JPH01219372A - Equalized oiling control method for refrigerator - Google Patents

Abstract

PURPOSE:To secure lubricating reliability in each compressor by making the operating frequency of a compressor being low in oil level height higher after operating each compressor with the same capacity just before stopping refrigerating cycle operation. CONSTITUTION:Before fully stopping refrigerating cycle operation, a command is issued to both first and second inverter units 3, 4 so as to make them operate each of compressors 1, 2 with the same operating frequency. During this interval, oil level height is detected by oil level sensors 13a, 13b, and after the elapse of the specified time, each operating frequency of these compressors 1, 2 according to a ratio of the oil level height. With this constitution, since each oil level height of these compressors 1, 2 is surely equalized, an amount of lubricating oil in these compressors 1, 2 is secured so that lubricating reliability is thus improvable.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention comprises a plurality of compressors connected in parallel to each other, and each compressor has an operating frequency controlled by an inverter device. The present invention relates to a refrigerating machine, and particularly relates to an improvement in an oil equalization control method for returning lubricating oil evenly to each compressor at the end of refrigeration cycle operation.

(Prior Art) For example, in showcases, so-called multi-type refrigerators that constitute a refrigeration cycle that controls a plurality of evaporators are often used. In this type of refrigerator, the range of refrigerating capacity for each evaporator is wide, and the requirements cannot be met with just one large compressor. That is, the capacity of the object to be frozen is often different for each evaporator, and there are also cases where only one evaporator is activated while the other evaporators are stopped. To meet these demands, rather than having one large compressor, multiple compressors are connected in parallel to operate a refrigeration cycle with a wide range of capacity according to the demands of each individual evaporator. methods have been adopted. Moreover, by connecting an inverter to each compressor and controlling its operating frequency separately, the refrigeration capacity can be varied, making it possible to achieve more precise refrigeration.

Incidentally, in such a compressor, lubricating oil is indispensable in order to always perform a smooth and reliable compression action. A portion of the lubricating oil collected in the compressor is discharged from the compressor in a state mixed with refrigerant gas, circulates through the refrigeration cycle circuit, and is sucked into the compressor again. Therefore, in a compressor equipped with a plurality of compressors whose operating frequency is controlled, lubricating oil is concentrated in a specific compressor, and the remaining compressors tend to run out of lubricating oil, and the refrigeration cycle operation often ends. If the refrigeration cycle is operated again in this state, the shortage of lubricating oil will become even greater, and it is considered that the compression efficiency will decrease due to the decrease in lubricity and the occurrence of mechanical damage accidents.

For this reason, it is necessary to take measures to equalize the amount of lubricating oil in each compressor. Conventionally, for example, there is a method in which the crankcase portions of each compressor are connected through a pipe to make the oil level uniform while the refrigeration cycle is stopped. However, since the amount of lubricating oil collected in each compressor constantly fluctuates depending on operating effects, it is difficult to set the diameter of the pipe. Furthermore, lubricating oil is conducted through the pipe even during operation of the refrigeration cycle, which increases the tendency for imbalance.

Alternatively, there is also a method of periodically operating all the compressors at full load to collect the accumulated lubricating oil in a predetermined container. However, in this case, there is a problem in that the oil amount fluctuates even more depending on the operating frequencies of the compressors that have been operating up to that point, and the difference in oil amount does not disappear.

(Problems to be Solved by the Invention) The present invention provides a refrigerator in which a plurality of compressors as described above are connected to each other in parallel and each is electrically connected to an inverter device. Refrigerator equalization eliminates the problem of uneven lubricating oil levels and ensures uniform oil level in each compressor when refrigeration cycle operation is stopped, ensuring lubrication reliability for each compressor. The purpose is to provide an oil control method.

[Structure of the invention]

(Means for Solving the Problem) That is, the present invention provides a method for stopping refrigeration cycle operation in a refrigerator in which a plurality of compressors are connected in parallel to each other and an inverter device is electrically connected to each compressor. Immediately beforehand, the inverter device sets each compressor to the same operating frequency, and the oil level detection mechanism senses the level of lubricating oil collected in each compressor, and then operates the compressor with a low oil level. This oil level control method for a refrigerating machine is characterized in that the frequency is set higher than the operating frequency of a compressor with a high oil level to make the oil level level of each compressor uniform.

