U.S. patent application number 17/419356 was filed with the patent office on 2022-03-17 for screw compressor.
The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Masaaki KAMIKAWA, Masahiro KANDA, Shun OKADA.
Application Number | 20220082099 17/419356 |
Document ID | / |
Family ID | 1000006049686 |
Filed Date | 2022-03-17 |
United States Patent
Application |
20220082099 |
Kind Code |
A1 |
OKADA; Shun ; et
al. |
March 17, 2022 |
SCREW COMPRESSOR
Abstract
A screw compressor includes an internal-volume-ratio variable
mechanism including a variable Vi valve configured to make a Vi
value being an internal volume ratio variable. The screw compressor
controls a position of the variable Vi valve in two stages. The
position of the variable Vi valve when the Vi value is set to be
large is set to attain a Vi value with which a compressor
efficiency during operation under a predetermined high-load
condition or a predetermined high-compression-ratio condition is
equal to or higher than a set efficiency set in advance.
Inventors: |
OKADA; Shun; (Tokyo, JP)
; KAMIKAWA; Masaaki; (Tokyo, JP) ; KANDA;
Masahiro; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
1000006049686 |
Appl. No.: |
17/419356 |
Filed: |
March 1, 2019 |
PCT Filed: |
March 1, 2019 |
PCT NO: |
PCT/JP2019/008079 |
371 Date: |
June 29, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04C 18/16 20130101;
F04C 28/10 20130101 |
International
Class: |
F04C 18/16 20060101
F04C018/16; F04C 28/10 20060101 F04C028/10 |
Claims
1. A screw compressor comprising an internal-volume-ratio variable
mechanism including a variable Vi valve configured to make a Vi
value being an internal volume ratio variable, wherein the screw
compressor controls a position of the variable Vi valve in two
stages, and wherein, in an operation range of the compressor, the
position of the variable Vi valve when the Vi value is set to be
large is set to attain a Vi value with which a compressor
efficiency during operation under a predetermined high-load
condition or a predetermined high-compression-ratio condition is
equal to or higher than a set efficiency set in advance.
2. (canceled)
3. The screw compressor of claim 1, wherein the position of the
variable Vi valve when the Vi value is set to be small is set to
attain a Vi value with which a value obtained by multiplying each
of coefficients of performance at top one to top three operation
loads having large weights in a primary annual performance factor
calculated by applying weights for four operation loads, by the
weight corresponding to the operation load is equal to or greater
than a set value set in advance.
4. The screw compressor of claim 1, wherein the
internal-volume-ratio variable mechanism includes a piston coupled
to the variable Vi valve; and a cylinder configured to house the
piston, wherein inside of the cylinder is divided into two spatial
chambers by the piston, and wherein the two spatial chambers are
disposed as a cylinder chamber into which a discharge pressure is
normally introduced and a cylinder chamber into which a suction
pressure or a discharge pressure is introduced via a valve unit, in
order of closeness to the variable Vi valve.
5. The screw compressor of claim 1, wherein the
internal-volume-ratio variable mechanism includes a piston coupled
to the variable Vi valve; and a cylinder configured to house the
piston, wherein inside of the cylinder is divided into two spatial
chambers by the piston, and wherein the two spatial chambers are
disposed as a cylinder chamber into which a suction pressure or a
discharge pressure is introduced via a valve unit and a cylinder
chamber into which a suction pressure is normally introduced, in
order of closeness to the variable Vi valve.
6. The screw compressor of claim 1, wherein capacity control is
performed by inverter rotation speed control.
7. The screw compressor of claim 1, wherein the high-load condition
is a condition where the load is highest, and the
high-compression-ratio condition is a condition where the
compression ratio is largest.
8. The screw compressor of claim 1, wherein the set efficiency is
95% when the maximum efficiency is 100%.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a screw compressor used
for refrigerant compression in, for example, a refrigerator or an
air-conditioning apparatus.
BACKGROUND ART
[0002] Some screw compressors include a variable
internal-volume-ratio valve (hereinafter, referred to as a variable
Vi valve) that is a slide valve that adjusts the timing of
discharge start to make an internal volume ratio Vi variable, and
adjusts the opening degree of the variable Vi valve by a driving
force from a driving device depending on an operation compression
ratio (for example, see Patent Literature 1). The internal volume
ratio in the screw compressor is a ratio between a tooth groove
space volume at the time of suction and a tooth groove space volume
immediately before discharge, and represents a ratio between a
volume when the suction is completed and a volume when a discharge
port is opened.
