Motor cooling structure for turbo

A motor cooling structure for a turbo compressor is disclosed. The structure includes a refrigerant suction tube communicating with one lateral wall of the sealed container and extended from the evaporator, a first refrigerant flow tube communicating with another lateral wall of the sealed container, with the first refrigerant flow tube communicating with the first compression chamber, a second refrigerant flow tube through which the first compression chamber communicates with the second compression chamber, and a refrigerant discharge tube communicating with the second compression chamber communicating with a condenser, for thereby enhancing a cooling efficiency of the driving motor by directly introducing a low temperature refrigerant from an evaporator into a motor chamber.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to a turbo compressor compressing gas 
using a centrifugal force generated by an impeller, and in particular to a 
motor cooling structure for a turbo compressor which is capable of 
implementing an effective cooling operation of a driving motor by 
introducing a low temperature refrigerant gas from an evaporator into a 
motor chamber for thereby cooling the driving motor and changing a part of 
a liquid state refrigerant gas into a gas state based on the heat of the 
driving motor during the cooling operation for the driving motor for 
thereby removing an accumulator which is used for changing a liquid state 
refrigerant gas into a gas state refrigerant. 
2. Description of the Conventional Art 
Generally, the compressor is a machine for compressing a gas such as air, 
refrigerant gas, etc. based on a rotation operation of an impeller or a 
rotor or a reciprocating operation of a piston and is formed of a driving 
force generator for driving the impeller, rotor and piston and a 
compression mechanism for sucking gas based on the driving force generated 
by the driving force generator. 
The thusly constituted compressor is classified into a hermetically sealed 
type or a separation type based on the installed position of the driving 
force generator and the compression mechanism. In the hermetically sealed 
type compressor, the driving force generator and the compression mechanism 
are installed in a predetermined shaped sealed container, and in the 
separation type compressor, the driving force generator is installed 
outside the sealed container, so that the driving force generated by the 
driving force generator is transferred to the compression mechanism of the 
container. 
The hermetically sealed type compressor is classified into a rotary type 
compressor, a reciprocating type compressor a scroll type compressor. 
Recently, a turbo type compressor (or centrifugal type compressor) is 
disclosed, which is directed to sucking gas and compressing the same using 
a centrifugal force generated when the impeller is rotated. 
FIG. 1 illustrates the construction of a two-stage compression type turbo 
compressor having a Korean Patent Number 97-64567 invented by the inventor 
of this application. As shown therein, the conventional two stage turbo 
compressor includes a motor chamber 13 in which a driving motor 20 is 
installed at the inner center portion of a hermetically sealed container 
10 for generating a driving force. A first compression chamber 11 
communicating with an accumulator and a second compression chamber 12 is 
formed at both sides of the sealed container 10. 
In addition, a gas flow path 14 is formed along an inner circumferential 
surface of the hermetically sealed container 10 and an outer 
circumferential surface of the motor chamber 13 at an inner upper portion 
of the sealed container 10 for communicating the first and second 
compression chambers 11 and 12 with the motor chamber 13. An inlet hole 
13a is formed on a center lower surface of the gas flow path 14, namely, 
on the upper surface of the motor chamber 13, so that when the first 
compressed refrigerant gas flows from the first compression chamber 11 
into the second compression chamber 12 through the gas flow path 14, a 
part of the refrigerant gas flows into the interior of the motor chamber 
13 for thereby cooling the driving motor 20. An outlet hole 13b is formed 
so that the refrigerant gas which flowed into the motor chamber 13 through 
the inlet port 13a and cooled the driving motor 20 flows to the gas flow 
path 14 and then to the second compression chamber 12. 
In addition, the driving shaft 30 mounted at the motor chamber 13 is 
engaged with the driving motor 20 with its both ends being inserted into 
the first and second compression chambers 11 and 12, respectively. First 
and second impellers 40 and 50 are fixed at both ends of the driving shaft 
30 for sucking and compressing the refrigerant gas with its diameter in 
the direction that the gas is introduced being smaller than the diameter 
in the direction that the refrigerant gas is compressed and discharged, 
with its shape being conical when viewed from the driving shaft 30. 
