U.S. patent application number 11/836189 was filed with the patent office on 2008-02-14 for screw compressor.
Invention is credited to Yasuaki Iizuka, Kenji Tojo, Ryuichiro Yonemoto.
Application Number | 20080038127 11/836189 |
Document ID | / |
Family ID | 39050984 |
Filed Date | 2008-02-14 |
United States Patent
Application |
20080038127 |
Kind Code |
A1 |
Yonemoto; Ryuichiro ; et
al. |
February 14, 2008 |
SCREW COMPRESSOR
Abstract
A screw compressor is for use of a screw chiller, and comprises
a pair of screw rotors and a casing housing the screw rotors, a
capacity control valve for varying a ratio of volume, a motor for
driving the screw rotors and an inverter for varying the rotational
speed of the motor. The screw compressor is controlled using
rotational speed control means by the inverter and mechanical
capacity control means by the capacity control valve independently
or combined together according to loads. The maximum efficient
point in a capacity control performed solely by the inverter is set
to a rotational speed side lower than the rated operation point. In
a region where the rotational speed is higher than the maximum
efficient point, the inverter solely takes control from a rated
rotational speed to a high rotational speed side.
Inventors: |
Yonemoto; Ryuichiro;
(Shizuoka, JP) ; Iizuka; Yasuaki; (Shizuoka,
JP) ; Tojo; Kenji; (Moriya, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
39050984 |
Appl. No.: |
11/836189 |
Filed: |
August 9, 2007 |
Current U.S.
Class: |
417/423.8 ;
418/206.3 |
Current CPC
Class: |
F04C 2270/42 20130101;
F04C 28/125 20130101; F04C 2240/52 20130101; F04C 2270/44 20130101;
F04C 2270/70 20130101; F04C 2270/18 20130101; F04C 18/16 20130101;
F04C 28/08 20130101; F04C 2270/19 20130101; F04C 2240/403
20130101 |
Class at
Publication: |
417/423.8 ;
418/206.3 |
International
Class: |
F04B 17/00 20060101
F04B017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2006 |
JP |
2006-218438 |
Claims
1. A screw compressor for a screw chiller, comprising: a pair of
screw rotors; a casing housing the screw rotors; a capacity control
valve for varying a ratio of volume; a motor for driving the screw
rotors; and an inverter for varying a rotational speed of the
motor, wherein the screw compressor is controlled using rotational
speed control means by the inverter and mechanical capacity control
means by the capacity control valve either independently or
combined together according to loads, and wherein the maximum
efficient point in the capacity control performed solely by the
inverter is set to a rotational speed side lower than a rated
operation point, and in a region where the rotational speed is
higher than the maximum efficient point, the inverter solely takes
control from a rated rotational speed to a high rotational speed
side.
2. The screw compressor according to claim 1, wherein when an
operation at a rotational speed region at or below the maximum
efficient point is demanded, the rotational speed control means by
the inverter and the mechanical capacity control means by the
capacity control valve are used concurrently according to
capacities so that efficiency becomes the maximum.
3. The screw compressor according to claim 1, wherein the capacity
control valve varies a compression starting position provided in
the casing.
4. The screw compressor according to claim 1, wherein the maximum
efficient point is set to around 80% of a rated refrigerating
capacity when an independent capacity control by the inverter is
performed.
5. The screw compressor according to claim 2, wherein a position of
the capacity control valve is controlled based on the rotational
speed of the motor according to a suction pressure, a discharge
pressure and a load of the pair of the screw rotors.
6. The screw compressor according to claim 1, wherein when an
anomaly occurs on the inverter and a continuous operation of the
motor by the inverter is made impossible, the motor is directly
connected to a commercial power in an emergency manner and the
capacity controlled operation by the capacity control valve is
continued same as before.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a screw compressor, and in
particular, relates to a screw compressor suitable for a screw
chiller.
[0002] As a screw compressor used for a conventional refrigerating
apparatus, there is the one disclosed in JP-A-59-211790. A scroll
wrap compressor of JP-A-59-211790 operates to vary a ratio of
volume by performing an unload control with a capacity control
valve (slide valve) in the capacity control range of 100% to 75% of
a refrigerating capacity. Further, in the capacity control range of
75% to 37.5% of the refrigerating capacity, the scroll wrap
compressor increases the rotational speed of the screw compressor
by 1.5 times by an inverter, and by using the capacity control
valve in the range of 50% to 25% of the refrigerating capacity, can
operate to vary the ratio of volume. Such operation can provide
efficiency better than when operated under a 100% load.