[0003] As illustrated in FIGS. 1 and 2 of Patent Literature 1, the
variable Vi valve of Patent Literature 1 is controlled such that
the difference between an optimum Vi value calculated from a
discharge pressure HP and a suction pressure LP and a current Vi
value obtained from a position detecting unit decreases. To bring
the Vi value close to the optimum Vi value in actual operation, the
opening degree of the variable Vi valve is adjusted to minimize
motor driving power.
[0004] The screw compressor has an appropriate compression ratio
corresponding to the internal volume ratio, and an inappropriate
compression loss is not generated under an operating condition
where the compression ratio at the time of actual operation is the
appropriate compression ratio. However, when the operation is
performed at a low compression ratio lower than the appropriate
compression ratio, gas is excessively compressed to a pressure
equal to or higher than a discharge pressure before the discharge
port opens, and excessive compression work is performed. In
contrast, when the operation is performed at a high compression
ratio higher than the appropriate compression ratio, the discharge
port opens before the pressure reaches the discharge pressure,
causing a state of insufficient compression in which backflow of
gas is generated. Both of the operation at the low compression
ratio and the operation at the high compression ratio cause a loss
of power and cause a decrease in efficiency.
[0005] Thus, as in Patent Literature 1, a technique has been
proposed in which the internal volume ratio is made variable by
steplessly adjusting the position of the variable Vi valve to
attain the internal volume ratio at which a high compressor
efficiency is obtained for a compression ratio (discharge
pressure/suction pressure) depending on an operation load.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: Japanese Patent No. 4147891
SUMMARY OF INVENTION
Technical Problem
[0007] In Patent Literature 1, position control of the variable Vi
valve is steplessly performed, and a control amount of the variable
Vi valve is calculated from detection results of a discharge
pressure, a suction pressure, and a rotation frequency. That is, in
Patent Literature 1, the position control of the variable Vi valve
is stepless control, and hence the configuration and control are
complicated.
[0008] The present disclosure has been made to address the
above-described problems, and an object of the present disclosure
is to obtain a screw compressor whose configuration and control can
be simplified while an internal volume ratio is made variable.
Solution to Problem
[0009] A screw compressor of an embodiment of the present
disclosure includes an internal-volume-ratio variable mechanism
including a variable Vi valve configured to make a Vi value being
an internal volume ratio variable. The screw compressor controls a
position of the variable Vi valve in two stages. The position of
the variable Vi valve when the Vi value is set to be large is set
to attain a Vi value with which a compressor efficiency during
operation under a predetermined high-load condition or a
predetermined high-compression-ratio condition is equal to or
higher than a set efficiency set in advance.
Advantageous Effects of Invention
[0010] With the embodiment of the present disclosure, since the
position control of the variable Vi valve is performed in the two
stages, the configuration and control can be simplified while the
internal volume ratio is made variable.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a general configuration diagram of a screw
compressor according to Embodiment 1 of the present disclosure.
[0012] FIG. 2 is a schematic diagram of an internal-volume-ratio
variable mechanism including a driving device for the screw
compressor according to Embodiment 1 of the present disclosure.
[0013] FIG. 3 is an operation schematic diagram when a Vi value is
large in the screw compressor according to Embodiment 1 of the
present disclosure.
[0014] FIG. 4 is an operation schematic diagram when a Vi value is
small in the screw compressor according to Embodiment 1 of the
present disclosure.
[0015] FIG. 5 is an operation schematic diagram when a Vi value is
large in the screw compressor according to Embodiment 2 of the
present disclosure.
[0016] FIG. 6 is an operation schematic diagram when a Vi value is
small in the screw compressor according to Embodiment 2 of the
present disclosure.
[0017] FIG. 7 illustrates a modification of the screw compressor
according to any one of Embodiment 1 and Embodiment 2 of the
present disclosure.
DESCRIPTION OF EMBODIMENTS
Embodiment 1
[0018] FIG. 1 is a general configuration diagram of a screw
compressor according to Embodiment 1 of the present disclosure.
[0019] The screw compressor according to Embodiment 1 is a single
screw compressor, and as schematically illustrated in FIG. 1, the
screw compressor includes a cylindrical casing main body 1, a screw
rotor 3 housed in the casing main body 1, and a motor 2 that
rotatably drives the screw rotor 3. The motor 2 includes a stator
2a that is secured in contact with the inside of the casing main
body 1 and a motor rotor 2b that is disposed inside the stator 2a.
