JP2001263837A - Refrigerating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigerating circuit capable of improving reliability by rapidly and surely recovering a lubricating oil stored in a refrigerant circuit to a compressor and extending a lifetime of the compressor. SOLUTION: A sensor (13) for sensing a temperature of a refrigerant gas from a screw compressor (2) is provided in the refrigerating circuit (1) for sequentially connecting the compressor (2), a condenser (3), an expansion valve (4) and an evaporator (5) via piping (6a to 6d) to circulate a refrigerant containing a lubricating oil. A superheat degree of the discharged refrigerant gas is calculated based on a sensing signal from the sensor (13) by a controller (14). Thus, when the calculated superheat degree is larger than a predetermined value, a slide valve (7) provided at a by-pass passage for communicating with a discharge port (2a) of the compressor (2) through a suction port (2b) is closed to an opening degree corresponding to a 80%-full load for 10 s. Then, a refrigerant circulating amount is increased to recover the oil to the compressor (2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refrigeration circuit having means for recovering lubricating oil contained in a refrigerant circulating in a refrigeration circuit to a screw compressor which is a component of the refrigeration circuit.

[0002]

2. Description of the Related Art Conventionally, as an oil return control device of a refrigerator for recovering lubricating oil contained in a refrigerant to a compressor, for example, one described in Japanese Utility Model Laid-Open No. 1-167555 is known.
This control device supplies the superheat degree of the discharged refrigerant gas (saturated refrigerant vapor having the same pressure as the temperature of the discharged refrigerant gas) to the discharge pipe of the refrigeration circuit in which the compressor, condenser, expansion valve, evaporator, and accumulator are sequentially connected by piping. A superheat controller for detecting a temperature difference from a saturation temperature corresponding to the above is provided, and two solenoid valves are interposed in parallel in an oil return pipe connecting the bottom of the accumulator and the suction pipe. When the degree of superheat indicated by the detection signal from the superheat degree controller is larger than a predetermined value, the control means opens both the solenoid valves to return a large amount of lubricating oil accumulated in the accumulator to the refrigeration circuit, Is smaller than a predetermined value, only one of the solenoid valves is opened to return a small amount of the stored lubricating oil to the refrigeration circuit.

[0003]

However, in the above-mentioned conventional refrigeration circuit, the degree of superheat of the discharged refrigerant gas may exceed the above-mentioned predetermined value and become excessive, for example, 30 ° C., in which case,
It was found that even when the two solenoid valves were fully opened, the lubricating oil did not sufficiently return from the accumulator to the refrigeration circuit. This is because if the degree of superheat of the discharged refrigerant gas rises above the limit due to some reason in the refrigeration circuit, the return of the lubricating oil will decrease and the seal of the compression sliding part of the compressor will be incomplete, and the compression efficiency will decrease. As a result, it is considered that the temperature of the discharged refrigerant gas increases more and more. This phenomenon of insufficient oil return becomes remarkable when a so-called liquid-fill type evaporator is used as the evaporator in the preceding stage of the accumulator. In particular, in the case of a part load (partial load), the amount of suction air decreases, and the amount of circulation of the refrigerant decreases, so that it becomes difficult for oil to return. If the compressor is continuously operated in such a state of running out of oil, the compression sliding part and the bearing of the screw rotor will be damaged,
Failure to operate can result in costly and time consuming repairs.

[0004] Therefore, an object of the present invention is to make it possible to quickly and reliably return the lubricating oil contained in the refrigerant accumulated in the refrigerant circuit to the compressor when the degree of superheat of the discharged refrigerant gas is excessive.
It is an object of the present invention to provide a refrigeration circuit that can extend the life of sliding portions and bearings of a compressor and improve the reliability of the compressor.

[0005]

Means for Solving the Problems The inventors of the present invention have intensively tested and studied the relationship between the degree of superheat of the discharged refrigerant gas and running out of oil in a refrigeration circuit having a liquid-filled evaporator and a screw compressor. There is a correlation, when the degree of superheat is excessive, when the slide valve provided in the bypass path communicating the suction port and the discharge port of the screw compressor is closed to a predetermined opening degree, the lubricating oil returns to the screw compressor. And found that the present invention has been accomplished.