[0003] Further, as another conventional screw compressor, there is
the one disclosed in JP-A-2004-137934. The screw compressor of
JP-A-2004-137934 concurrently uses a rotating speed control by
means of an inverter and a compression ratio control for varying
the ratio of volume by changing the end of the compression stroke
by means of a variable VI valve at the time of adjusting the
capacity so that the optimum compressor efficiency is attained
depending on the operating condition of the screw compressor.
[0004] Because the screw compressor in JP-A-59-211790 adopts an
operating method in which the rotational speed is increased to a
constant rotational speed and a capacity control valve is used in
the range of 50% to 25%, there is a problem that a highly improved
performance cannot be expected because of the increase in
mechanical loss due to the increased speed and a bypass imposed by
the capacity control valve.
[0005] In the screw compressors in JP-A-59-211790 and
JP-A-2004-137934, no disclosure has been made regarding the
effective use of the screw compressors as one for a screw chiller.
That is, a compressor for the screw chiller is often operated at a
refrigerating capacity ratio lower than the 100% rated
refrigerating capacity ratio, that is, in the vicinity of 80% of
the rated ratio, whereas, the screw compressors in JP-A-59-211790
and JP-A-2004-137934 are controlled such that the maximum efficient
point is attained at rated operation, and therefore, effective
operation has not been provided as the compressor for the screw
chiller.
[0006] An object of the present invention is to obtain a screw
compressor capable of operation performing an effective operation
for a screw chiller.
SUMMARY OF THE INVENTION
[0007] To achieve the above described object, a screw compressor
for a screw chiller according to the present invention comprises a
pair of screw rotors, a casing housing the screw rotors, a capacity
control valve for varying a ratio of volume, a motor for driving
the screw rotors, and an inverter for varying rotational speed of
the motor, wherein the screw compressor is controlled using
rotational speed control means by the inverter and mechanical
capacity control means by the capacity control valve either
independently or combined together according to a load, and wherein
the maximum efficient point in a capacity control performed solely
by the inverter is set to a rotational speed side lower than rated
operation point, and in an area where the rotational speed is
higher than the maximum efficient point, the inverter solely takes
control from a rated rotational speed to a high rotational speed
side.
[0008] Specific preferable configuration examples according to the
present invention are as follows.
[0009] (1) When an operation in the rotational speed range at or
below the maximum efficient point is demanded, the rotational speed
control means by the inverter and the mechanical capacity control
means by the capacity control valve are used concurrently according
to the capacities, thereby operating such that an efficiency
becomes the maximum.
[0010] (2) The capacity control valve varies a compression starting
position provided in the casing.
[0011] (3) The maximum efficient point is set around 80% of the
rated refrigerating capacity when the capacity control is performed
independently by the inverter.
[0012] (4) The position of the capacity control valve is controlled
based on the rotational speed of the motor according to a suction
pressure, a discharge pressure, and the load of the pair of screw
rotors.
[0013] (5) When an anomaly occurs on the inverter, so that the
continuous operation of the motor by the inverter is made
impossible, the motor is directly connected to a commercial power
in an emergency manner, thereby the capacity controlled operation
is continued by the capacity control valve same as before.
[0014] According to the present invention, a screw compressor
capable of performing an effective operation as a screw chiller can
be obtained.
[0015] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a sectional view of a screw compressor showing one
embodiment of the present invention;
[0017] FIG. 2 is an operation explanatory view of a capacity
control valve in FIG. 1; and
[0018] FIG. 3 is a view showing a characteristic curve of
compressor efficiency relative to refrigerating capacity ratio in
the screw compressor of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Hereinafter, one embodiment of the present invention will be
described with reference to FIGS. 1 to 3. FIG. 1 is a sectional
view of a screw compressor showing an embodiment of the present
invention, FIG. 2 is an operation explanatory view of a capacity
control valve in FIG. 1, and FIG. 3 is a view showing a
characteristic curve of compressor efficiency relative to
refrigerating capacity ratio in the screw compressor of FIG. 1.
[0020] A screw compressor 50 is constituted by a screw compressor
for a screw chiller comprising a compressor portion 17, a motor
portion 18 and a control device 23. Refrigerant gas to be
compressed flows to the compressor portion 17 through the motor
portion 18, and after being compressed by the compressor portion
17, is discharged outside the compressor. While the screw
compressor 50 performing a capacity control operates in such a
manner that the rotational speed and the position of a capacity
control valve are changed so that pressure becomes constant, the
control pressure is set to an arbitrary pressure.
[0021] The compressor portion 17 comprises a main casing 1, screw
rotors 2, a capacity control valve 11, a rod 12, a hydraulic piston
13, a coil spring 14, a discharge casing 21, roller bearings 6 and
7, a ball bearing 8, and the like.