In addition, the first and second compression chambers 11 and 12 include 
first and second inducers (not shown) communicating with the gas flow path 
14 for guiding the refrigerant gas sucked, and first and second diffusers 
11a and 12a and first and second volutes 11b and 12b for changing the 
kinetic energy of the refrigerant gas having its pressure increased by the 
first and second impellers 40 and 50 to a constant energy. 
A radial bearing 60 is engaged with the driving shaft 30 and the motor 
chamber 13 for thereby radially supporting the driving shaft 30 engaged 
with the driving motor 20 at both sides of the driving motor 20 engaged in 
the motor chamber 13. A thrust bearing 70 is fixedly engaged to the 
driving shaft 30 for supporting the driving shaft 30 at the outer portion 
of the radial bearing 60 and at the inner wall of both sides of the motor 
chamber 13. 
In the drawings, reference numeral 10a represents a suction port, and 10b 
represents a discharge port. 
The operation of the conventional 2-stage compression type turbo compressor 
will be explained with reference to the accompanying drawings. 
Namely, in the conventional two-stage compression type turbo compressor, 
when an induction magnetic field is formed at the driving motor 20 by the 
electric power applied, the driving shaft 30 is rotated at a high speed by 
the induction magnetic force. The first and second impellers 40 and 50 
fixed to both ends of the driving shaft 30 are rotated for thereby sucking 
the refrigerant gas from the evaporator (not shown) into the first 
compression chamber 11. 
At this time, since the refrigerant gas sucked from the evaporator into the 
first compression chamber 11 has a low temperature, a part of the 
refrigerant gas exists in a liquid state. When the compression process is 
executed, the compression efficiency is significantly decreased. 
Therefore, an accumulator is installed between the evaporator and the 
first compression chamber 11 for changing the liquid state refrigerant gas 
into a gas state and for transmitting the same into the first compression 
chamber. 
The refrigerant gas sucked into the first compression chamber 11 from the 
evaporator through the accumulator by the rotation force of the first and 
second impellers 40 and 50 is induced into the first inducer and then is 
accelerated by the first impeller 40. The thusly accelerated refrigerant 
gas is introduced into the first volute 11b through the first diffuser 11a 
and is first compressed thereby. 
The first compressed gas is sucked into the second compression chamber 12 
through the gas flow path 14 by the rotation force of the second impeller 
50. 
At this time, a part of the compressed gas sucked into the second 
compression chamber 12 through the gas flow path 14 flows into the 
interior of the motor chamber 13, in which the driving motor 20 is 
installed, through the inlet hole 13a formed on the lower surface of the 
gas flow path 14, namely, on the upper portion of the motor chamber 13, 
and the compressed gas cools the driving motor 20, and is discharged to 
the gas flow path 14 through the outlet hole 13b formed at the upper 
portion of the motor chamber 13 and then is combined with the first 
compressed gas and is sucked into the second compression chamber 12. 
The first compressed gas sucked into the second compression chamber 12 by 
the rotation force of the second impeller 50 is induced by the second 
inducer and accelerated by the second impeller 50, and the thusly 
accelerated refrigerant gas flows into the second volute 12b through the 
second diffuser 12a for thereby implementing a second stage compression. 
The thusly second compressed refrigerant gas is discharged into the 
condenser (not shown) through the discharge port 10b. 
In addition, since the driving shaft 30 is continuously rotated with no 
load during the refrigerant gas compression process, the driving shaft 30 
may move either in the radial direction or the axial direction. In order 
to overcome the abovedescribed problem, the movement of the same in the 
radial and axial directions is prevented by the radial bearing 60 disposed 
at both sides of the driving motor 20 and the thrust bearing 70 disposed 
at both outer portions of the radial bearing 60. 
In the conventional 2-stage compression type turbo compressor, the 
refrigerant gas is sucked from the evaporator into the compression 
chambers 11 and 12 by the centrifugal force of the impellers 40 and 50 
engaged with both ends of the driving shaft 30. At this time, the driving 
motor 20 is cooled using the first compressed gas. 
However, in the conventional 2-stage compression turbo compressor, the 
operation for cooling the driving motor is performed using a high 
temperature compressed gas which is first compressed by the first 
compression chamber, so that the cooling efficiency is decreased. 
In addition, in the conventional 2-stage compression turbo compressor, 
since the refrigerant gas introduced from the evaporator into the first 
compression chamber has a low temperature, a part of the refrigerant gas 
exists in a liquid state. If the refrigerant gas which partially exists in 
a liquid state is directly compressed, the compression efficiency is 
significantly decreased. Therefore, an accumulator is additionally needed 
for fully changing the liquid state refrigerant gas into a gas state and 
then introducing the same into the first compression chamber for 
increasing the compression efficiency, thereby increasing the fabrication 
cost. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a motor 
cooling structure for a turbo compressor which overcomes the 
aforementioned problems encountered in the conventional art. 
It is another object of the present invention to provide a motor cooling 
structure for a turbo compressor which is capable of enhancing a cooling 
efficiency of the driving motor by directly introducing a low temperature 
refrigerant from an evaporator into a motor chamber. 
It is another object of the present invention to provide a motor cooling 
structure for a turbo compressor which is capable of decreasing the 
fabrication cost by fully changing a part of the liquid state refrigerant 
gas introduced from the evaporator into the first compression chamber into 
a gas state refrigerant without using an accumulator. 
To achieve the above objects, there is provided a motor cooling structure 
for a turbo compressor which includes a refrigerant suction tube 
communicating with one lateral wall of the sealed container and extended 
from the evaporator; a first refrigerant flow tube communicating with 
another lateral wall of the sealed container, with the first refrigerant 
flow tube communicating with the first compression chamber; a second 
refrigerant flow tube through which the first compression chamber 
communicates with the second compression chamber; and a refrigerant 
discharge tube communicating with the second compression chamber 
communicating with a condenser. 
Additional advantages, objects and features of the invention will become 
more apparent from the description which follows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The motor cooling structure for a turbo compressor according to the present 
invention will be explained with reference to the accompanying drawings. 
As shown in FIG. 2, in a turbo compressor including a motor chamber in 
which a driving motor 120 is installed, a hermetically sealed container 
110 in which first and second compression chambers 111 and 112 communicate 
with each other for compressing a refrigerant gas sucked from both sides 
of the same, a driving shaft 130 engaged with the driving motor 120 with 
its both ends being inserted into the first and second compression 
chambers 111 and 112, and first and second impellers 140 and 150 engaged 
with both ends of the driving shaft 130 for compressing the refrigerant 
gas based on a two-stage centrifugal compression method. A motor cooling 
structure for the turbo compressor comprises a refrigerant suction tube 
113 communicating with one lateral wall of the sealed container 110 and 
extended from the evaporator (not shown); a first refrigerant flow tube 
114 communicating with another lateral wall of the sealed container 110, 
with the first refrigerant flow tube 114 communicating with the first 
compression chamber 111; a second refrigerant flow tube 115 through which 
the first compression chamber 111 communicates with the second compression 
chamber 112; and a refrigerant discharge tube 116 communicating with the 
second compression chamber 112 and communicating with a condenser (not 
shown). The refrigerant suction tube 113 and the first refrigerant flow 
tube 114 are connected with both sides of the driving motor 120. 
In addition, the refrigerant suction tube 113 and the first refrigerant 
flow tube 114 are connected with both sides of the driving motor 120 for 
implementing an easier flow of the refrigerant gas in the interior of the 
sealed container 110. 
In the drawings, reference numeral 160 represents a radial bearing, and 170 
represents a thrust bearing. 
