U.S. patent application number 17/298720 was filed with the patent office on 2022-02-17 for screw compressor.
The applicant listed for this patent is Hitachi Industrial Equipment Systems Co., Ltd.. Invention is credited to Kotaro CHIBA, Kenji MORITA, Masahiko TAKANO, Shigeyuki YORIKANE.
Application Number | 20220049700 17/298720 |
Document ID | / |
Family ID | 1000005989481 |
Filed Date | 2022-02-17 |
United States Patent
Application |
20220049700 |
Kind Code |
A1 |
CHIBA; Kotaro ; et
al. |
February 17, 2022 |
Screw Compressor
Abstract
A screw compressor is provided which can reduce the pressure
loss in a suction flow passage. A casing 12 of the screw compressor
includes a bore 21 that accommodates a lobed portion 13A of a male
rotor 11A and a lobed portion 13B of a female rotor 11B therein
such that working chambers are formed in lobe grooves of the lobed
portions, a suction port 22 located on an outer side in a rotor
radial direction, and a suction flow passage 23 that communicates
in a rotor axial direction with working chambers that are in a
suction stroke. The suction flow passage 23 includes a male rotor
side suction flow passage 26A located on an male rotor 11A side and
besides on a downstream side with respect to a virtual plane C, and
a female rotor side suction flow passage 26B located on an female
rotor 11B side and besides on the downstream side with respect to
the virtual plane C. The male rotor side suction flow passage 26A
is formed such that a flow passage wall 27A on the outer side in
the rotor radial direction is located at a position that is the
same as that of a wall of the bore 21 as viewed in the rotor axial
direction at least within a range of one half of an axial pitch P1
of the lobed portion 13A of the male rotor 11A from a suction side
end surface of the lobed portion 13A in the rotor axial
direction.
Inventors: |
CHIBA; Kotaro; (Tokyo,
JP) ; TAKANO; Masahiko; (Tokyo, JP) ;
YORIKANE; Shigeyuki; (Tokyo, JP) ; MORITA; Kenji;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi Industrial Equipment Systems Co., Ltd. |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Family ID: |
1000005989481 |
Appl. No.: |
17/298720 |
Filed: |
October 1, 2019 |
PCT Filed: |
October 1, 2019 |
PCT NO: |
PCT/JP2019/038674 |
371 Date: |
June 1, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04C 2240/30 20130101;
F04C 2240/20 20130101; F04C 18/16 20130101 |
International
Class: |
F04C 18/16 20060101
F04C018/16 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 4, 2018 |
JP |
2018- 227315 |
Claims
1. A screw compressor, comprising: a male rotor having a lobed
portion; a female rotor having a lobed portion that engages with
the lobed portion of the male rotor; and a casing that accommodates
the male rotor and the female rotor, the casing including a bore
that accommodates the lobed portion of the male rotor and the lobed
portion of the female rotor therein such that working chambers on a
male rotor side and working chambers on a female rotor side are
formed in lobe grooves of the lobed portions, a suction port
located on an outer side in a rotor radial direction with respect
to the lobed portion of the male rotor and the lobed portion of the
female rotor, and a suction flow passage formed so as to connect
the suction port to working chambers that are in a suction stroke
and communicating in a rotor axial direction with the working
chambers that are in the suction stroke, the suction flow passage
including a male rotor side suction flow passage located on the
male rotor side and besides on a downstream side with respect to a
virtual plane that passes a central axis of the male rotor and a
central axis of the female rotor, and a female rotor side suction
flow passage located on the female rotor side and besides on the
downstream side with respect to the virtual plane, wherein the male
rotor side suction flow passage is formed such that a flow passage
wall on the outer side in the rotor radial direction is located at
a position same as that of a wall of the bore as viewed in the
rotor axial direction at least within a range of one half of an
axial pitch of the lobed portion of the male rotor from a suction
side end surface of the lobed portion in the rotor axial
direction.