[0022] The main casing 1 forms a suction port 9, a discharge port
10, a gas outlet 19, and the like. The suction port 9 forms a
suction flow passage toward the screw rotors 2, and the discharge
port 10 forms a discharge passage from the screw rotors 2, and the
gas outlet 19 forms a discharge flow passage toward the outside.
The discharge casing 21 is disposed opposite to the motor of the
main casing 1, and is fixed to the main casing 1.
[0023] The screw rotors 2 are constituted by a pair of a male rotor
2A and a female rotor (not shown) which are engaged with each
other, and is housed in a pair of cylindrical bores (not shown).
Shaft portion provided at both sides of the male rotor 2A are
respectively supported by the roller bearing 6 disposed in the main
casing 1 and the roller bearing 7 and the ball bearing 8 disposed
in the discharge casing 21.
[0024] The capacity control valve 11 is for performing a capacity
control by bypassing a part of refrigerant gas sucked into the
engaged portion of the screw rotors 2 toward the suction side, and
is movably housed in a concave portion 1b extending laterally.
According to motor frequency controlled by the inverter 5, a
position of the capacity control valve 11 attaining the best
efficiency is controlled. The capacity control to bypass a part of
the sucked refrigerant gas to the suction side can be efficiently
performed as compared with capacity control to bypass a part of
discharge gas to the discharge side. The hydraulic piston 13 is a
piston for driving the capacity control valve 11 left and right
through the rod 12, and is slidably housed in a cylinder 15 which
extends laterally. The coil spring 14 is disposed at a capacity
control valve chamber side of the cylinder 15, and always applies a
force to press the hydraulic piston 13 toward a side opposite to
the capacity control valve. A capacity control mechanism
(mechanical capacity control means) is constituted by the capacity
control valve 11, the rod 12, the hydraulic piston 13, and the coil
spring 14.
[0025] The motor portion 18 comprises a motor casing 16, a driving
motor 22 and the like, and is disposed such that driving force of
the motor portion 18 is transmitted to the compressor portion 17.
The motor casing 16 and the main casing 1 are fixed to each other
with both end surfaces thereof in closely contact with each other,
and at the same time, the interiors thereof are communicated with
each other. A side surface opposite to the compressor side of the
motor casing 16 is formed with a gas inlet 20 for sucking the
refrigerant gas to be compressed.
[0026] The driving motor 22 is constituted by a motor stator 3 and
a motor rotor 4, and is disposed inside the motor casing 16. The
motor stator 3 is arranged on the inner peripheral surface of the
motor casing 16. The motor rotor 4 is fixed to the shaft portion
formed at one side of the male rotor 2A, and is rotatably disposed
inside the motor stator 3. By such structure, the driving force of
the driving motor 22 is transmitted to the male rotor 2A. Note that
the female rotor is driven by the male rotor 2A.
[0027] The control device 23 comprises an inverter 5 for
controlling a rotational speed of the driving motor 22, and a valve
control portion 26 for controlling the position of the capacity
control valve 11.
[0028] The inverter 5 controls the rotational frequency of the
motor portion 22 according to loads. The control device 23 is
connected with a power supply, a suction pressure sensor 24, and a
discharge pressure sensor 25. The suction pressure sensor 24 is a
sensor for detecting a suction pressure of the compressor, for
example, a pressure of the gas inlet 20 to input to the control
device 23. The discharge pressure sensor 25 is for detecting the
discharge pressure of the compressor, for example, a pressure of
the gas outlet 20 to input to the control device 23.
[0029] The screw compressor 50 is constituted to be controlled
using rotational speed control means by the inverter 5 and
mechanical capacity control means by the capacity control valve 11
either independently or combined together according to loads.
Further, the screw compressor 50 is structured such that the
maximum efficient point when an independent capacity control is
performed by the inverter 5 is set in a rotational speed side lower
than the rated operation point and the region in which the
rotational speed is higher than the maximum efficient point is
controlled by the inverter alone from the rated rotational speed to
the high rotational speed side. Further, the screw compressor 50 is
structured such that, when the operation in a rotational speed
range at or below the best efficiency point is required, both of
the rotational speed control means by the inverter 5 and the
mechanical capacity control means by the capacity control valve 11
are used according to the capacities so as to perform the operation
in which the efficiency becomes the maximum.
[0030] The valve control portion 26, even when an anomaly occurs on
the inverter 5 and the continuous operation by the inverter 5 is
made impossible, directly connects the motor 22 to a commercial
power in an emergency manner so as to effect a capacity control by
the capacity control valve 11, and performs a control such that a
capacity controlled operation by the capacity control valve 11 is
continued same as before. In this manner, the operational
reliability of the screw compressor 50 can be improved.
