KR20070042078A - Two stage screw compressor and compression refrigerator using the same - Google Patents

Abstract

In the two-stage screw compressor of the present invention, the stroke volume ratio of the first-stage compressor and the second-stage compressor is adjusted by changing the stroke volume of the first-stage compressor and the second-stage compressor by the stroke volume varying means in accordance with the change of the suction pressure. And a capacity adjusting means for adjusting the capacity by varying the rotational speed of the motor by the rotation volume ratio adjusting means. With this configuration, the stroke volume ratio of the first and second stages is adjusted so that the intermediate pressure is an ideal value, and the burden of the compressors of the first and second stages can be reduced according to the change of the evaporation temperature, and the operation can be performed efficiently. Can be.

2-stage screw compressor, oil separator, condenser, expansion valve, evaporator, casing

Description

TWO STAGE SCREW COMPRESSOR AND COMPRESSION REFRIGERATOR USING THE SAME}

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a two stage compression freezer cycle with a two stage screw compressor according to the present invention.

FIG. 2 is an enlarged sectional view of the piston valve of the two stage screw compressor of FIG.

3 is a graph showing changes in suction pressure, intermediate pressure, and discharge pressure of a two-stage screw compressor with respect to a change in evaporation temperature.

4 is a graph showing the change in the intermediate pressure when the ideal middle pressure and the stroke volume ratio of the two-stage screw compressor are constant with respect to the change in the evaporation temperature.

<Explanation of symbols for the main parts of the drawings>

1: two stage screw compressor

2: oil separator

3: condenser

4: expansion valve

5: evaporator

6: refrigerant circulation flow path

7: 1 stage compressor

8: casing

9: drive shaft

10: two stage compressor

11: two stage compressor casing

12: motor

13: motor casing

14: suction port

15: filter

16 discharge port

17: cylinder

18: piston valve

19: gas space

20: hydraulic space

21: hole

22: coil spring

[Document 1] Japanese Unexamined Patent Application Publication No. 11-117879

[Document 2] Japanese Unexamined Patent Publication No. 2003-21089

[Document 3] Japanese Unexamined Patent Publication No. 2004-278824

The present invention relates to a two stage screw compressor and a two stage compressor using the same.

In a two-stage compressed refrigerator having a two-stage screw compressor, a condenser, an expansion valve, and an evaporator in the refrigerant circulation passage, the evaporation temperature (ET) of the refrigerant in the evaporator can correspond to a wide temperature range of -30 ° to -60 °. It is also required to correspond to this in the same refrigerator.

Conventionally, in the two-stage screw compressor as described in Japanese Patent Laid-Open No. 11-117879, a capacity control mechanism consisting of a slide valve is provided in the first stage side compressor, and partial load operation is performed by unloading the slide valve. In the two-stage screw compressor described in Japanese Patent Laid-Open No. 2003-21089, partial load operation is performed by controlling the rotation speed of the first stage compressor and the drive motor for rotating the second stage compressor. Moreover, in the refrigeration cycle apparatus of Unexamined-Japanese-Patent No. 2004-278824, it is described that the rotation speed of a low stage compressor and a high stage compressor is changed independently, and each rotation speed is increased or decreased according to a load. However, only by such partial load operation, the evaporation temperature ET of the refrigerant could not sufficiently correspond to a wide temperature range of -30 ° to -60 °.

In general, when the compression ratio of the first stage compressor and the compression ratio of the second stage compressor are equal, it becomes an ideal operation of the two stage compressor. When the suction pressure (suction pressure of the first stage compressor) is Ps, the intermediate pressure (the discharge pressure of the first stage compressor, and the suction pressure of the second stage compressor) is Pm, and the discharge pressure (the discharge pressure of the two stage compressor) is Pd, Since the first stage compression ratio r1 = Pm / Ps and the second stage compression ratio r2 = Pd / Pm, when the first stage compression ratio r1 and the second stage compression ratio r2 are equal (r1 = r2), Pm / Ps From = Pd / Pm, Pm = √ (Ps · Pd).