That is, the invention according to claim 1 provides a refrigeration circuit in which a screw compressor, a condenser, an expansion mechanism, and an evaporator are sequentially connected by piping to circulate a refrigerant containing lubricating oil.
A sensor that detects the temperature of the refrigerant gas discharged from the screw compressor, and based on a detection signal from the sensor, calculates the degree of superheat of the discharged refrigerant gas, and when the calculated degree of superheat is greater than a predetermined value, A control unit that closes a slide valve provided in a bypass path communicating the suction port and the discharge port of the compressor to a predetermined opening degree and increases the amount of circulating refrigerant to collect the lubricating oil in the screw compressor is provided. It is characterized by.

In the refrigeration circuit of the present invention, the temperature of the refrigerant gas discharged from the screw compressor is detected by a sensor, and a detection signal is sent to the control unit. The control unit calculates the degree of superheat of the discharged refrigerant gas based on the detection signal, and if the calculated degree of superheat is greater than a predetermined value, determines that oil has run out and communicates the suction port and the discharge port of the screw compressor. The slide valve provided in the bypass is closed to a predetermined opening. Then, the amount of refrigerant bypassing from the discharge port of the screw compressor to the suction port is reduced, and the amount of refrigerant circulating in the refrigeration circuit is increased.Therefore, the lubricating oil accumulated in the refrigerant circuit together with the refrigerant having increased circulation amount is compressed by the screw. Come back to the machine. The sliding parts and bearings of the screw compressor are completely sealed by the returned lubricating oil, which restores compression efficiency and reduces the temperature of the discharged refrigerant gas to an appropriate degree of superheat, eliminating damage to bearings and the like. The service life of the screw compressor is prolonged, good operation can be maintained, and the reliability of the screw compressor is improved.

In the refrigeration circuit according to the present invention, after the control section maintains the opening degree of the slide valve closed to the predetermined opening degree for a predetermined time, the control section responds to the degree of superheat of the discharged refrigerant gas. And closing and opening the slide valve.

In the refrigeration circuit according to the second aspect, since the control unit maintains the predetermined opening of the slide valve closed at the time of oil return for a predetermined time, a sufficient amount of lubricating oil is recovered in the screw compressor during that time. Therefore, the sliding parts and bearings of the screw compressor are more completely sealed, the life of the screw compressor is further extended, and the reliability is further improved. Subsequently, the control unit closes and opens the slide valve according to the degree of superheat of the discharged refrigerant gas which increases or decreases according to the magnitude of the refrigeration load, so that the refrigerant circulation amount of the refrigeration circuit increases or decreases. Then, the temperature of the liquid to be cooled coming out of the evaporator is controlled to the target value, and immediately after the oil return as the forced load-up control is completed, the control can immediately proceed to the superheat degree control as the normal temperature control.

The refrigeration circuit according to a third aspect of the present invention is characterized in that the evaporator is a full-type evaporator in which a liquid to be cooled flows in a pipe provided in a casing and a refrigerant flows in the casing. .

In the refrigeration circuit of the third aspect, since the evaporator is of a liquid-fill type in which lubricating oil heavier than the refrigerant accumulates at the bottom of the casing, the oil cannot be returned by the conventional method from the accumulator. By the forced load-up control for closing the slide valve of the compressor to a predetermined opening, the lubricating oil collected at the bottom of the evaporator together with the refrigerant whose circulation amount increases returns to the screw compressor. Therefore,
Even with a liquid-filled evaporator that is difficult to return oil, lubricating oil that has returned in a sufficient amount eliminates damage to bearings and the like, extending the life of the screw compressor and maintaining good operation. The reliability of the compressor is improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is a diagram showing an example of a refrigeration circuit having a control unit for oil return according to the present invention. The refrigeration circuit 1 includes a screw compressor 2, a condenser 3, an expansion mechanism 4, and an evaporator 5. Pipes 6a to 6d are sequentially connected to circulate a refrigerant (for example, R134a) containing lubricating oil in the circuit. The screw compressor 2 rotates the screw rotor by a motor while meshing a gear-shaped gate rotor that is vertically provided in a groove of the screw rotor provided horizontally in the casing, and compresses the refrigerant sucked from the suction port 2b. From the discharge port 2a. The bypass passage (not shown) connecting the discharge port 2a and the suction port 2b of the screw compressor 2 includes:
A slide valve 7 is provided, which is opened from the fully closed position on the right end to the fully open position on the left end to an arbitrary degree, thereby allowing a part of the refrigerant on the compression side to escape to the suction side, thereby causing the refrigerant in the refrigerant circuit to move. The amount of circulation is reduced, and the refrigerating capacity is reduced from 100% to a ratio corresponding to the above opening.