[0031] In the screw compressor 50 thus structured, by supplying the
power to the driving motor 22 through the inverter 5, the driving
motor 22 is rotated by the predetermined rotational speed by the
inverter 5, and further, the compressor portion 17 is rotated. As a
result, the refrigerant gas to be compressed is sucked into the
motor casing 16 through the gas inlet 20, and cools the driving
motor 22, and thereafter is sucked into the screw rotors 2 through
the suction port 9, and after being compressed by the screw rotor
2, is discharged to the discharge flow passage from the discharge
port 10, and further, is discharged to an outside flow passage from
the gas outlet 19.
[0032] The refrigerating cycle of the screw chiller, as shown in
FIG. 1, is structured by connecting the screw compressor 50, a
condenser 27, an expansion valve 28, and an evaporator 29 in order
in annular manner. High temperature and high pressure refrigerant
discharged from the screw compressor 50 is condensed by the
condenser 27 by heat exchange with the air by a fan 30 so as to
become a low temperature and high pressure liquid refrigerant to be
supplied to the expansion valve 28. The low temperature and low
pressure liquid refrigerant depressurized by the expansion valve 28
is evaporated by heat exchange with water of a cold water piping
29b by a refrigerant piping 29a of the evaporator 29 so as to
become a low pressure gas to be returned to the screw compressor
50. The cold water cooled by the cold water piping 29b is used for
cooling control.
[0033] A temperature sensor 31 is attached to the cold water piping
29b of the evaporator 29, and a detection signal representing a
cooling water temperature from the temperature sensor 31 is input
to the control device 23. So, the control device 23, taking the
cooling water temperature based on the input detection signal as
information from a load side, controls the inverter 5 and the
capacity control valve 11 to perform capacity adjustment for the
load.
[0034] In the screw compressor 50, capacity adjustment for the load
is executed by inputting the signal from the suction pressure
sensor 24 and the signal from the discharge pressure sensor 25 into
the control device 23, and at the same time, by inputting the
signal from the temperature sensor 31 to the control device 23, and
based on these signals, by performing the rotational speed control
of the driving motor 22 by the inverter 5 and the position control
of the capacity control valve 11 by the valve control portion
26.
[0035] The capacity adjustment for the load, as described above, is
performed by the control of the inverter 5 alone from the rated
rotational speed to the high rotational speed side in the region
where the rotational speed is higher than the maximum efficient
point when the independent capacity control is performed by the
inverter 5, and by a combination of the rotational speed control by
the inverter 5 and the mechanical capacity control by the capacity
control valve 11 so that the efficiency becomes the maximum
according to the capacity in the region where the rotational speed
is at or below the maximum efficient point.
[0036] Here, in the region where the refrigerating capacity ratio
is higher than the refrigerating capacity ratio serving as the
maximum efficient point (refrigerating capacity ratio of 80% of the
rating in the present embodiment), as shown in FIG. 2(a), the
capacity control valve 11 is moved to the motor side in the shaft
direction so as not to bypass the refrigerant gas, and the
rotational speed of the driving motor 22 is controlled by the
inverter 5. Further, in the region where the rotational speed is at
or below the maximum efficient point, as shown in FIG. 2(b), the
capacity control valve 11 is moved opposite to the motor side in
the shaft direction so as to bypass the refrigerant gas to the
suction side, and at the same time, the rotational speed of the
driving motor 22 is controlled by the inverter 5.
[0037] Overall adiabatic efficiency and cooling capacity of the
screw compressor 50 will be described with reference to FIG. 3. In
FIG. 3, an axis of ordinate shows compressor efficiency and an axis
of abscissas shows refrigerating capacity ratio. An alternate long
and short dash line in the drawing indicates an efficiency curve by
the rotation control by the inverter, and a broken line indicates
an efficiency curve, in case where the rotational speed is changed
by the inverter and is fixed to respective rotational speeds and at
the same time, the capacity control is performed by the capacity
control valve. Note that a sold line in the drawing indicates an
efficiency curve in case where a control is performed such that the
rotational speed control by the inverter and the capacity control
by the capacity control valve are combined so as to reach the best
efficiency.
[0038] As apparent from FIG. 3, in the case of the screw compressor
50, in the present embodiment, combining the control by the
inverter 5 and the control by the capacity control valve 11, it is
possible to increase the compressor efficiency in the refrigerating
capacity ratio not more than 80%, and particularly in the region
where the refrigerating capacity ratio is low, it is possible to
sharply increase the compressor efficiency.
[0039] According to the invention, a screw compressor efficiently
operated as a screw chiller can be obtained.
[0040] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *