FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
A BALANCED OIL RECOVERY AND CONTROL SYSTEM FOR A MULTI-AIR-CONDITIONER SYSTEM AND A METHOD THEREOF;
BLUE STAR LIMITED A COMPANY
INCORPORATED UNDER THE
COMPANIES ACT, 1956, WHOSE ADDRESS IS KASTURI BUILDINGS, MOHAN T. ADVANI CHOWK, JAMSHETJI TATA ROAD, MUMBAI - 400 020, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION
The present invention relates to multi-air-conditioners, and more particularly, to a balanced oil recovery and control system for a multi-air-conditioner system and a method thereof.
DISCUSSION OF THE RELATED ART
Generally, the air conditioner cools and/or heats rooms as the air conditioner performs steps of compression, condensing, expansion, and evaporation of refrigerant. In air conditioning systems, there are cooling air conditioner for supplying cold air to the room by operating a refrigerating cycle only in one direction, and cooling/heating air conditioner for supplying cold or warm air to the room by operating the refrigerating cycle in either direction, selectively.
Moreover, there are general air conditioners in which one indoor unit is connected to one outdoor unit, and multi-air-conditioner in which a plurality of indoor units are connected to one or more outdoor unit.
In the refrigeration process, compressor sucks vapor of refrigerant, compresses and discharge the compressed refrigerant to condenser. As the compressor is filled with lubrication oii, a part of the lubrication oil also flows into the refrigerating cycle together with the refrigerant as the compressor discharges the compressed refrigerant and returns to the compressor. As today's refrigerant system has a larger spread, the refrigerant pipes traverse long lengths. Long refrigerant piping loops raise concerns about oii return. Consequently, it sometime happens that the supply of the lubrication oil becomes insufficient in the compressor. When the supply of the lubrication oil becomes insufficient, a sliding portion comes to run out of • the oii, which exerts an unfavorable influence upon the life of the compressor. To avoid this, generally, an oil separator is provided per outdoor unit. Periodically, the refrigeration system goes into oil retrieval mode/oil recovery operation during which

time the thermostatic/electronic expansion valve opens, and the compressor cycles at high pressure to flush oil out of any location where it has accumulated.
US 7,467,521 discloses a method for controlling multi-type air conditioner in which operation time periods of an outdoor unit is integrated, to determined a time point when an oil recovery operation is performed, and performing the oil recovery operation only when a summed rates, or a number of indoor units accessed with communication is higher than a value preset at a control means.
However, the above discussed prior arts conduct only oil recovery and are limited to only single outdoor unit. Moreover, US 7,467,521 conducts oil recovery only when the predetermined number of indoor units are 'ON'. Further, presently in a multi-air-conditioner system having plurality of outdoor units, the outdoor units are connected to each other to circulate the oil with a common pipeline. However, this leads into recovery of oil less for some outdoor units and high for other outdoor units resulting in increase risk of failure of the compressors and stoppage of the multi-air-conditioner systems due to failure of compressor.
Therefore, there is a need of providing a system and method for a balanced oil recovery and control system for a multi-air-conditioner system comprising more than one outdoor units.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a balanced oil recovery and control system for a multi-air-conditioner system and a method thereof that substantially obviates one or more problems due to limitations and disadvantages of the related art.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention

