is always used, and the motor is not overloaded.
The number of rotations of the motor can be controlled appropriately in response to the cooling heat load, and the durability of the motor can be improved and the power consumption can be reduced.

According to the second invention, in addition to the configuration of the first invention, the controller determines whether the load condition is excessive when the load condition is the rotation speed of the motor. Is performed based on whether or not the motor rotation speed indicated by the input load state signal exceeds an upper limit rotation speed of the motor determined according to the suction pressure. When the number is not exceeded, and when the number is not exceeded, the number of rotations of the motor is increased in the other cases. For this reason, in addition to the effect of the first invention, compared to the condensation temperature adopted as one of the design conditions,
Even under the condition where the actual condensing temperature is lowered, it is possible to avoid the occurrence of a situation in which the refrigerating apparatus cannot be operated due to, for example, the outflow of oil from the oil-cooled compressor to the condenser.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a refrigerating apparatus to which a screw compressor according to the present invention is applied.

FIG. 2 is a diagram showing a relationship between a suction pressure of a screw compressor and a cooling heat load in the refrigeration apparatus shown in FIG.

FIG. 3 is a flowchart showing control on a screw compressor in the refrigeration apparatus shown in FIG.

FIG. 4 is a view schematically showing a refrigerating apparatus to which another screw compressor according to the present invention is applied.

FIG. 5 is a view schematically showing a refrigerating apparatus to which still another screw compressor according to the present invention is applied.

FIG. 6 is a flowchart showing control on a screw compressor in the refrigeration apparatus shown in FIG.

FIG. 7 is a view schematically showing a refrigerating apparatus to which still another screw compressor according to the present invention is applied.

FIG. 8 is a flowchart showing control on a screw compressor in the refrigeration apparatus shown in FIG.

FIG. 9 is a view schematically showing a refrigerating apparatus to which still another screw compressor according to the present invention is applied.

FIG. 10 is a flowchart showing control on a screw compressor in the refrigeration apparatus shown in FIG.

FIG. 11 is a view schematically showing a refrigerating apparatus to which still another screw compressor according to the present invention is applied.

FIG. 12 is a flowchart showing control on a screw compressor in the refrigeration apparatus shown in FIG.

FIG. 13 is a view schematically showing a refrigerating apparatus to which still another screw compressor according to the present invention is applied.

FIG. 14 is a flowchart showing control on a screw compressor in the refrigeration apparatus shown in FIG.

FIG. 15 is a view schematically showing a refrigerating apparatus to which still another screw compressor according to the present invention is applied.

16 is a flowchart showing control on a screw compressor in the refrigeration apparatus shown in FIG.

FIG. 17 is a diagram illustrating changes in power consumption and motor current of the compressor when the condensing temperature in the refrigeration apparatus changes.

FIG. 18 is a diagram showing a change in the motor speed of the compressor and an upper limit of the motor speed when the condensing temperature in the refrigerating device changes.

FIG. 19 is a view showing a structure in a case where the compressor of the refrigerating apparatus is an oil-cooled type.

FIG. 20 is a diagram showing a change in gas flow velocity in an oil recovery unit following an oil-cooled compressor when the condensing temperature in the refrigeration apparatus changes.

[Explanation of symbols]

 1A Screw compressor 10A Refrigeration unit 22 Motor 25 Inverter 26 Controller D1 Motor coil temperature detector D3 Suction pressure detector

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F25B 1/047 F25B 1/047 P (72) Inventor Eiji Kamiyoshi 41 Niijima, Harima-cho, Kako-gun, Hyogo Stock Shares Company Kobe Steel Harima General-purpose Compressor Factory F term (reference) 3H029 AA03 AA18 AB03 BB11 BB44 BB50 BB51 CC02 CC07 CC27 CC53 CC56 CC58 CC62 3H045 AA05 AA12 AA27 AA31 BA12 CA02 CA19 DA07 EA13 EA16 EA16

Claims (2)

[Claims] In a screw compressor for a refrigerating machine driven by a motor whose rotation speed is controlled via an inverter, a heat load detecting means for detecting a cooling heat load; At least one load state detecting means for detecting a factor, and based on a heat load signal input from the heat load detecting means, when it is determined that the compression function is excessive, the rotational speed of the motor is reduced. If it is determined that the compression function is neither excessive nor insufficient, the rotational speed of the motor is maintained, and if it is determined that the compression function is insufficient, the load state detection means A controller that reduces the rotation speed of the motor when it is determined that the load condition is excessive based on the load condition signal input from the controller, and increases the rotation speed of the motor otherwise. Preparation A screw compressor for a refrigerator. 2. The controller according to claim 1, wherein the controller determines whether the load condition is excessive when the load condition is the rotational speed of the motor. The determination is made based on whether or not the motor exceeds the upper limit rotational speed determined in accordance with the pressure.If the rotational speed exceeds the upper limit, the motor is determined to be excessive, and the rotational speed of the motor is reduced. The screw compressor for a refrigeration system according to claim 1, wherein the number of rotations is increased.