When the discharge pressure is 15.64 ata and the suction pressure Ps (ata) at the evaporation temperature (ET) (° C) of -30, -40, -50, or -60 is set to 1.67, 1.07, 0.658, 0.382, respectively. The median pressure Pm (ata) is 5.11, 4.09, 3.21, 2.44 from Pm = √ (Ps.Pd), which is as shown in FIG. 3 shows that when the discharge pressure and the suction pressure of the two-stage screw compressor are determined, the ideal intermediate pressure is determined when the compression ratio of the first stage compressor and the compression ratio of the second stage compressor are equal.

In practice, however, the intermediate pressure is determined by the stroke volume ratio R (= V1 / V2) which is the ratio of the stroke volumes of the first stage compressor and the second stage compressor. In addition, a stroke volume means the volume compressed per unit time in a compressor. When the cost of the compressed medium corresponding to the suction pressure Ps is set to v1 and the cost of the compressed medium corresponding to the intermediate pressure Pm is set to v2, since v1 / v2 = V1 / V2 = R, v2 = v1 × (1 V2 is obtained from / R), and the intermediate pressure Pm is obtained from the pressure corresponding to this v2. Also, cost is the volume per unit weight of the object. In addition, the "pressure equivalent to v2" here is calculated | required using the Moriel diagram (P-h diagram) etc. well known in the field of a refrigerator. For example, v1 when evaporation temperature (ET) (degreeC) is -30, -40, -50, -60 changes to 0.135, 0.205, 0323, 0.536. Using this v1 and the stroke volume ratio R = 3, the median pressure Pm is obtained, plotted in the figure, and shown in FIG. 4 together with the ideal median pressure. From Fig. 4, when the evaporation temperature is -40 deg. C, the intermediate pressure is approximately the same as the ideal intermediate pressure. However, at the evaporation temperature of -30 to -40 deg. C, the intermediate pressure is higher than the above intermediate pressure. When the evaporation temperature is -40 to -60 ℃, the intermediate pressure is lower than the above intermediate pressure, it can be seen that the burden on the two-stage compressor increases.

As described above, in the conventional two-stage screw compressor, the stroke volume ratio of the first stage compressor and the second stage compressor is constant over the evaporation temperature ET of -30 ° to -60 °. For this reason, if the design point is determined to be the optimum evaporation temperature, it becomes an ideal intermediate pressure at that point, but at other evaporation temperatures, one compressor is excessively burdened and the efficiency of the compressor is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional problems, and adjusts the stroke volume ratio of the first and second stages to make the intermediate pressure an ideal value, and reduces the burden on the compressors of the first and second stages according to the change in the evaporation temperature. Another object is to provide a two-stage screw compressor capable of efficient operation and a two-stage compressed refrigerator using the same.

In Fig. 4, in order to bring the intermediate pressure represented by the dashed-dotted line closer to the ideal intermediate pressure represented by the solid line, in the region where the evaporation temperature is -30 deg. The stroke volume ratio may be lowered to R = 0.135 / 0.053 = 2.55 so as to achieve a cost of 0.053 corresponding to the ideal medium pressure of 5.11 ata, that is, the stroke volume of the compressor on the first stage may be 2.55 / 3.0 = 0.85 (15% reduction). The resulting reduction in compression capacity is addressed by increasing the rotational speed of the screw compressor. On the other hand, in the region where the evaporation temperature is -60 deg. This makes it possible to bring the intermediate pressure closer to the ideal intermediate pressure. This invention is made | formed based on this knowledge.