The evaporator 5 is of a so-called full type, as shown in a detailed sectional view in FIG. 2, and the refrigerant flowing from the inlet 8b at the bottom as shown by the arrow flows upward through the casing 8 toward the outlet 8a at the top. While evaporating, the liquid to be cooled (for example, water) flowing in the pipes 9 arranged in the casing 8 in the longitudinal direction is cooled by heat exchange. Reference numeral 11 denotes a liquid-phase refrigerant accumulated in a lower portion of the casing 8. Reference numeral 10 denotes a demister for separating the refrigerant liquid mixed with the refrigerant vapor. The liquid to be cooled flowing in the pipe 9 enters and exits the evaporator 5 as shown by the arrow in FIG. The condenser 3 is provided with a cooling liquid flowing in and out as indicated by an arrow in FIG.
The refrigerant gas is cooled and liquefied by (for example, water).

The inventors of the present invention have conducted tests and studies on the relationship between the degree of superheat of the discharged refrigerant gas and running out of oil in a refrigeration circuit having a liquid-filled evaporator and a screw compressor as described above. Was closely related to the fact that when the degree of superheat was excessive, when the slide valve of the screw compressor was closed to a predetermined opening, lubricating oil was returned to the screw compressor. Therefore, a sensor 1 for detecting the temperature of the discharged refrigerant gas is provided to a pipe 6a near the discharge port 2a of the screw compressor 2.
3 and calculate the degree of superheat of the discharged refrigerant gas (the temperature difference between the temperature of the discharged refrigerant gas and the saturated temperature corresponding to the saturated refrigerant vapor having the same pressure) based on the detection signal from the sensor 13. When the superheat degree is larger than a predetermined value, a control unit 14 for performing a forced load-up control for increasing the refrigerant circulation amount of the refrigeration circuit 1 by closing the slide valve 7 to a predetermined opening degree is provided.

As shown in FIG. 3, the control of the opening and closing of the slide valve 7 of the screw compressor 2 by the control unit 14 includes two subroutines, namely, a superheat degree control in step S1 and a forced load-up control in step S2. The superheat degree control subroutine is as shown in FIG.
When the motor is switched from the star connection to the delta connection and the start is completed (S11), it is determined whether or not the flag A indicating the forced load-up control is off (S12). While determining whether or not (S
13) If it is on, the process jumps to step S2 in FIG. 3 and the subroutine of the forced load-up control shown in FIG.
If the control unit 14 determines that the degree of superheat is appropriate in step S13 in FIG. 4, the control unit 14 closes and opens the slide valve 7 so that the temperature of the liquid to be cooled which is cooled by the evaporator 5 and reaches the target value. To increase or decrease the amount of circulating refrigerant in the refrigeration circuit 1
While performing the down control (S14), if the superheat degree is less than 6 ° C. and the refrigerant circulation amount is excessive, the load control is performed to gradually open the slide valve 7 (S15, S16). If the temperature is lower than 0 ° C., the slide valve 7 is stopped at that position in order to maintain the refrigerant circulation amount at that time, and the load holding control is performed (S17).

On the other hand, in the forced load-up control subroutine, as shown in FIG. 5, when it is confirmed that the motor start of the screw compressor 2 has been completed (S21), it is determined whether the degree of superheat is too large to cause oil shortage, that is, exceeds 30 ° C. Is determined (S2
2) If it is too long, start measuring 30 minutes with the delay timer
(S23) If the excessive degree of superheat continues until the end of the timing, the flag A indicating that the forced load-up is necessary is turned on (S24 to S26). Next, the control unit 14
When it is confirmed that the flag A is ON (S27), it is determined whether or not the slide valve 7 is closed beyond substantially full closing corresponding to 80% full load (S29). Perform load-up control that gradually closes
(S28) If the result is affirmative, while keeping the opening of the slide valve at that time (S32), the detection timer starts measuring 10 seconds (S30), and the slide valve is fully loaded 80% until the end of the time measurement. If it is closed beyond
Assuming that a sufficient amount of lubricating oil has returned to the screw compressor 2, the flag A is turned off (S33), and the forced load-up control ends.