The rotation speed of the motor 2 is controlled by an inverter
method. The capacity control for operating the screw compressor at
a desired operation compression ratio may be implemented through
rotation speed control by driving the motor 2 with an inverter.
[0020] The screw rotor 3 and the motor rotor 2b are disposed on the
same axis, and both are secured to a screw shaft 4. A plurality of
helical grooves (hereinafter referred to as screw grooves) 3a are
formed in the outer peripheral surface of the screw rotor 3. The
screw rotor 3 is coupled to and rotatably driven by the motor rotor
2b secured to the screw shaft 4. The space in the screw grooves 3a
formed in the screw rotor 3 is surrounded by the inner cylindrical
surface of the casing main body 1 and a pair of gate rotors (not
illustrated) that mesh with and are engaged with the grooves to
define a compression chamber 5.
[0021] In the casing main body 1, a discharge pressure side and a
suction pressure side are separated from each other by a separation
wall (not illustrated). A discharge chamber 6 and a discharge port
7 that opens to the discharge chamber 6 are formed on the discharge
pressure side. In the casing main body 1, a suction chamber 16 is
formed on the suction pressure side. The casing main body 1 is
further provided with a pair of variable Vi valves 8 that are
coupled to a pair of rods 9 and a pair of driving devices 10 and
are movable in the axial direction. The variable Vi valves 8 define
part of the discharge port 7. Illustration of the driving device 10
coupled to the other variable Vi valve 8 is omitted.
[0022] FIG. 2 is a schematic diagram of an internal-volume-ratio
variable mechanism including a driving device for the screw
compressor according to Embodiment 1 of the present disclosure.
[0023] The driving device 10 forms part of an internal-volume-ratio
variable mechanism (hereinafter, referred to as a variable Vi
mechanism), and is configured to couple a piston 12 provided in a
cylinder 11 and the variable Vi valve 8 to each other by the rod
9.
[0024] The variable Vi valve 8 includes a valve main body 8a, a
guide portion 8b, and a coupling portion 8c. The coupling portion
8c is provided at a discharge-port-side end portion 8e of the guide
portion 8b. The rod 9 is coupled to an end surface of the guide
portion 8b on the side near the driving device 10. The
discharge-port-side end portion 8d of the valve main body 8a and a
discharge-port-side end portion 8e of the guide portion 8b are
coupled to each other by the coupling portion 8c, and the gap
therebetween serves as a discharge gap 8f communicating with the
discharge port 7.
[0025] The inside of the cylinder 11 is partitioned into two
spatial chambers by the piston 12. A cylinder chamber 13a is formed
on the front side (on the side of the variable Vi valve) of the
piston 12, and a cylinder chamber 13b is formed on the rear side
(on the side opposite to the variable Vi valve) of the piston 12.
The cylinder 11 has a pressure introduction hole 113a provided on
the cylinder chamber 13a side close to the variable Vi valve 8. The
cylinder 11 also has a pressure introduction hole 113b provided on
the cylinder chamber 13b side far from the variable Vi valve 8.
[0026] The cylinder chamber 13a communicates with the discharge
chamber 6 illustrated in FIG. 1 via the pressure introduction hole
113a and a flow path 15a, and a discharge pressure is normally
introduced into the cylinder chamber 13a. The cylinder chamber 13b
communicates with the discharge chamber 6 illustrated in FIG. 1
through the pressure introduction hole 113b and a flow path 15b and
communicates with the suction chamber 16 illustrated in FIG. 1
through a flow path 15c branched from the middle of the flow path
15b. The flow path 15b is provided with a solenoid valve 14b that
opens and closes the flow path 15b, and the flow path 15c is
provided with a solenoid valve 14a that opens and closes the flow
path 15c. A discharge pressure or a suction pressure is selectively
introduced into the cylinder chamber 13b by opening and closing of
the solenoid valve 14a and the solenoid valve 14b.
[0027] The solenoid valve 14a and the solenoid valve 14b described
above are examples, and each may be any valve unit that is capable
of opening and closing a flow path or switching flow paths. For
example, the solenoid valve 14a and the solenoid valve 14b each may
be a stop valve or a three-way valve. In the case of a three-way
valve capable of switching flow paths, it is sufficient that one
three-way valve is provided at a branch portion of the flow paths,
and thus the solenoid valve 14a and the solenoid valve 14b may be
omitted. The flow path 15a, the flow path 15b, and the flow path
15c may be formed inside the wall of the casing main body 1 and the
wall of the cylinder 11, or may be connected by using a pipe.
[0028] Next, the operation of the variable Vi valve 8 will be
described. With this variable Vi mechanism, the Vi value can be set
to two values of a large value and a small value.
(i) Operation when Vi Value is Large
[0029] FIG. 3 is an operation schematic diagram when a Vi value is
large in the screw compressor according to Embodiment 1 of the
present disclosure.
[0030] When the Vi value is large, the driving device 10 positions
the variable Vi valve 8 in the left direction represented by the
arrow in the drawing, thereby delaying the timing at which the
discharge port 7 opens.
[0031] That is, when the Vi value is large, the solenoid valve 14a
is opened and the solenoid valve 14b is closed so that the pressure
in the cylinder chamber 13b is a suction pressure. In contrast, the
cylinder chamber 13a is coupled to the discharge chamber 6, and a
discharge pressure is normally introduced into the cylinder chamber
13a. Hence, the piston 12 is to move in the left direction in the
drawing due to the pressure difference in the cylinder 11.
[0032] In the variable Vi valve 8 coupled to the piston 12, a
suction pressure acts on a suction-side end portion 8g of the valve
main body 8a, and a discharge pressure immediately after discharge
acts on the discharge-port-side end portion 8d. The same pressure
as the pressure acting on the discharge-port-side end portion 8d
acts on the discharge-port-side end portion 8e of the guide portion
8b in directions opposite to each other. A discharge pressure acts
on a driving-device-side end portion 8h of the guide portion 8b.
Thus, the loads acting on the discharge-port-side end portion 8d
and the discharge-port-side end portion 8e in the variable Vi valve
8 cancel out each other. Hence, the variable Vi valve 8 is to move
in the right direction in the drawing due to the pressure
difference between the pressure acting on the driving-device-side
end portion 8h and the pressure acting on the suction-side end
portion 8g.
[0033] In this case, the area of each of both end surfaces in the
movement direction of the piston 12 is set to be larger than the
area of the driving-device-side end portion 8h of the variable Vi
valve 8. Thus, the piston 12 and the variable Vi valve 8 move in
the left direction in the drawing due to the pressure difference
received in both the areas. Since the variable Vi valve 8 stops at
a position at which the piston 12 abuts against the wall surface of
the cylinder chamber 13, the variable Vi valve 8 is accurately
positioned at a position at which the Vi value is large.
(ii) Operation when Vi Value Is Small
[0034] FIG. 4 is an operation schematic diagram when the Vi value
is small in the screw compressor according to Embodiment 1 of the
present disclosure.
[0035] When the Vi value is small, the driving device 10 positions
the variable Vi valve 8 in the right direction represented by the
arrow in the drawing, thereby advancing the timing at which the
discharge port 7 opens.
[0036] That is, when the Vi value is small, the solenoid valve 14a
is closed and the solenoid valve 14b is opened so that the pressure
in the cylinder chamber 13b is a discharge pressure. In contrast,
since the cylinder chamber 13a is coupled to the discharge chamber
6 and a discharge pressure is normally introduced into the cylinder
chamber 13a, there is no pressure difference in the cylinder
chamber 13.
[0037] In the variable Vi valve 8 coupled to the piston 12, a
suction pressure acts on the suction-side end portion 8g of the
valve main body 8a, and a discharge pressure immediately after
discharge acts on the discharge-port-side end portion 8d. The same
pressure as the pressure acting on the discharge-port-side end
portion 8d acts on the discharge-port-side end portion 8e of the
guide portion 8b in directions opposite to each other. A discharge
pressure acts on the driving-device-side end portion 8h of the
guide portion 8b.
[0038] Thus, the variable Vi valve 8 moves in the right direction
in the drawing due to the pressure difference between the discharge
pressure acting on the driving-device-side end portion 8h and the
suction pressure acting on the suction-side end portion 8g. Since
the variable Vi valve 8 stops at a position at which the piston 12
abuts against the wall surface of the cylinder chamber 13, the
variable Vi valve 8 is accurately positioned at a position at which
the Vi value is small. Alternatively, as illustrated in FIG. 1, the
variable Vi valve 8 may be positioned at a position where the
suction-side end portion 8g of the variable Vi valve 8 abuts
against the wall surface of the casing main body 1.
