JPH03185293A - Displacement compressor rotating screw - Google Patents

Abstract

PURPOSE:To prevent an abnormal rise in the inner pressure of a high-stage machine in a compressor where a bypass valve for returning gas to a lower position during compression is installed in the high-stage machine by detecting low or intermittent pressure, and performing control of opening the bypass valve when the detected value is larger than a set value. CONSTITUTION:In a refrigerating cycle including a two-stage screw compressor a mixture of refrigerant gas and oil delivered from the high-stage casing 4 of the two-stage screw compressor is allowed to pass through a condensor 29 and an evaporator 30 after separation of the oil therefrom by an oil separator 27 and is then introduced into the low-stage casing 1 of the compressor through an inlet gas strainer 31. A bypass hole 16 is formed through the high-stage casing 4 in such a manner as being perpendicular to the direction of a rotor shaft and refrigerant is introduced into a high-stage suction opening through a spindle 18 forming a bypass valve and through another bypass hole 17 while the refrigerant is compressed in the compressor. In this case the spindle 18 is so controlled that when temperature is high inside a refrigerator and low pressure is more than a set value a spring 19 forces the spindle to open.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to measures for improving the reliability of a two-stage compression refrigerator using a positive displacement compressor such as a screw.

[Conventional technology]

Conventional two-stage compressors are refrigeration VoQ, 63. Na731゜1
As shown in Figure 2 on page 46 of 988-9, a slide valve is attached to the low stage machine to control the capacity, but no consideration is given to the high stage side.

Therefore, in Japanese Patent Application No. 63-102531, an attempt was made to attach a bypass valve on the high stage side to reduce the load at startup.

This load reduction is highly effective and is widely used in current compound two-stage refrigerators.

[Problem to be solved by the invention]

The present invention is an effective improvement in a two-stage compressor in order to solve problems under the special conditions of a two-stage refrigerator.

The usable evaporation temperature of a two-stage refrigerator is -30°C.
It has a wide range from -70°C to -70°C. On the other hand, when starting up, for example, when the warehouse is empty, it will be cooled down from room temperature, and when a room-temperature cargo arrives, the temperature inside the warehouse will rise to near room temperature even if the warehouse is cold. It will then rapidly cool down to freezing temperatures. Furthermore, removing frost from a heat exchanger that has reached a low temperature is an essential condition that cannot be avoided in a refrigerator.

In such cases, (1) pulldown from normal temperature, (2) rapid freezing and cooling, and (3) defrosting, unlike normal conditions, the suction pressure suddenly rises and must be lowered from a high pressure.

When the suction pressure rises rapidly in this manner, the discharge pressure on the lower stage side, that is, the intermediate pressure increases, as a characteristic of the two-stage cold kneader. This intermediate pressure is the suction pressure on the high stage side, and the high stage machine compresses in this state. As is well known, displacement machines such as screws have open discharge valves, so internal compression is performed up to the pressure determined by the set volume ratio, regardless of the discharge pressure. This is also related to the set volume ratio, but for example, if suction pressure is 2.5 ata (evaporation temperature of about -20°C), the intermediate pressure will be 8.5 ata, and the internal pressure of the high stage machine will be 28 ata.
It will also reach ta. This increase in internal pressure acts directly on the screw rotor as a lateral load, increasing the load on the bearings that support the screw rotor, causing a loss of life.

Furthermore, if the pressure rise is large, the difference between the suction pressure and the suction pressure increases, causing abnormal vibrations due to increased gas flow noise and pressure fluctuations due to gas leakage.

In order to prevent this, conventional methods have been used to lower the suction pressure by attaching a suction pressure regulating valve, but this has the disadvantage of being disadvantageous in terms of cost and the resistance of the regulating valve resulting in unavoidable losses during normal operation. be.

Therefore, a system that minimizes losses and suppresses pressure rise is required.

[Means to solve the problem]

In order to achieve this objective, 1. During normal operation, the compressed gas of the high stage machine is bypassed to avoid overcompression when starting quick freezing or switching to hot gas defrost, which increases PS, without any extra operations. It is most effective to do so. This method is the simplest and most reliable.

That is, overcompression can be prevented by opening and closing a bypass valve attached to a high-stage machine by detecting low or medium pressure. This may be medium pressure detection or low pressure detection. If the design specifications of the compressor are clear, medium pressure is better, but low pressure can be sufficient if an allowable range is provided. In addition,
To close this bypass valve, it is best to send a signal by lowering the low pressure, by using a timer, etc.

[Effect]

During normal operation, hydraulic pressure acts on the back of the spindle to close the bypass hole and continue normal operation.

For example, when the low pressure is high due to defrosting, by lowering the pressure on the back of this spindle, the spindle opens and the bypass hole communicates with the intermediate pressure section, and the gas that is being compressed is bypassed to the intermediate pressure section and the pressure does not rise. Therefore, the overcompression state is suppressed and the bearing load is reduced.

The increase in pressure depending on the presence or absence of a bypass goes from 8.5 ata to 28 ata without a bypass, but stops at 13 ata with a bypass.

That is, for the bearing load when increasing the pressure from 8.5 ata to 28 ata, 8,5 ata → 13
ata, and the bearing load is significantly reduced.