The control of the opening and closing of the slide valve 7 by the control unit 14 eliminates running out of oil in the screw compressor 2 as follows. When the superheat degree of the discharged refrigerant gas calculated based on the detection signal of the sensor 13 is in the appropriate range of 9 to 30 ° C., the evaporator 5 is controlled by the subheat control subroutine described in step S1 of FIG. 3 and FIG. The superheat degree of the discharged refrigerant gas increases or decreases in accordance with the increase or decrease of the refrigeration load determined by the conditions of the liquid to be cooled flowing through the condenser 3 or the cooling liquid flowing through the condenser 3. In order to eliminate the fluctuation, the slide valve 7 is closed and opened in step S14 in FIG. 4 to increase or decrease the amount of circulating refrigerant, so that the liquid to be cooled is cooled to the target temperature,
The screw compressor 2 does not run out of oil. When the superheat degree of the discharged refrigerant gas is 6 to 9 ° C., the control unit 14 determines that the refrigerant circulation amount is large for the low refrigerating capacity operation and holds the slide valve 7 in steps S15 and S17 in FIG. When the degree of superheat is lower than 6 ° C., the slide valve 7 is gradually opened in step S16 to gradually reduce the refrigerant circulation amount. Therefore, also in this case, the liquid to be cooled is cooled to the target temperature, and the screw compressor 2 does not run out of oil.

Next, if the lubricating oil does not sufficiently return to the screw compressor 2 due to a sudden increase in the refrigerating load and the sealing of the sliding portion is incomplete, the temperature of the discharged refrigerant gas sharply rises due to a decrease in compression efficiency. The degree of superheat may exceed 30 ° C.
Then, the control unit 14 determines in step S2 in FIG.
By the subroutine of forced load-up control described in
After measuring the time of 30 minutes in step S23 via step S22 in FIG. 5 and the superheat degree excessive state continues until the time measurement ends,
In steps S28 and S29, the slide valve 7 is closed to the almost fully closed position at 80% full load, and the state is changed to step S
Hold for 10 seconds at 30 to S32. As a result, the amount of refrigerant escaping from the discharge side of the screw compressor 2 to the suction side decreases, and the amount of refrigerant circulating in the refrigeration circuit 1 increases rapidly. The lubricating oil returns to the screw compressor 2 together with the circulating refrigerant that has rapidly increased. In the screw compressor 2, since the sliding portion and the bearing are completely sealed by the returned sufficient amount of the lubricating oil, the compression efficiency is restored, and the temperature of the discharged refrigerant gas decreases until the temperature of the discharged refrigerant gas reaches an appropriate degree of superheating. . Therefore, the screw compressor 2 is free from wear and damage of the sliding parts and bearings, and its life is extended, and good operation can be maintained and reliability can be improved.

After maintaining the 80% full load state for 10 seconds, the control unit 14 turns off the flag A in step S33, and the operation shifts to the superheat degree control subroutine in FIG. Therefore, when a sufficient amount of lubricating oil is returned to the screw compressor 2 in a short time, the temperature of the liquid to be cooled is controlled so as to be equal to the target value by increasing or decreasing the refrigerant circulation amount.
There is an advantage that control waste is eliminated. Unlike the conventional method of returning lubricating oil from the accumulator, the forced load-up control by the control unit 14 increases the amount of refrigerant circulating in the refrigeration circuit 1 rapidly and compresses the lubricating oil remaining in the refrigeration circuit together with screw compression. This is a method of returning to the machine 2. Therefore, even when the liquid replenishment type evaporator 5 described with reference to FIG. 2 is used in the refrigeration circuit 1, it is difficult to return the lubricating oil collected at the bottom of the evaporator 5 to the screw compressor 2. , And the life of the screw compressor 2 can be extended and the reliability can be improved.

The evaporator according to the present invention is not limited to the liquid-fill type evaporator of the above-described embodiment, and a refrigerant flows in a large number of pipes provided in a casing, and a liquid to be cooled flows in the casing. It may be of the form. The condenser 3 in FIG.
Either a flooded type or a normal type may be used.