may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, is a balanced oil recovery and control system for a multi-air-conditioner system having a plurality of indoor units each having an evaporator means, a plurality of outdoor unit having atleast one compressor and a condenser means, an oil separator for each outdoor unit and a plurality of expansion valves provided, respectively, for said plurality of indoor units for controlling the flow of refrigerant circulating through one or more said outdoor units and said plurality of indoor units. The said balanced oil recovery and control system comprises a first control means for periodically initiating flush cycles by starting all outdoor units and opening all expansion valves for full flow therethrough during the flush cycle so that compressor lubricant is oils flushed which may have accumulated pipelines and indoor units, a first control means for periodically initiating flush cycles by starting all outdoor units and opening all expansion valves for full flow therethrough during the flush cycle so that said evaporator means is flushed of compressor lubricant oils which may have accumulated therein, a first connecting means with a first valve for connecting a first outlet of the oil separator to an inlet of the compressor within the outdoor unit, a second connecting means for connecting a second outlet of oil separator of the compressor of one outdoor unit to the inlet of the compressor of the next outdoor unit with a second valve; and a second control means to open said second valve on second connecting means and to close the first valve for swapping oil from the oil separator of the compressor of one outdoor unit to the compressor of one of the next outdoor unit along with the flushing cycle in order to balance the oil in the compressors.
The present invention also provides a method for controlling recovery and oil balancing for a multi-air-conditioner system having a plurality of indoor units, each having an evaporator means, a plurality of outdoor unit having atleast one compressor and a condenser means, an oil separator for each outdoor unit and a plurality of expansion valves provided, respectively, for said plurality of indoor units

for controlling the flow of refrigerant circulating through said compressor and said plurality of indoor units, said method comprising steps of: carrying flushing cycle to flush of compressor lubricant oils which may have accumulated therein; and swapping oil from the oil separator of the compressor of one outdoor unit to the compressor of one of the next outdoor unit simultaneously in order to balance the oil in the compressors.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:
FIG. 1 illustrates a block diagram of a multi-air-conditioner system in accordance with a preferred embodiment of the present invention;
FIG. 2 illustrates a flow chart showing the steps of a method for controlling recovery and oil balancing the multi-air-conditioner in FIG. 1 in accordance with a first preferred embodiment of the present invention;
Figure 3 illustrates connection between the oil separators and compressors of three ODU according to the preferred embodiment of the present invention; and
Figure 4 illustrates swapping of oil from the oil separator of one ODU to compressor of the next ODU through Figure 4A to Figure 4B.
DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

In general, the present invention provides a balanced oil recovery and control system for a multi-air-conditioner system having a plurality of Indoor Units (IDU) each having an evaporator means, a plurality of Outdoor Units (ODU) having atleast one compressor and a condenser means, an oil separator for each outdoor unit and a plurality of expansion valves provided, respectively, for said plurality of indoor units for controlling the flow of refrigerant circulating through one or more said outdoor units and said plurality of indoor units wherein the balanced oil recovery and control system swaps oil from oil separator of one ODU to a compressor of next ODU in order to balance the oil in the compressors.
The present invention is explained with a multi-air-conditioner system having three ODUs in detailed herein below with the reference figures 1-4.
Referring to FIG. 1, the multi-air-conditioner system includes a plurality of indoor units connected to a plurality of ODUs. The outdoor unit may include two or more outdoor units/set depending on capacity of a system. In FIG. 1, the multi-air-conditioner system (100) comprises three number of ODUs, each comprising one compressor (C) and an oil separator (OS). The ODU may comprise more than one compressor with a known oil balancing system within the ODU and connected to the oil separator. If the outdoor unit includes more than one compressors, one of the compressors may be a variable capacity compressor of which capacity can be varied.
The balanced oil recovery and control system according to the present invention as shown in Figure 1 includes two control means (112, 114). The first control means (112) is for controlling the outdoor sets (120) and the indoor units (140) for carrying out flushing cycle periodically and the second control means (114) for swapping the oils according to the present invention. The first control means (112) is connected to ODUs (120), the IDUs (140), and with communication lines of the IDUs and ODUs. The second control means is connected to the oil separators (OS) and compressors (C) for swapping oil. The connection between the oil separators and the compressors according to the present invention is shown in Figure 3.