2. The screw compressor according to claim 1, wherein the male
rotor side suction flow passage is formed such that an area of each
flow passage cross section that is a rotor axial cross section
taken along each radial direction of the male rotor is same as an
area of a rotor radial cross section of each working chamber on the
male rotor side at least within a range of a rotational pitch of
the lobed portion of the male rotor from the virtual plane in a
direction of rotation of the male rotor.
3. The screw compressor according to claim 1, wherein the female
rotor side suction flow passage is formed such that a flow passage
wall on the outer side in the rotor radial direction is located at
a position same as that of the wall of the bore as viewed in the
rotor axial direction at least within a range of one half of an
axial pitch of the lobed portion of the female rotor from a suction
side end surface of the lobed portion in the rotor axial
direction.
4. The screw compressor according to claim 3, wherein the female
rotor side suction flow passage is formed such that an area of each
flow passage cross section that is a rotor axial cross section
taken along each radial direction of the female rotor is equal to
an area of a rotor radial cross section of each working chamber on
the female rotor side at least within a range of a rotational pitch
of the lobed portion of the female rotor from the virtual plane in
a direction of rotation of the female rotor.
5. A screw compressor comprising: a male rotor having a lobed
portion; a female rotor having a lobed portion that engages with
the lobed portion of the male rotor; and a casing that accommodates
the male rotor and the female rotor, the casing including a bore
that accommodates the lobed portion of the male rotor and the lobed
portion of the female rotor therein such that working chambers on a
male rotor side and working chambers on a female rotor side are
form in lobe grooves of the lobed portions, a suction port located
on an outer side in a rotor radial direction with respect to the
lobed portion of the male rotor and the lobed portion of the female
rotor, and a suction flow passage formed so as to connect the
suction port to working chambers that are in a suction stroke and
communicating in a rotor axial direction with the working chambers
that are in the suction stroke, the suction flow passage including
a male rotor side suction flow passage located on the male rotor
side and besides on a downstream side with respect to a virtual
plane that passes a central axis of the male rotor and a central
axis of the female rotor, and a female rotor side suction flow
passage located on the female rotor side and besides on the
downstream side with respect to the virtual plane, wherein the
female rotor side suction flow passage is formed such that a flow
passage wall on the outer side in the rotor radial direction is
located at a position same as that of a wall of the bore as viewed
in a rotor axial direction at least within a range of one half of
an axial pitch of the lobed portion of the male rotor from a
suction side end surface of the lobed portion in the rotor axial
direction.
6. The screw compressor according to claim 5, wherein the female
rotor side suction flow passage is formed such that an area of each
flow passage cross section that is a rotor axial cross section
taken along each radial direction of the female rotor is same as an
area of a rotor radial cross section of each working chamber on the
female rotor side at least within a range of a rotational pitch of
the lobed portion of the female rotor from the virtual plane in a
direction of rotation of the female rotor.
Description
TECHNICAL FIELD
[0001] The present invention relates to a screw compressor
including a suction port positioned on the outer side in a rotor
radial direction and a suction flow passage that communicates in a
rotor axial direction with a working chamber.
BACKGROUND ART
[0002] The screw compressor described in Patent Document 1 includes
a male rotor having a lobed portion, a female rotor having a lobed
portion that engages with the lobed portion of the male rotor, and
a casing that accommodates the male rotor and the female rotor
therein.
[0003] The casing has a bore that accommodates the lobed portion of
the male rotor and the lobed portion of the female rotor therein
such that working chambers on the male rotor side and working
chambers on the female rotor side are formed in lobe grooves of the
lobed portions. Further, the casing has a suction port located on
the outer side in a rotor radial direction with respect to the
lobed portion of the male rotor and the lobed portion of the female
rotor, and a suction flow passage formed so as to connect the
suction port to the working chambers that are in a suction stroke.
The casing further has a discharge port located on the outer side
in the rotor radial direction from the lobed portion of the male
rotor and the lobed portion of the female rotor, and a discharge
flow passage formed so as to connect the discharge port to the
working chambers that are in a discharge stroke.