[0021]

As is apparent from the above description, claim 1
The invention relates to a refrigeration circuit in which a screw compressor, a condenser, an expansion mechanism, and an evaporator are sequentially connected by piping to circulate a refrigerant containing lubricating oil, and detects a temperature of a refrigerant gas discharged from the screw compressor. Based on the detection signal from the sensor to calculate the degree of superheat of the refrigerant gas discharged,
When the calculated degree of superheat is greater than a predetermined value, a slide valve provided in a bypass which communicates the suction port and the discharge port of the screw compressor is closed to a predetermined opening degree, and the amount of refrigerant circulated is increased by increasing the refrigerant circulation amount. When the superheat degree of the discharged refrigerant gas is larger than a predetermined value, the slide valve is closed to a predetermined opening degree, and the refrigerant that escapes from the discharge side to the suction side of the screw compressor is provided. The amount of refrigerant circulating in the refrigeration circuit decreases, and the amount of lubricating oil accumulated in the evaporator of the refrigerant circuit and the like along with the increased circulating refrigerant returns to the screw compressor. The sliding parts and bearings of the machine are completely sealed, and as a result, the compression efficiency is restored,
The discharged refrigerant gas has an appropriate degree of superheating, and bearings and the like are not damaged, so that the life of the screw compressor can be extended and the reliability can be improved.

In the refrigeration circuit according to the present invention, the control unit maintains the opening of the slide valve closed to the predetermined opening for a predetermined time, and then responds to the degree of superheat of the discharged refrigerant gas. Since the slide valve is closed and opened, a sufficient amount of lubricating oil is collected in the screw compressor while maintaining the slide valve at a predetermined opening degree for a predetermined time. The slide valve is closed and opened according to the increase or decrease, so that after returning oil by the forced load-up control, it is possible to immediately shift to normal superheat control, eliminating waste of control and extending the life and reliability of the screw compressor. The performance can be further improved.

In the refrigeration circuit according to the third aspect, the evaporator is a full-type evaporator in which the liquid to be cooled flows in the pipe provided in the casing and the refrigerant flows in the casing. Even in a liquid-filled evaporator where lubricating oil accumulates at the bottom of the casing and is difficult to recover using conventional oil return methods, a sufficient amount of lubricating oil can be collected in the screw compressor, and the life of the screw compressor Extension and improvement of reliability can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a refrigeration circuit including a control unit for oil return according to the present invention.

FIG. 2 is a detailed sectional view of the liquid-filled evaporator of FIG.

FIG. 3 is a flowchart showing a control flow of a control unit in FIG. 1;

FIG. 4 is a flowchart showing a superheat degree control subroutine of FIG. 3;

FIG. 5 is a flowchart showing a forced load-up control subroutine of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refrigeration circuit 2 Screw compressor 3 Condenser 4 Expansion valve 5 Evaporator 6a-6d Pipe line 7 Slide valve 8 Casing 9 Pipe 10 Demister 11 Refrigerant 12 Lubricating oil

Claims (3)

[Claims] 1. A screw compressor (2), a condenser (3), an expansion mechanism (4), and an evaporator (5) are sequentially connected by pipes (6a to 6d) to circulate a refrigerant containing lubricating oil. In the refrigeration circuit (1), a sensor (13) for detecting the temperature of the refrigerant gas discharged from the screw compressor (2), and the degree of superheat of the discharged refrigerant gas is determined based on a detection signal from the sensor (13). When the calculated degree of superheat is larger than a predetermined value, a slide valve (7) provided in a bypass passage communicating the suction port (2b) and the discharge port (2a) of the screw compressor (2) is set to a predetermined value. A refrigeration circuit comprising: a control unit (14) that closes to an opening and increases the amount of circulating refrigerant to recover the lubricating oil to a screw compressor (2). 2. The refrigeration circuit (1) according to claim 1, wherein the control unit (14) maintains the opening of the slide valve (7) closed to the predetermined opening for a predetermined time, A refrigeration circuit, wherein the slide valve (7) is closed and opened according to the degree of superheat of the discharged refrigerant gas. 3. The refrigeration circuit according to claim 1, wherein the evaporator (5) allows the liquid to be cooled to flow through a pipe (9) provided in the casing (8). Refrigerant inside
A refrigeration circuit characterized by being a liquid-filled evaporator (5) through which (11) flows.