Referring to Figure 3, according to the present invention, each ODU (ODU1, ODU2, ODU3) comprises one oil separator (OS1, OS2, OS3). Each oil separator (OS1, OS2, OS3) has two outlets for transferring oil. One of the outlets of the oil separators (OS1, OS2, OS3) is connected to the compressor or inner oil balancing line (not shown) of the inlet of compressors of the ODU to which the oil separator is connected via a first solenoid valve (SV1) with the help of first pipeline and other outlet of the oil separator of an ODU is connected to inlet of compressor of next ODU via second solenoid valve (SV2) and third solenoid valve (SV3) with the help of second pipeline. As shown in Figure 3, a common oil copper pipe line is used to connect the second outlet of oil separators to compressors with solenoid valves. Alternatively, a separate oil copper pipe line can be used to connect the second outlet of the oil separator of one ODU to the compressor of next or other ODU with one solenoid valve and the oil separator of the last ODU is connected to the compressor of the first ODU.
A method for controlling recovery and oil balancing for the multi-air-conditioner system in accordance with preferred embodiment of the present invention will be described with reference to Figures 2 and 4 through 4A to 4C.
Upon putting the outdoor unit into operation, the first control means integrates operation time periods of the outdoor unit. It is preferable that the operation time periods of the compressor are integrated. This is for starting an oil recovery operation with reference to the operation time period of the compressor because the longer the operation time period of the compressor, the greater the amount of oil accumulated in the indoor unit.
During normal operation, the second control means keeps open the first solenoid valve(SVI) of the ODU of which compressor is running for returning the oil separated in the oil separated during normal operation to the compressor of that ODU.

The first controller (112) determines whether the integrated time period of the compressor reaches to a predetermined time period preset. If it is determined that the integrated time period of the compressor reaches to a predetermined time period preset at the first control means, the first control means starts oil recovery operation. Generally recovery operation/Hushing cycle is carried out for three minutes. According to the present invention, the recovery operation/flushing cycle is carried out preferably after every 4 hours. In other word, the integrated preset time period is about 4 hours.
Once the oil recovery operation is started, the first control means opens all expansion valves provided, respectively, for said plurality of indoor units for controlling the flow of refrigerant circulating through said compressor and said plurality of indoor units and start all the ODUs and operates all the compressors at a increased capacity. The first control means initially operates the system at low capacity and gradually increases to a required or predefined capacity. In the present invention, during oil recovery, the system is preferably operated to 50% of total capacity for 1 minute and then 75% of total capacity. This is done to minimize a pressure shock waves in said refrigerant system on opening of said expansion valve. In this instance, since refrigerant flow speed and rate of the system increase significantly, refrigerant accumulated in the all the IDUs is recovered to the compressors along with the oil in the oil separators. Simultaneously, the second control means (114) based on the response of the first controller, closes the first solenoid valve (SV1) provided over the outlet of all the oil separator and opens the solenoid valve(s) over the second pipeline for swapping oil from oil separator of one ODU to the compressor of the other ODU for balancing the oil between two or thee connected ODUs. The swapping of the oil according to the present invention is explained herein below with the reference of Figures 4A-4C
As shown in the Figures 4A, the second control means opens the second solenoid valve (SV2) of ODU1 that makes the ODU1 as supplier and third solenoid valve (SV3) of ODU2 to transfer oil accumulated in the oil separator (OS1) of ODU1 to the compressor (C2) of the ODU2 which becomes a receiver. On completion of oil transfer or after a predetermined time, the second control means closes the second