That is, the present invention is a two-stage screw compressor, which drives a first stage compressor disposed in the compressor main body, a second stage compressor disposed downstream of the first stage compressor in the compressor main body, the first stage compressor, and the second stage compressor. A single motor, a stroke volume varying means for varying at least one stroke volume of the first stage compressor and the second stage compressor, a suction pressure detector for measuring the suction pressure value Ps of the first stage compressor; The stroke volume ratio adjusting means for adjusting the stroke volume ratio of the first stage compressor and the second stage compressor, the rotation control means for controlling the rotation speed of the motor, and the rotation speed of the motor by the rotation control means to change the 2 However, it consists of a capacity | capacitance adjustment means which adjusts the capacity | capacitance of a screw compressor, and the said stroke volume ratio adjustment means is the suction which was measured by the said suction pressure detector. By the stroke volume varying means according to the pressure value (Ps) thereby changing the stroke volume of the at least either one of said first end side compressor and the second short-side compressor.

In the two-stage screw compressor of the present invention, when the stroke volume ratio of the first-stage compressor and the second-stage compressor is changed by the stroke volume ratio adjusting means, the intermediate pressure changes, so that the intermediate pressure can be made close to the ideal theoretical intermediate pressure.

In addition, in the two-stage screw compressor of the present invention, since the rotation speed of the motor is changed by the capacity adjusting means, the capacity of the two-stage screw compressor, that is, the supply amount of the compressed gas can be changed. Thereby, it becomes possible to send out the quantity as required by the supply source of a compressor body.

As described above, in the present invention, by combining the stroke volume ratio adjusting means and the capacity adjusting means, a two-stage screw compressor capable of efficient operation is artfully realized. That is, the efficiency by controlling the intermediate pressure to an ideal value is in charge of the stroke volume varying means and the stroke volume ratio adjusting means, and the control of the supply amount of the compressed gas is mainly in charge of the rotation control means and the capacity adjustment means. In other words, the stroke volume varying means is used only for the optimization of the intermediate pressure, and the rotational control means is separately used for adjusting the supply amount.

The two-stage screw compressor of the present invention further comprises a discharge pressure detector for measuring the discharge pressure value Pd of the two-stage compressor and an intermediate pressure detector for measuring the intermediate pressure value Pm, which is the discharge pressure value of the first-stage compressor. The stroke volume ratio adjusting means is based on √ (Ps · Pd) based on the suction pressure value Ps measured by the suction pressure detector and the discharge pressure value Pd measured by the discharge pressure detector. The stroke volume is calculated by the stroke volume varying means such that the intermediate pressure value Pmth is calculated and the difference between the intermediate pressure value Pm measured by the intermediate pressure detector and the theoretical intermediate pressure value Pmth is zero. It is desirable to change.

The stroke volume varying means may be a piston valve or a slide valve. Although the stroke volume variable means should just be in at least one of a 1st stage compressor and a 2nd stage compressor, it is preferable to provide in a 1st stage compressor. The rotation control means may be an inverter.

In addition, the present invention is a two-stage compressed refrigerator using the two-stage screw compressor of the above configuration, the two-stage screw compressor, the condenser, the expansion valve and the evaporator are provided in this order in the refrigerant circulation passage, the evaporator measures the evaporation temperature An evaporation temperature detector is provided, and the capacity adjusting means changes the rotational speed of the motor by the rotation control means so that the difference between the evaporation temperature value measured by the evaporation temperature detector and the preset target steam temperature value becomes zero. Let's do it.

According to the two-stage compression refrigerator of the present invention, the medium pressure can be made close to the ideal theoretical medium pressure for a wide range of evaporation temperatures, and the efficiency of the compressor can be greatly improved. In particular, even when the intermediate pressure is too high to operate at -20 to -30 deg. C, it is possible to operate by adjusting the stroke volume by lowering the intermediate pressure by the stroke volume ratio adjusting means.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described according to an accompanying drawing.

1 shows a cycle of a two stage compressed refrigerator using a two stage screw compressor 1 according to the present invention. This refrigeration cycle is a two-stage screw compressor (1), oil separator (2), condenser (3), expansion valve (4) and evaporator (5) connected to the refrigerant circulation passage (6).

The main body of the two-stage screw compressor (1) includes a first stage compressor casing (8) containing a first stage compressor (7) consisting of a pair of male and female screw rotors engaged with each other, and several times of the first stage compressor (7). A two-stage compressor casing 11 having a drive shaft 9 common to the former, and having a two-stage compressor 10 composed of a pair of male and female screw rotors engaged with each other; the first-stage compressor 7 and the It consists of the motor casing 13 which accommodates the single motor 12 which drives the drive shaft 9 of the two stage side compressor 10. As shown in FIG.

The first stage compressor casing 8 is provided with a suction port 14 communicating with the suction side of the first stage compressor 7, and a filter 15 is provided upstream of the suction port 14. The discharge side of the first stage compressor 7 communicates with the suction side of the second stage compressor 10 via a space in the casing. The two stage compressor casing 11 is provided with a discharge port 16 which communicates with the discharge side of the two stage compressor 10.

As shown in Fig. 2, a cylinder 17 is formed in the first stage compressor casing 8 in parallel with the drive shaft 9 of the first stage compressor 7. A piston valve 18 is provided in the cylinder 17. It is housed so that it can slide. The piston valve 18 separates the cylinder 17 into a gas space 19 located on the suction side of the first stage compressor 7 and a hydraulic space 20 located on the discharge side of the first stage compressor 7. have. The piston valve 18 inserts one end of the coil spring 22 into the hole 21 formed in the axial direction from the gas space 19 side of the cylinder 17, and the other end of the coil spring 22 is formed into a cylinder ( By contacting the end wall of 17), it is pressed to the discharge side of the first stage compressor 7. The coil spring 22 is guided by the guide rod 23 located inside it. The gas space 19 of the cylinder 17 communicates with the suction side of the first stage compressor 7, and closes the first stage compressor 7 via a plurality of openings 24 formed in the first stage compressor casing 8. It is supposed to communicate with space. Hydraulic pressure is supplied to the hydraulic space 20 of the cylinder 17 to move the piston valve 18 to the gas space 19 side against the pressing force of the coil spring 22.

Returning to Fig. 1, the motor 12 of the two-stage compressor 10 is supplied with electric power from the power supply 25 via the inverter 26, and the rotation speed is controlled. The inverter 26 constitutes rotation control means. In addition, the hydraulic pressure is supplied to the hydraulic space 20 of the piston valve 18 by the hydraulic device 27, and the piston valve 18 opens all the openings by adjusting the supply amount of the hydraulic pressure to the hydraulic space 20. It can be set as the full load state which closed the 24, and the unload state which opened the at least 1 opening part 24. FIG. The piston valve 18 constitutes a capacity control means. The inverter 26 and the hydraulic device 27 are controlled by the controller 28. The controller 28 can input the suction pressure Ps, the intermediate pressure Pm, and the discharge pressure Pd measured by the pressure gauge. Further, the pressure gauge includes a flow path (Ps measurement) in communication with the suction side of the first stage compressor 7, a space in the casing (Pm measurement) between the discharge side of the first stage compressor 7 and the suction side of the second stage compressor 10, It is provided in the flow path (Pd measurement) which communicates with the discharge side of the two stage compressor 10, respectively. In addition, the evaporator temperature detected by the temperature sensor 29 installed in the evaporator 5 is input to the controller 28 via the temperature controller 30. The controller 28 constitutes the stroke volume ratio adjusting means and the capacity adjusting means of the present invention.

Next, the operation of the two-stage compression refrigerator having the above configuration will be described.

For example, the stroke volume ratio R (= V1 / V2) of the stroke volume V1 of the first stage compressor 7 and the stroke volume V2 of the second stage compressor 10 is designed to be R = 3. do. In this case, in the state where the stroke volume ratio between the first stage compressor 7 and the second stage compressor 10 is R = 3 in the state where the first stage compressor 7 is in full load, the intermediate pressure Pm is shown in FIG. As can be expected, it will be 6.3 ata above the theoretical median pressure Pmth. Here, when the piston valve 18 is moved and the first stage compressor 7 is unloaded 15%, the stroke volume of the first stage compressor 7 becomes 85%, and the stroke volume ratio R is R = 3 × 0.85 = 2.55. As a result, intermediate pressure Pm falls and it can be made close to theoretical intermediate pressure Pmth. In this way, the medium pressure can be made close to the ideal theoretical medium pressure Pmth for a wide range of evaporation temperatures, and the efficiency of the compressor can be greatly improved. Thus, when this two stage compressed refrigerator is designed such that the stroke volume ratio R (= V1 / V2) becomes R = 3, as can be understood from FIG. 4, the evaporation temperature ET (° C) is-. If the suction pressure is 40 ° C. or higher and the Ps is 1.07 ata or more, the intermediate pressure Pm is lowered by moving the piston valve 18 and unloading the first stage compressor 7 by the required ratio, thereby lowering the theoretical medium. It can be close to the pressure value.

In addition, setting an arbitrary amount of unloading in this way can be implemented without a problem using the mechanism shown in FIG. That is, in FIG. 2, the opening part 24 is provided so that the movement amount and unload amount of the piston valve 18 may be proportional. The unloading mechanism by such a piston valve is known.

In the two-stage screw compressor 1 of FIG. 1, since a pressure gauge for measuring the suction pressure Ps, the discharge pressure Pd, and the intermediate pressure Pm is provided, the two-stage screw compressor 1 in an operating state is provided. When the suction pressure Ps, the discharge pressure Pd, and the intermediate pressure Pm measured in the above are input to the controller 28, the controller 28 inputs the theoretical intermediate pressure Pmth = √ (Ps · Pd). The piston valve 18 is moved so that the difference between the measured intermediate pressure Pm and the theoretical intermediate pressure Pmth is zero. Here, the moving position of the piston valve 18 may be determined by PID calculation based on the measured intermediate pressure Pm and the theoretical intermediate pressure Pmth.

The pressure gauge of the discharge pressure Pd may be omitted when the use of the discharge pressure Pd becomes substantially constant, for example, when the two-stage screw compressor 1 is applied to the refrigerator. In this case, the discharge pressure value may be stored in the controller 28 and used for the calculation of the theoretical intermediate pressure Pmth.

In addition, when discharge pressure Pd is substantially constant, the pressure gauge of intermediate pressure Pm may be abbreviate | omitted, and the position of the piston valve 18 may be determined only according to the value of suction pressure Ps. That is, the relationship between the value of the suction pressure Ps and the position of the piston valve 18 whose intermediate pressure Pm becomes approximately the theoretical intermediate pressure Pmth in the value of the suction pressure Ps is calculated | required beforehand, The relationship is stored in the controller 28. In operation, the position of the piston valve 18 is determined based on the measured discharge pressure Pd based on the stored relationship.

On the other hand, the evaporation temperature detected by the temperature sensor 29 in the evaporator 5 is input to the temperature controller 30, the temperature controller 30 compares the detected evaporation temperature with the target temperature, when it is higher than the target temperature The controller 28 requires an increase in speed. As a result, the controller 28 increases the rotation speed of the motor 12 via the inverter 26. As a result, the stroke volume of the 1st stage compressor 7 and the 2nd stage compressor 10 becomes large simultaneously, and capacity | capacitance and the freezing capacity can be enlarged, maintaining the stroke volume ratio R in an ideal state. On the contrary, when it is lower than the target temperature, the rotation speed of the motor 12 is reduced, and loss of excessive cooling or the like is prevented.