[0039] Setting of the Vi value will be described. For setting of
the Vi value, there are a policy for setting to secure a wide
operation range and a policy for setting to improve "rated
performance" or "primary annual performance factor" which is one of
indexes of energy saving. Setting methods based on the respective
policies will be described below.
(Securing Wide Operation Range)
[0040] To secure a wide operation range, the large-side Vi value
may be set as follows. To protect the compressor, the operation
range is set, for example, by setting an upper limit temperature
for the temperature of discharged refrigerant gas, the temperature
of windings of the motor stator, or another temperature. When the
evaporating temperature is constant, increasing the condensing
temperature as high as possible in a range lower than the upper
limit temperature leads to securing a wide operation range. In
contrast, when the condensing temperature is constant, making the
evaporating temperature as low or as high as possible leads to
securing a wide operation range.
[0041] The temperature of the discharged refrigerant gas is likely
to increase during operation under a high-compression-ratio
condition, and the winding temperature is likely to increase under
a high-load condition or a high-compression-ratio condition. The
high-compression-ratio condition involves conditions including a
high condensing temperature and a low evaporating temperature. The
high-load condition involves conditions including a high condensing
temperature and a high evaporating temperature. Thus, when the
temperature of the discharged refrigerant gas and the winding
temperature are about to reach the upper limit temperatures during
operation under the high-load condition or the
high-compression-ratio condition, the operation has to be changed
such that the temperature of the discharged refrigerant gas and the
winding temperature do not reach the upper limit temperatures. To
change the operation, for example, a measure such as reducing the
rotation speed of the compressor to decrease the condensing
temperature has to be taken so that the operating temperature
condition falls within the operation range. That is, when it is
desired to continue the operation while keeping the condensing
temperature high, the temperature of the discharged refrigerant gas
and the winding temperature increase during operation under the
high-load condition or the high-compression-ratio condition. Thus,
a measure such as decreasing the condensing temperature is
required, and the operation range is narrowed.
[0042] The temperature of the discharged refrigerant gas and the
winding temperature under a certain operating condition tend to
decrease as the compressor efficiency under the operating condition
increases. Thus, by increasing the compressor efficiency during
operation under the high-load condition or the
high-compression-ratio condition, it is possible to suppress
increases in the temperature of the discharged refrigerant gas and
the winding temperature without taking a measure such as decreasing
the condensing temperature. Consequently, this leads to securing of
a wide operation range. The compressor efficiency is determined by
the internal structure of the compressor and structural elements
such as the number of winding turns of the motor.
[0043] The large-side Vi value is set to a Vi value with which the
compressor efficiency is equal to or higher than a set efficiency
set in advance during operation under a predetermined high-load
condition or a predetermined high-compression-ratio condition. The
compressor efficiency is a value that changes depending on the Vi
value, and is expressed by a graph that projects upward when the
horizontal axis represents Vi and the vertical axis represents the
compressor efficiency. That is, there is a Vi value with which the
compressor efficiency is the maximum. Based on this, the large-side
Vi value may be the Vi value when the compressor efficiency is the
maximum, or in other words, only has to be set to a value with
which the compressor efficiency is equal to or higher than the set
efficiency. The set efficiency only has to be appropriately set
depending on performance or another factor required for the screw
compressor. For example, when the maximum efficiency is 100%, the
set efficiency may be 95% or more.
[0044] In a case where a screw compressor that secures a wide
operation range is configured, the Vi value is set as described
above. Thus, the position when the variable Vi valve 8 is moved to
the side where the Vi value is large is set to attain the set Vi
value.
(Improvement in Rated Performance or Primary Annual Performance
Factor)
[Improvement in Rated Performance: Large-Side Vi Value]
[0045] The large-side Vi value is set so that the rated performance
is improved. The rated performance is performance under conditions
defined by industrial standards or other standards, and represents
the performance of the compressor. The rated performance is a value
that changes depending on the Vi value, and is represented by a
graph that projects upward when the horizontal axis represents Vi
and the vertical axis represents the rated performance. That is,
there is a Vi value with which the rated performance is the
maximum. Based on this, the large-side Vi value may be the Vi value
when the rated performance is the maximum, or in other words, only
has to be set to a Vi value with which the rated performance is
equal to or higher than a set performance set in advance. The set
performance only has to be appropriately set depending on
performance or another factor required for the screw compressor.