solenoid valve (SV2) of ODU1 and third solenoid valve (SV3) of ODU2 and simultaneously opens the second solenoid valve (SV2) of ODU2 that makes the ODU2 as supplier and third solenoid valve (SV3) of ODU3. The oil accumulated in the oil separator (OS2) of ODU2 is then transferred to the compressor (C3) of the ODU3 making ODU3 as a receiver. Similarly, on completion of oil transfer or after a predetermined time, the second control means closes the second solenoid valve (SV2) of ODU2 and third solenoid valve (SV3) of ODU3 and simultaneously opens the second solenoid valve (SV2) of ODU3 that makes the ODU3 as supplier and third solenoid valve (SV3) of ODU1 to transfer oil accumulated in the oil separator (OS3) of ODU3 to the compressor (C1) of the ODU1 which becomes a receiver. In this case, the time for transferring the oil may be equally divided by dividing the total oil recovery time by the number of the ODUs. For example the total oil recovery time is 3 minute and there are 3 ODUs, then the oil transfer/swapping time for each ODU will be 1min. Alternatively, if the each oil separator of one ODU is connected to compressor of the second ODU with separate pipeline, then the second solenoid valve provided over the said separate line remains open for total period of the oil recovery operation.
The system and the method of the present invention allows maximum recovery of the oil, oil balancing in the compressor by supplying oil from a compressor having excess oil to the compressor having less oil. Further oil recovery and balancing of the oil takes simultaneously. The system is simple and easy. Moreover, the present invention recovers oil from all indoor units irrespective of their ON/OFF status.
It will be apparent to those skilled in the art that various modifications and variations such as providing one outlet for oil separator with two branch outlets or using three way valves etc. can be made in the present invention without departing from the spirit or scope of the inventions i.e. swapping oil from one ODU to other ODU during the oil recovery process. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

We Claim:
1. A balanced oil recovery and control system for a multi-air-conditioner system
having a plurality of indoor units each having an evaporator means, a plurality of
outdoor unit having atleast one compressor and a condenser means, an oil
separator for each outdoor unit and a plurality of expansion valves provided,
respectively, for said plurality of indoor units for controlling the flow of refrigerant
circulating through one or more said outdoor units and said plurality of indoor
units, said balanced oil recovery and control system comprising:
a first control means for periodically initiating flush cycles by starting all outdoor
units and opening all expansion valves for full flow therethrough during the flush
cycle so that said evaporator means is flushed of compressor lubricant oils which
may have accumulated therein;
a first connecting means with a first valve for connecting a first outlet of the oil
separator to an inlet of the compressor within the outdoor unit;
a second connecting means for connecting a second outlet of oil separator of the
compressor of one outdoor unit to the inlet of the compressor of the next outdoor
unit with a second valve;
and
a second control means to open said second valve on second connecting means
and to close the first valve for swapping oil from the oil separator of the
compressor of one outdoor unit to the compressor of one of the next outdoor unit
along with the flushing cycle in order to balance the oil in the compressors.
2. The system as claimed in claim 1 wherein the first control means increases capacity of the system gradually during flushing cycle to minimize a pressure shock waves in said refrigerant on opening of said expansion valve.
3. The system as claimed in claim 1, wherein the first control means initiates flushing cycle at about after every 4 hours.
4. The system as claimed in claim 1, wherein the first valve and the second valve can be solenoid actuated valves.

5. The system as claimed in claim 1, wherein second connecting means can be a common connecting means for connecting oil separators of one outdoor unit with the compressor of the next outdoor unit.
6. The system as claimed in claim 1, wherein second connecting means can be a separate connecting means for connecting oil separator of one outdoor unit to compressor of the other outdoor unit.
7. A method for controlling recovery and oil balancing for a multi-air-conditioner system having a plurality of indoor units, each having an evaporator means, a plurality of outdoor unit having atleast one compressor and a condenser means, an oil separator for each outdoor unit and a plurality of expansion valves provided, respectively, for said plurality of indoor units for controlling the flow of refrigerant circulating through said compressor and said plurality of indoor units, said method comprising steps of:
carrying flushing cycle to flush of compressor lubricant oils which may have accumulated therein; and
swapping oil from the oil separator of the compressor of one outdoor unit to the compressor of one of the next outdoor unit simultaneously in order to balance the oil in the compressors.
8. The method as claimed in claim 7, wherein carrying flushing cycle includes
starting all outdoor units and opening all expansion valves over the indoor units
for full flow of refrigerant after a predetermined period.

9. The method as claimed in claim 7, wherein the method comprises a step of increasing capacity of the system gradually during flushing cycle to minimize a pressure shock waves in said refrigerant on opening of said expansion valve.