[0004] The working chamber is changed in volume while moving from
one side to the other side in the rotor axial direction.
Consequently, the working chamber sequentially performs a suction
stroke for sucking gas from the suction port through the suction
flow passage, a compression stroke for compressing the gas, and a
discharge stroke for discharging the compressed gas to the
discharge port through the discharge flow passage.
[0005] The suction flow passage communicates in the rotor axial
direction with the working chambers that are in the suction stroke.
Further, the suction flow passage includes a male rotor side
suction flow passage provided on the male rotor side and besides on
the downstream side with respect to a virtual plane that passes a
central axis of the male rotor and a central axis of the female
rotor (in other words, on the opposite side to the suction port),
and a female rotor side suction flow passage provided on the female
rotor side and besides on the downstream side with respect to the
virtual plane described above.
PRIOR ART DOCUMENT
Patent Document
[0006] Patent Document 1: JP-2012-041910-A (for example, refer to
FIGS. 8 and 9)
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0007] In Patent Document 1, a flow passage wall on the outer side
in a rotor radial direction of the male rotor side suction flow
passage (except a portion for confining gas to the working chamber)
is located on the outer side in the rotor radial direction with
respect to the wall of the bore. Therefore, as a component of a
flow of the gas flowing from the male rotor side suction flow
passage toward the male rotor side working chamber, a component in
the rotor radial direction appears, and this makes a cause of
increase in pressure loss.
[0008] Similarly, a flow passage wall on the outer side, in a rotor
radial direction, of the female rotor side suction flow passage
(except a portion for confining gas to the working chamber) is
located on the outer side in the rotor radial direction with
respect to the wall of the bore. Therefore, as a component of a
flow of the gas flowing from the female rotor side suction flow
passage toward the female rotor side working chamber, a component
in the rotor radial direction appears, and this makes a cause of
increase in pressure loss.
[0009] The present invention has been made in view of such matters
as described above, and reducing the pressure loss in a suction
flow passage is one of subjects of the present invention.
Means for Solving the Problem
[0010] In order to solve the problem described above, the
configuration described in the claims is applied. The present
invention includes a plurality of means for solving the problem
described above, and an example of the means is a screw compressor
including a male rotor having a lobed portion; a female rotor
having a lobed portion that engages with the lobed portion of the
male rotor; and a casing that accommodates the male rotor and the
female rotor. The casing includes: a bore that accommodates the
lobed portion of the male rotor and the lobed portion of the female
rotor therein such that working chambers on a male rotor side and
working chambers on a female rotor side are formed in lobe grooves
of the lobed portions; a suction port located on an outer side in a
rotor radial direction with respect to the lobed portion of the
male rotor and the lobed portion of the female rotor; and a suction
flow passage formed so as to connect the suction port to working
chambers that are in a suction stroke and communicating in a rotor
axial direction with the working chambers that are in the suction
stroke. The suction flow passage includes: a male rotor side
suction flow passage located on the male rotor side and besides on
a downstream side with respect to a virtual plane that passes a
central axis of the male rotor and a central axis of the female
rotor; and a female rotor side suction flow passage located on the
female rotor side and besides on the downstream side with respect
to the virtual plane. The male rotor side suction flow passage is
formed such that a flow passage wall on the outer side in the rotor
radial direction is located at a position same as that of a wall of
the bore as viewed from the rotor axial direction at least within a
range of one half of an axial pitch of the lobed portion of the
male rotor from a suction side end surface of the lobed portion in
the rotor axial direction.
Advantage of the Invention
[0011] According to the present invention, the pressure loss in the
suction flow passage can be reduced.
[0012] It is to be noted that problems, configurations and
advantages other than those described above are made clear from the
following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic view depicting a configuration of a
screw compressor of the oil feeding type according to an embodiment
of the present invention.
[0014] FIG. 2 is a vertical sectional view depicting a structure of
a compressor main body in the embodiment of the present
invention.