For example, when the maximum performance is 100%, the set
performance may be 95% or more.
[0046] In a case where a screw compressor aiming at improvement in
the rated performance is configured, the Vi value is set as
described above. Thus, the position when the variable Vi valve 8 is
moved to the side where the Vi value is large is set to attain the
set Vi value.
[Improvement in Primary Annual Performance Factor Small-Side Vi
Value]
[0047] The small-side Vi value is set as follows. In the
refrigerating and air-conditioning apparatus, in addition to a
coefficient of performance called COP representing energy
consumption efficiency, there is a coefficient of performance for a
refrigerator throughout a year such as an integrated part load
value (IPLV) or an European seasonal energy efficiency ratio
(ESEER).
[0048] In the Air-Conditioning and Refrigeration Institute (ARI),
an IPLV that is a primary annual performance factor is calculated
by the following formula.
IPLV=0.01.times.A+0.42.times.B+0.45.times.C+0.12.times.D [0049]
A=COP at 100% load, B=COP at 75% load, [0050] C=COP at 50% load,
D=COP at 25% load
[0051] With this formula, the weight to be multiplied differs
depending on the load during operation. Of the annual operation
period of the refrigerating and air-conditioning apparatus,
operation at 75% load accounts for 42%, and operation at 50% load
accounts for 45%. Thus, the weights for the two conditions are
large in the formula of the IPLV.
[0052] Indexes are defined similarly in the Japan Refrigeration and
Air Conditioning Industry Association (JRAIA) and
EUROVENT/CECOMAF.
[0053] In the case of the Japan Refrigeration and Air Conditioning
Industry Association (JRAIA), an IPLV is defined as the following
formula.
IPLV=0.01.times.A+0.47.times.B+0.37.times.C+0.15.times.D [0054]
A=COP at 100% load, B=COP at 75% load, [0055] C=COP at 50% load,
D=COP at 25% load
[0056] In the case of EUROVENT/CECOMAF, an ESEER is defined as an
European seasonal energy efficiency ratio. Like the IPLV, the ESEER
is a value obtained by multiplying an energy efficiency ratio of
four operation load conditions by a weighting factor, and is
calculated by the following formula. For the calculation of the
ESEER, an energy efficiency ratio (EER) that is a value
representing an energy consumption efficiency is used as in the
case of the COP.
ESEER=0.03.times.A+0.33.times.B+0.41.times.C+0.23.times.D [0057]
A=EER at 100% load, B=EER at 75% load, [0058] C=EER at 50% load,
D=EER at 25% load
[0059] As described above, the weight at 75% load and the weight at
50% load are large for various indexes representing the
coefficients of performance throughout a year of the refrigerating
and air-conditioning apparatus.
[0060] Here, describing with an example of the formula of the Japan
Refrigeration and Air Conditioning Industry Association (JRAIA),
"0.01.times.A" may be a coefficient of performance in 100% load
operation, and "0.47.times.B+0.37.times.C+0.15.times.D" may be a
coefficient of performance in partial load operation.
[0061] The small-side Vi value is set to perform efficient
operation in partial load operation, and is set to a Vi value with
which the value of "0.47.times.B+0.37.times.C+0.15.times.D" is
equal to or greater than a set value set in advance. In other
words, the small-side Vi value is set based on the top three
operation loads having large weights in the primary annual
performance factor.
[0062] The value of "0.47.times.B+0.37.times.C+0.15.times.D" is a
value that changes depending on the Vi value, and is represented by
a graph that projects upward when the horizontal axis represents Vi
and the vertical axis represents
"0.47.times.B+0.37.times.C+0.15.times.D". That is, there is a Vi
value with which the value of
"0.47.times.B+0.37.times.C+0.15.times.D" is the maximum. Based on
this, the small-side Vi value may be the Vi value when
"0.47.times.B+0.37.times.C+0.15.times.D" is the maximum, or in
other words, only has to be a value that is equal to or greater
than the set value. The set value only has to be appropriately set
depending on performance or another factor required for the screw
compressor. For example, when the maximum set value is 100%, the
set value may be 95% or more.
[0063] When a screw compressor that performs efficient operation in
partial load operation is configured, the Vi value is set as
described above. Thus, the position when the variable Vi valve 8 is
moved to attain the small-side Vi value is set to attain the set Vi
value.
[0064] When the small-side Vi value is set as described above and
the large-side Vi value is set to a Vi value with which the
compressor efficiency is equal to or higher than the set efficiency
during operation under the high-load condition or the
high-compression-ratio condition, a wide operation range can be
secured and the IPLV can be improved.
[0065] When the small-side Vi value is set as described above and
the larger-side Vi value is set to a Vi value with which the rated
performance is equal to or higher than the set performance during
operation under the rated condition, both the rated performance and
the IPLV can be improved.
[0066] It is determined that the small-side Vi value is set based
on the top three operation loads having large weights in the
primary annual performance factor. However, as described above,
operation at 75% load and operation at 50% load account for the
majority of operation period per year. Thus, the small-side Vi
value may be set based on the top one or top two operation loads
having large weights in the primary annual performance factor.
[0067] As described above, in Embodiment 1, the variable Vi valve
is controlled under the simple two-stage control based on only the
discharge pressure and the suction pressure. Thus, the
configuration and control can be simplified without necessity of a
special device while the internal volume ratio is made
variable.
[0068] The position of the variable Vi valve when the Vi value is
set to be large is set to attain the Vi value with which the
compressor efficiency is equal to or higher than the set efficiency
during operation under the high-load condition or the
high-compression-ratio condition. Thus, a wide operation range can
be secured.
[0069] The position of the variable Vi valve when the Vi value is
set to be large is set to attain the Vi value with which the rated
performance is equal to or higher than the set performance. Thus,
the rated performance can be improved.
[0070] The position of the variable Vi valve when the Vi value is
set to be small is set to attain the Vi value with which a value
obtained by multiplying each of the coefficients of performance at
the top one to top three operation loads by the weight
corresponding to the operation load is equal to or greater than the
set value. This can improve the partial load performance and
improve the compressor efficiency.
Embodiment 2
[0071] Embodiment 1 provides the configuration in which the
pressure introduction hole 113a of the cylinder chamber 13a is
coupled to the discharge chamber 6. Embodiment 1 also provides the
configuration in which the pressure introduction hole 113b of the
cylinder chamber 13b is coupled to the discharge chamber 6 in the
casing main body 1 through the flow path 15b via the solenoid valve
14b, and is coupled to the suction chamber 16 in the casing main
body 1 through the flow path 15c via the solenoid valve 14a.
Embodiment 2 has a configuration in which the pressure introduction
hole 113a is coupled to the discharge chamber 6 in the casing main
body 1 through the flow path 15b via the solenoid valve 14b, and is
coupled to the suction chamber 16 in the casing main body 1 through
the flow path 15c via the solenoid valve 14a. The pressure
introduction hole 113b is coupled to the suction chamber 16 in the
casing main body 1.
[0072] Next, the operation of the variable Vi valve 8 according to
Embodiment 2 will be described. As in Embodiment 1, the Vi value
can be set to two values of a large value and a small value.
(i) Operation when Vi Value is Large
[0073] FIG. 5 is an operation schematic diagram when a Vi value is
large in the screw compressor according to Embodiment 2 of the
present disclosure.
[0074] When the Vi value is large, the driving device 10 positions
the variable Vi valve 8 in the left direction represented by the
arrow in the drawing, thereby delaying the timing at which the
discharge port 7 opens.
[0075] That is, when the Vi value is large, the solenoid valve 14a
is closed and the solenoid valve 14b is opened so that the pressure
in the cylinder chamber 13a is a discharge pressure. In contrast,
the cylinder chamber 13b is coupled to the suction chamber 16, and
a suction pressure is normally introduced into the cylinder chamber
13b. Hence, the piston 12 is to move in the left direction in the
drawing due to the pressure difference in the cylinder chamber
13.
[0076] In the variable Vi valve 8 coupled to the piston 12, a
suction pressure acts on the suction-side end portion 8g of the
valve main body 8a, and a discharge pressure immediately after
discharge acts on the discharge-port-side end portion 8d. The same
pressure as the pressure acting on the discharge-port-side end
portion 8d acts on the discharge-port-side end portion 8e of the
guide portion 8b in directions opposite to each other. A discharge
pressure acts on the driving-device-side end portion 8h of the
guide portion 8b.