In the two-stage compression refrigerator having the above-described configuration, the evaporation temperature ET (° C) is higher than or equal to a predetermined temperature (specifically, -40 ° C), and the suction pressure Ps is higher than or equal to a predetermined pressure (specifically, 1.07 ata). In this case, the intermediate pressure Pm can be made close to the theoretical intermediate pressure Pmth. However, it is preferable that the equivalent effect is also obtained in other cases. To this end, in addition to the above-described configuration, a cylinder is formed in the two-stage compressor casing 11 in parallel with the drive shaft 9 (common with the drive shaft 9 of the first-stage compressor 7). And a piston valve separate from the piston valve 18 is housed in the cylinder so as to be slidable. In the two stage compressed refrigerator according to this configuration, not only the rinse volume of the first stage compressor 7 but also the stroke volume of the second stage compressor 10 can be changed. And if it is a two stage compression refrigerator which concerns on this structure, when it is lower than -40 degreeC, and also the suction pressure Ps is lower than 1.07 ata, the piston valve of the two stage compressor 10 side will be moved, and the two stage compressor will be moved. By unloading (10) by the required ratio, it is possible to raise the intermediate pressure Pm and bring it closer to the theoretical intermediate pressure Pmth.

In addition, although the piston valve 18 was used as a stroke volume variable in the said Example, a slide valve may be used. In addition, the piston valve 18 and the slide valve are not limited to the 1st stage compressor 7 as mentioned above, but may be provided in the 2nd stage compressor 10, and the 1st stage compressor 7 and the 2nd stage compressor 10 are mentioned. May be formed on both sides.

According to the present invention, the stroke volume ratio of the first and second stages is adjusted to make the intermediate pressure an ideal value, and the burden of the compressors of the first and second stages can be reduced according to the change of the evaporation temperature, and efficient operation can be performed. It is possible to provide a two-stage screw compressor and a two-stage compression refrigerator using the same.

Claims (6)

Two stage screw compressor, A first stage compressor disposed in the compressor main body, A two stage compressor disposed downstream of the first stage compressor in the compressor body; A single motor for driving the first stage compressor and the second stage compressor; A stroke volume varying means for varying at least one stroke volume of the first stage compressor and the second stage compressor; A suction pressure detector for measuring a suction pressure value Ps of the first stage compressor; A stroke volume ratio adjusting means for adjusting the stroke volume ratio of the first stage compressor and the second stage compressor; Rotation control means for controlling the rotation speed of the motor; It is made of a capacity adjusting means for adjusting the capacity of the two-stage screw compressor by changing the rotational speed of the motor by the rotation control means, The stroke volume ratio adjusting means includes two stages of changing at least one stroke volume of the first stage compressor and the second stage compressor by the stroke volume varying means in accordance with the suction pressure value Ps measured by the suction pressure detector. Screw compressor. The pressure gauge according to claim 1, further comprising a discharge pressure detector for measuring the discharge pressure value Pd of the two-stage compressor, and an intermediate pressure detector for measuring the intermediate pressure value Pm, which is the discharge pressure value of the first-stage compressor, The stroke volume ratio adjusting means is theoretically intermediate by √ (Ps · Pd) based on the suction pressure value Ps measured by the suction pressure detector and the discharge pressure value Pd measured by the discharge pressure detector. The pressure value Pmth is calculated and the stroke volume is changed by the stroke volume varying means such that the difference between the intermediate pressure value Pm measured by the intermediate pressure detector and the theoretical intermediate pressure value Pmth becomes zero. Two stage screw compressor. The two-stage screw compressor according to claim 1, wherein the stroke volume varying means is a piston valve. The two-stage screw compressor according to claim 1, wherein said stroke volume varying means is a slide valve. The two-stage screw compressor of claim 1, wherein the rotation control means is an inverter. It is a two stage compression refrigerator using the two stage screw compressor of Claim 1, In the refrigerant circulation passage, the two-stage screw compressor, the condenser, the expansion valve, and the evaporator according to claim 1 are provided in this order, The evaporator is provided with an evaporation temperature detector for measuring the evaporation temperature value, The capacity adjusting means includes a two-stage screw compressor for changing the rotational speed of the motor by the rotation control means so that the difference between the evaporation temperature value measured by the evaporation temperature detector and the preset target steam temperature value becomes zero. Used two stage compression freezer.

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