[0015] FIG. 3 is a horizontal sectional view taken along line
III-III of FIG. 2.
[0016] FIG. 4 is a vertical sectional view taken along line IV-IV
of FIG. 2.
[0017] FIG. 5 is a vertical sectional view taken along line V-V of
FIG. 2.
[0018] FIG. 6 is a horizontal sectional view depicting a structure
of a compressor main body in a modification of the present
invention.
MODES FOR CARRYING OUT THE INVENTION
[0019] An embodiment of the present invention is described with
reference to FIGS. 1 to 5.
[0020] The screw compressor of the present embodiment includes a
motor 1, a compressor main body 2 driven by the motor 1 to compress
air (gas), a gas-liquid separator 3 that separates compressed air
discharged from the compressor main body 2 from oil (liquid)
included in the compressed air, and an oil pipe 4 that supplies the
oil separated by the gas-liquid separator 3 to the compressor main
body 2 (particularly, to working chambers, suction side bearings,
and discharge side bearings hereinafter described). The oil pipe 4
is provided with an oil cooler 5 for cooling the oil, an oil filter
6 for removing impurities in the oil, and so forth.
[0021] The compressor main body 2 includes a male rotor 11A and a
female rotor 11B that are screw rotors, and a casing 12 that
accommodates the male rotor 11A and the female rotor 11B
therein.
[0022] The male rotor 11A has a lobed portion 13A having a
plurality of (in the present embodiment, four) lobes extending
spirally, a suction side shaft portion 14A connected to one side
(left side in FIGS. 2 and 3) in an axial direction of the lobed
portion 13A, and a discharge side shaft portion 15A connected to
the other side (right side in FIGS. 2 and 3) in the axial direction
of the lobed portion 13A. The suction side shaft portion 14A of the
male rotor 11A is rotatably supported by a suction side bearing
16A, and the discharge side shaft portion 15A of the male rotor 11A
is rotatably supported on a discharge side bearing 17A.
[0023] Similarly, the female rotor 11B has a lobed portion 13B
having a plurality of (in the present embodiment, six) lobes
extending spirally, a suction side shaft portion 14B connected to
one side (left side in FIGS. 2 and 3), in the axial direction, of
the lobed portion 13B, and a discharge side shaft portion 15B
connected to the other side (right side in FIGS. 2 and 3), in the
axial direction, of the lobed portion 13B. The suction side shaft
portion 14B of the female rotor 11B is rotatably supported by a
suction side bearing 16B, and the discharge side shaft portion 15B
of the female portion 11B is rotatably supported by a discharge
side bearing 17B.
[0024] The suction side shaft portion 14A of the male rotor 11A
extends through the casing 12 and is coupled to a rotary shaft of
the motor 1. Thus, the male rotor 11A is rotated by driving of the
motor 1, and also the female rotor 11B is rotated through
engagement of the lobed portion 13A of the male rotor 11A and the
lobed portion 13B of the female rotor 11B.
[0025] The casing 12 is configured from a main casing 18, a suction
side casing 19 coupled to one side (left side in FIGS. 2 and 3), in
the axial direction, of the main casing 18 and a discharge side
casing 20 coupled to the opposite side (right side in FIGS. 2 and
3), in the axial direction, of the main casing 18.
[0026] The casing 12 has a bore 21 that accommodates the lobed
portion 13A of the male rotor 11A and the lobed portion 13B of the
female rotor 11B such that working chambers on the male rotor side
and working chambers on the female rotor side are formed in lobe
grooves of them. The bore 21 is configured such that two
cylindrical holes, in which the lobed portion 13A of the male rotor
11A and the lobed portion 13B of the female rotor 11B are
individually accommodated, partially overlap with each other.