[0077] Thus, the loads acting on the discharge-port-side end
portions 8d and 8e in the variable Vi valve 8 cancel out each
other. Hence, the variable Vi valve 8 is to move in the right
direction in the drawing due to the pressure difference between the
pressure acting on the driving-device-side end portion 8h and the
pressure acting on the suction-side end portion 8g. However, since
the area of each of both end surfaces of the piston 12 in the
movement direction is set to be larger than the area of the
driving-device-side end portion 8h of the variable Vi valve 8, the
piston 12 and the variable Vi valve 8 move in the left direction in
the drawing due to the pressure difference received in both the
areas. Since the variable Vi valve 8 stops at a position at which
the piston 12 abuts against the wall surface of the cylinder
chamber 13, the variable Vi valve 8 is accurately positioned at a
position at which the Vi value is large.
(ii) Operation when Vi Value is Small
[0078] FIG. 6 is an operation schematic diagram when the Vi value
is small in the screw compressor according to Embodiment 2 of the
present disclosure.
[0079] When the Vi value is small, the driving device 10 positions
the variable Vi valve 8 in the right direction represented by the
arrow in the drawing, thereby advancing the timing at which the
discharge port 7 opens.
[0080] That is, when the Vi value is small, the solenoid valve 14a
is opened and the solenoid valve 14b is closed so that the pressure
in the cylinder chamber 13a is a suction pressure. In contrast,
since the cylinder chamber 13b is coupled to the suction chamber 16
and a suction pressure is normally introduced into the cylinder
chamber 13b, there is no pressure difference in the cylinder
chamber 13.
[0081] In the variable Vi valve 8 coupled to the piston 12, a
suction pressure acts on the suction-side end portion 8g of the
valve main body 8a, and a discharge pressure immediately after
discharge acts on the discharge-port-side end portion 8d. The same
pressure as the pressure acting on the discharge-port-side end
portion 8d acts on the discharge-port-side end portion 8e of the
guide portion 8b in directions opposite to each other. A discharge
pressure acts on the driving-device-side end portion 8h of the
guide portion 8b.
[0082] Thus, the variable Vi valve 8 moves in the right direction
in the drawing due to the pressure difference between the discharge
pressure acting on the driving-device-side end portion 8h and the
suction pressure acting on the suction-side end portion 8g. Since
the variable Vi valve 8 stops at a position at which the piston 12
abuts against the wall surface of the cylinder chamber 13, the
variable Vi valve 8 is accurately positioned at a position at which
the Vi value is small. Alternatively, as illustrated in FIG. 1, the
variable Vi valve 8 may be positioned at a position where the
suction-side end portion 8g of the variable Vi valve 8 abuts
against the wall surface of the casing main body 1.
[0083] According to Embodiment 2, effects similar to those of
Embodiment 1 can be obtained.
[0084] The screw compressor according to the present disclosure is
not limited to those illustrated in FIGS. 1 to 6, and may be
modified and implemented, for example, as described below within
the scope not departing from the gist of the present
disclosure.
[0085] FIG. 7 illustrates a modification of the screw compressor
according to any one of Embodiment 1 and Embodiment 2 of the
present disclosure.
[0086] In this modification, the piston 12 illustrated in FIG. 1 is
omitted, and a piston rod 17 is provided. In FIG. 1, there is one
piston for one variable Vi valve. In contrast, in this
modification, the piston rod 17 is coupled to rods 9 of two
variable Vi valves 8 via a common attachment plate 18, and the one
piston rod 17 is provided for the two variable Vi valves 8. As
described above, the number of pistons 12 for the variable Vi
valves 8 is not limited.
REFERENCE SIGNS LIST
[0087] 1: casing main body, 2: motor, 2a: stator, 2b: motor rotor,
3: screw rotor, 3a: screw groove, 4: screw shaft, 5: compression
chamber, 6: discharge chamber, 7: discharge port, 8: variable Vi
valve, 8a: valve main body, 8b: guide portion, 8c: coupling
portion, 8d: discharge-port-side end portion, 8e:
discharge-port-side end portion, 8f: discharge gap, 8g:
suction-side end portion, 8h: driving-device-side end portion, 9:
rod, 10: driving device, 11: cylinder, 12: piston, 13: cylinder
chamber, 13a cylinder chamber, 13b: cylinder chamber, 14a: solenoid
valve, 14b: solenoid valve, 15a: flow path, 15b: flow path, 15c:
flow path, 16: suction chamber, 17: piston rod, 18: attachment
plate, 113a: pressure introduction hole, 113b: pressure
introduction hole
* * * * *