(Function) The operating frequency of the compressor with a small amount of collected lubricating oil, that is, the oil level is raised, and lubricating oil is taken in from the compressor with a high oil level, so that the oil level detection mechanism always detects the difference between each compressor. The system detects the oil level and stops operation of each compressor when the oil level becomes equal.

(Example) Hereinafter, an example of the present invention will be described based on FIG. In the figure, 1 is a first compressor, 2 is a second compressor, and these are connected in parallel via a refrigerant pipe P on both the discharge side and the suction side.

Also, 1st. The second compressor 1.2 is electrically connected to the first inverter device 3 and the second inverter device 4, respectively, so that the operating frequencies thereof are mutually controlled. 1st. An oil return pipe 5 communicates with both the discharge side refrigerant pipe P and the suction side refrigerant pipe P of the second compressor 1゜2, and this oil return pipe 5 is provided with an electromagnetic on-off valve 6 and an oil separator 7. .

On the other hand, the first. The discharge-side refrigerant pipes P and the suction-side refrigerant pipes P of the second compressors 1 and 2 join together and communicate through one refrigerant pipe P. In the middle of this refrigerant pipe P, there is a condenser 8. Receiver 9.
Expansion valve 10. The evaporator 11 and the gas-liquid separator 12 communicate with each other in sequence, thus forming a refrigeration cycle. In addition, the above 1. The second compressors 1 and 2 are respectively provided with oil level sensors 13a and 13b, which are oil level detection mechanisms, and are electrically connected to a control circuit S. Above 1st and 2nd
Of course, the inverter device 3.4 is also electrically connected to the control circuit S. Further, a plurality of evaporators having the same capacity may be connected in parallel to the evaporator 11.

Therefore, depending on the refrigerating capacity required by the evaporator 11,
．． The second inverter devices 3 and 4 are connected to the first and second compressor 1.
．． The refrigeration cycle operation is performed by controlling the operating frequency of 2.

Refrigerant is the first. It is compressed by the second compressor 1.2 and guided to the discharge side refrigerant pipe P.

The oil separator 7 separates lubricating oil contained in this refrigerant, and the electromagnetic on-off valve 6 closes to collect the lubricating oil in the oil separator 7.

On the other hand, the refrigerant is sequentially conducted in the direction shown by the solid arrow, and each component performs the necessary refrigeration cycle action.

If such normal refrigeration cycle operation continues, the evaporator 11 will be in a state where refrigeration is not required.

At this time, each inverter device 3.4 lowers the operating frequency,
Alternatively, one compressor 1 or 2 is completely stopped.

Alternatively, by using the built-in timer or the timer function of an external timer, complete refrigeration cycle operation is always performed for a certain period of time. In any case, finally the first one. Second compressor 1
, 2 both reach a stopped state.

Then, before completely stopping the refrigeration cycle operation again, the control circuit S is activated by the first refrigeration cycle. A command signal is issued to the second inverter device 3-4 to operate each compressor 1, 2 at the same predetermined operating frequency for a predetermined period of time. Through this operation, if there is a difference in the amount of lubricating oil collected in each compressor 1.2, the difference can be identified. Oil level sensors 13a and 13b provided in each compressor 1 and 2 detect the oil level height, and send the detection signal to the control circuit S. This control circuit S
calculates the difference in oil level height and issues a command signal to each inverter device 3.4 again. That is, 1st. Depending on the ratio of the oil level height of the second compressor 1.2, the operating frequency of the compressor with a low oil level, for example 1, is controlled to be higher than the operating frequency of a compressor with a high oil level, such as 2. The amount of lubricating oil collected is small.

The compressor 1 with a low oil level can take in lubricating oil from the compressor 2 with a high oil level by increasing the operating frequency. At the same time, the electromagnetic on-off valve 6 is opened, and the lubricating oil collected in the oil separator 7 is actively collected into the first compressor 1. Each of the above oil level sensors 1
3a and 13b have reached the same oil level, the control circuit S switches the control circuit S to the first oil level. Second compressor 1.2
All operations will be stopped. That is, in a state where the refrigeration cycle operation is stopped, the first. The amount of oil collected in the second compressor 1.2 becomes uniform.