〔Example〕

The first engineering drawing is a cycle configuration diagram including the compressor, and the second diagram is a detailed diagram of the bypass spindle section.

Oil separator 27 as a refrigeration cycle including a two-stage screw compressor. Oil cooler 28. Capacitor 29.
Evaporator 30. It consists of a suction gas strainer 31.

The oil also passes through an oil strainer 32.

The operation of this refrigeration cycle will be explained. Refrigerant gas and oil discharged from the compressor are separated by an oil separator 27, and the refrigerant flows to a condenser 29, an evaporator 30, and returns to the compressor via a suction gas strainer 31.

The oil separated by the oil separator 27 is transferred to the oil cooler 28.
After being cooled down to an appropriate temperature, the oil is supplied to the bearings and the spindle back pressure of the starting unloader mechanism, which will be described later, through the oil strainer 32. From oil separator 27 to capacitor 29
．． The oil cooler 28° oil strainer 32 is always under high pressure during operation.

Next, the structure of the compressor will be explained.

The main components of a two-stage screw compressor are the lower stage casing1. High stage casing 4, rotor 2, 3°5.6 and motor casing 8. They are a motor 7 and bearings 11-15. 9 is a gas inlet, and 10 is a gas outlet.

That is, the rotors 2 and 3 are housed in the casing, and are supported by bearings ↓1 and 12, respectively. Rotors 5 and 6 are housed in the high-stage casing 4, and bearings 14 and 15 support each rotor. The motor 7 is housed in a motor casing 8 and is disposed between the low stage and the high stage.

13 is a bearing that supports the shaft of the motor 7. The shafts of the low and high stages are directly connected via a joint 33.

A bypass hole 16 is provided in the high stage casing 4 so as to be orthogonal to the direction of the rotor axis. The details are shown in FIG.

This bypass hole 16 communicates with another bypass hole (7) in the rotor axial direction.

One end of the bypass hole 16 opens during compression of the casing, and the other end of the bypass hole 17 communicates with a high-stage suction port (that is, an intermediate pressure for a two-stage machine).

A spindle 18 is fitted into the bypass hole 16, and the outside thereof is closed with a cover.

The spindle 18 has three diameter stages, the small diameter part fits into the bypass hole 16, and the middle diameter part fits into the spring 19. The large diameter portion is fitted into the large diameter portion of the bypass hole 16 . The stepped portion 21 between the small diameter portion and the medium diameter portion is a bypass hole 16.
It has a structure that perfectly fits the step 20 between the small diameter part and the large diameter part. The spring 19 is a compression spring, and in its free state opens the spindle 18 from the bypass hole 16.

A cover 22 is provided on the back of the spindle 18, and the spindle 18 is connected to an oil supply and drainage pipe via the cover 22. The oil supply and drain pipes each have one end connected to high pressure oil and the other end connected to a low pressure gas section via on-off valves 23 and 24, respectively.

Next, the operation of the two-stage screw compressor having the above structure will be explained.

For example, when the temperature inside the refrigerator is high and the low pressure is high, the low pressure or
When intermediate pressure is detected, valve 23 closes and valve 24 opens.

In this state, the back pressure on the spindle becomes low. Spring 19 stretches to open spindle 18. That is, the bypass hole 16 opens and communicates with the bypass hole 17, allowing communication between the inside of the casing and the suction side. That is, the pressure increase in the compressed gas caused by the rotation of the rotor is partially released to the suction side, thereby preventing an increase in internal pressure. During normal operation, valve 23 is opened and valve 24 is closed. In this state, the back pressure of the spindle 18 cuts off the low pressure and supplies the high pressure via the hydraulic source 25.

That is, high pressure is applied to the large diameter part as a back pressure of the spindle, and since the small diameter part has an intermediate pressure, the spindle is pressed into the bypass hole of the casing due to the high pressure, the bypass holes 6 and 17 are cut off, and the compression is stopped during compression. It is completely occluded and becomes a regular casing, resulting in normal compression.

The opening and closing operations of the valves 23 and 24 are controlled proportionally to a set value by detecting either low pressure or intermediate pressure.

Note that in order to form a normal operation pattern in which the valve 23 is closed and the valve 24 is opened, detection of a drop in the low pressure, timer control, or a combination of both can be considered.

〔Effect of the invention〕

According to the invention, (1) Abnormal rise in internal pressure of the high stage machine can be prevented.

(2) By (1), it is possible to prevent abnormal noise and abnormal vibration from occurring due to internal pressure increase.

(3) The overcompression pulsation noise due to (1) can be reduced.

(4) It is possible to reduce the bearing load due to (1) and thereby extend the bearing life.

[Brief explanation of drawings]

FIG. 1 is a cycle system diagram including a compressor according to an embodiment of the present invention, and FIG. 2 is a detailed explanatory diagram of a spindle. 5.6...-〇-7Cfl Jiq no Takuzu

Claims (1)

[Claims] 1. Detecting low pressure or intermediate pressure in a rotary displacement machine such as a screw, which is equipped with a bypass valve in a high-stage machine that can return at least gas in the middle of compression to a lower position including intermediate pressure. A rotary displacement machine such as a screw, characterized in that when this value is larger than a set value, a bypass valve is opened.