The operation of the turbo compressor having a motor cooling structure 
according to the present invention will now be explained. 
Namely, in the turbo compressor having a motor cooling structure according 
to the present invention, when the driving shaft 130 is rotated by the 
driving motor 120, the first and second impellers 140 and 150 engaged with 
both ends of the driving shaft 130 are rotated to thereby suck a low 
temperature refrigerant gas from the evaporator through the refrigerant 
suction tube 113. 
The low temperature refrigerant gas sucked into the refrigerant suction 
tube 113 passes through the sealed container 110 and flows into the first 
refrigerant flow tube 114 since the refrigerant suction tube 113 
communicates with the sealed container 110. 
At this time, since the motor chamber is formed in the interior of the 
sealed container 110, the low temperature refrigerant gas sucked from the 
evaporator into the sealed container 110 through the refrigerant suction 
tube 113 passes through the interior of the sealed container 110 and cools 
the driving motor 120. 
In addition, a part of the refrigerant gas sucked from the evaporator into 
the sealed container 110 is in a liquid state. However, when the 
refrigerant gas containing a liquid state refrigerant passes through the 
interior of the sealed container 110 and cools the driving motor 120, the 
liquid state refrigerant is fully changed to a gas state by the heat 
generated by the driving motor 120, and the gas state refrigerant is 
discharged into the first refrigerant flow tube 114. 
The refrigerant gas discharged into the first refrigerant flow tube 114 is 
sucked into the first compression chamber 111 along the first refrigerant 
flow tube 114 and is accelerated by the first impeller 140 and is sprayed 
over the first diffuser 111a and the first volute 111b for thereby 
implementing a first compression operation. 
The thusly first compressed refrigerant gas is sucked into the second 
compression chamber 112 along the second refrigerant flow tube 115 
communicating with the first compression chamber 111 and is accelerated by 
the second impeller 150 and is sprayed over the second diffuser 112a and 
the second volute 112b for thereby implementing a second compression 
operation, and the second compressed refrigerant gas flows into the 
condenser through the refrigerant discharge tube 116 communicating with 
the condenser for thereby completing a compression process of the 
refrigerant gas. 
The connection between the sealed container 110 and the refrigerant suction 
tube 113 may be implemented based on a single tube connection. Preferably, 
the end portion of the refrigerant suction tube 113 extended from the 
evaporator or the accumulator may be divided into multiple connection 
portions for thereby connecting the refrigerant suction tube 113 to both 
sides of the driving motor 120 of the sealed container 110. The first 
refrigerant flow tube 114 may be connected to both sides of the driving 
motor 120 like the refrigerant suction tube 113 for thereby implementing 
an efficient refrigerant flow in the sealed container 110 for thereby 
enhancing the efficiency of the compressor. 
The present invention may be well applicable for a face-to-face structure 
in which the suction portions of the first and second impellers 140 and 
150 are opposite to each other. 
As described above, in the motor cooling structure for a turbo compressor 
according to the present invention, since a low temperature refrigerant 
gas from the evaporator sucked by the rotation of the first and second 
impellers passes through the interior of the sealed container and flows 
into the first compression chamber, so that the low temperature 
refrigerant gas directly cools the driving motor for thereby enhancing the 
cooing efficiency of the driving motor. 
In particular, a liquid state refrigerant which flows from the evaporator 
passes through the interior of the sealed container and is fully changed 
to a gas state refrigerant during the process for cooling the driving 
motor. Therefore, in the present invention, an accumulator is not needed 
for fully changing the liquid state refrigerant into a gas state 
refrigerant for thereby increasing the fabrication cost and implementing a 
simple structure of the turbo compressor. 
Although the preferred embodiments of the present invention have been 
disclosed for illustrative purposes, those skilled in the art will 
appreciate that various modifications, additions and substitutions are 
possible, without departing from the scope and spirit of the invention as 
recited in the accompanying claims.