First mentioned above. The operation control state for the second compressors 1 and 2 can also be explained with reference to FIG. That is, 1st.
When a stop signal is issued from the normal operation of the second compressor 1.2, the same capacity operation is performed to determine the oil level, and then the oil level is checked. Then, it is operated at a predetermined operating frequency depending on the oil level height to equalize the oil level.

In addition, such a plurality of compressors 1 and 2 are connected in parallel,
Refrigerators each controlled by an inverter device 3.4 are advantageous in that the capacity can be varied over a wider range. However, especially when starting with an inverter, unbalanced starting tends to occur because the starting torque is small. For this purpose, control is performed such as starting them simultaneously and stopping them individually. However, with this kind of control, it is difficult to obtain a low refrigerating capacity immediately after the start of operation, and it is impossible if one compressor is operating while another compressor has to be operated due to load fluctuations. .

Therefore, a refrigeration cycle as shown in FIG. 3 is constructed.

That is, the first compressor 1 and the second compressor 2 are connected via the four-way valve 15. All remaining components are the same as those in the above embodiment, are given the same numbers, and description thereof will be omitted.

Under normal operating conditions, the four-way valve 15 is switched to communicate the discharge sides and suction sides of each compressor 1.2.

Therefore, each compressor 1.2 constitutes a parallel connection operation similar to the above embodiment, and the refrigerant is guided in the direction shown by the solid arrow in the figure.

On the other hand, at the time of starting the refrigeration cycle operation, or when only one compressor is in operation and other stopped compressors are started, control is performed as described below.

That is, for example, if the first compressor 1 is started first or is in operation, the four-way valve 15 is switched in the direction shown by the broken line arrow in the figure. The refrigerant discharged from the first compressor 1 is guided through the four-way valve 15 to the low pressure side of the second compressor 2, which is the suction side in normal operating conditions. and the second
In normal operating conditions, the refrigerant discharged from the discharge side, which is the high pressure side of the first compressor 2, passes through the four-way valve 15 to the first compressor 1.
is guided to the suction side of the In this state, if the second compressor 2, which has been stopped until now, is driven, this compressor 2
It can be started with almost no starting torque required. Then, when each compressor 1, 2 reaches a predetermined pressure, or a predetermined rotational speed, or after a predetermined period of time has elapsed, the four-way valve 15 is switched to supply the refrigerant again in the direction shown by the solid line arrow in the figure. It will guide you.

For refrigerators that can be controlled during startup, conventional refrigerators in which multiple (for example, two) compressors are connected in parallel and operated simultaneously are as shown in Figure 4 (A). This required the refrigeration capacity of two machines. On the other hand, according to the refrigerator using the new control method, the starting torque MIN is the same as that for one conventional refrigerator, as shown in Figure (B), which results in so-called energy saving and a variable range of capacity. can be fine-grained.

〔Effect of the invention〕

As explained above, according to the present invention, each compressor is operated at the same capacity immediately before stopping the refrigeration cycle operation, and then the operating frequency of the compressor with a low oil level is increased. It is possible to reliably equalize the oil level height, ensure the amount of lubricating oil in each compressor, maintain compression efficiency, and improve reliability.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a refrigeration cycle of a refrigerator showing an embodiment of the present invention, and FIG. 2 is a diagram specifically explaining its control method.
Fig. 3 is a refrigeration cycle configuration diagram of a refrigerator showing another embodiment of the present invention, Fig. 4 (A) is a characteristic diagram according to a conventional control method, and Fig. 4 (B) is a control method explained in Fig. 3. FIG. 3.4... (first and second) inverter device, 1°2
- (1st, 2nd) compressor, 13a, 13b--Oil level detection mechanism (oil level sensor). Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] In a refrigerator equipped with a plurality of compressors that are each electrically connected to an inverter device and communicated in parallel with each other, immediately before stopping the refrigeration cycle operation, each of the inverter devices causes each compressor to operate in the same predetermined manner. The oil level detection mechanism senses the level of lubricating oil collected in each compressor, and then adjusts the operating frequency of the compressor with low oil level to that of the compressor with high oil level. A refrigerating machine oil equalization control method characterized in that the oil level level of each compressor is made uniform at a higher frequency than the operating frequency and then the operation is stopped.