[0027] The casing 12 has a suction port 22 located on the outer
side in a rotor radial direction (upper side in FIG. 2) with
respect to the lobed portion 13A of the male rotor 11A and the
lobed portion 13B of the female rotor 11B, and a suction flow
passage 23 formed so as to connect the suction port 22 to working
chambers that are in a suction stroke. The bore 21, suction port
22, and suction flow passage 23 are formed in the main casing
18.
[0028] The casing 12 has a discharge port 24 located on the outer
side (lower side in FIG. 2) in a rotor radial direction with
respect to the lobed portion 13A of the male rotor 11A and the
lobed portion 13B of the female rotor 11B, and a discharge flow
passage 25 formed so as to connect the discharge port to working
chambers that are in a discharge stroke. The discharge port 24 is
formed in the discharge side casing 20, and the discharge flow
passage 25 is formed in the discharge side casing 20 and the main
casing 18.
[0029] The working chamber is changed in volume while moving from
one side to the other side in the rotor axial direction.
Consequently, the working chamber sequentially performs a suction
stroke for sucking gas from the suction port 22 through the suction
flow passage 23, a compression stroke for compressing the gas, and
a discharge stroke for discharging the compressed gas to the
discharge port 24 through the discharge flow passage 25.
[0030] The suction flow passage 23 communicates in the rotor axial
direction with working chambers that are in the suction stroke.
Further, the suction flow passage 23 has a male rotor side suction
flow passage 26A located on the male rotor 11A side and besides on
the downstream side (in other words, on the opposite side to the
suction port 22) with respect to a virtual plane C that passes the
central axis O1 of the male rotor 11A and the central axis O2 of
the female rotor 11B, and a female rotor side suction flow passage
26B located on the female rotor 11B side and besides on the
downstream side with respect to the virtual plane C (refer to FIGS.
3 and 4).
[0031] Here, as a significant characteristic of the present
embodiment, a flow passage wall 27A on the outer side, in the rotor
radial direction, of the male rotor side suction flow passage 26A
(except a portion 28 for confining gas to the working chambers) is
formed such that it is located at a position that is the same as
that of a wall of the bore 21 as viewed in the rotor axial
direction at least within a range of one half of an axial pitch P1
(refer to FIG. 3) of the lobed portion 13A (as a particular
example, within a range of P1.times.0.8=R1 in FIG. 3, within a
range of P1.times.0.5=R1 in FIG. 6 hereinafter described) from a
suction side end surface of the lobed portion 13A of the male rotor
11A in the rotor axial direction. It is to be noted that the axial
pitch of the lobed portion signifies a distance between lobe tips
in the rotor axial direction. Further, since a working error and so
forth are taken into consideration, with regard to the flow passage
wall 27A, being at the same position as that of the wall of the
bore 21 when viewed in the rotor axial direction signifies that the
radial position of the flow passage wall 27A with reference to the
central axis O1 of the male rotor 11A falls within a range of 95%
to 105% of the radial position of the wall of the bore 21.
[0032] Further, a flow passage wall 27B on the outer side, in the
rotor radial direction, of the female rotor side suction flow
passage 26B (except the portion 28 for confining gas to the working
chambers) is formed such that it is located at a position that is
the same as that of the wall of the bore 21 as viewed in the rotor
axial direction at least within a range of one half of an axial
pitch P2 (P1=P2; refer to FIG. 3) of the lobed portion 13B from a
suction side end surface of the lobed portion 13B of the female
rotor 11B in the rotor axial direction (as a particular example, in
FIG. 3, within a range of P2.times.0.8=R2; in FIG. 6 hereinafter
described, within a range of P2.times.0.5=R2). It is to be noted
that, since a working error and so forth are taken into
consideration, with regard to the flow passage wall 27B, being at
the same position as that of the wall of the bore 21 as viewed in
the rotor axial direction signifies that the radial position of the
flow passage wall 27B with reference to the central axis O2 of the
female rotor 11B falls within a range of 95% to 105% of the radial
position of the wall of the bore 21.
[0033] In such an embodiment as described above, as a component of
a flow of gas flowing from the male rotor side suction flow passage
26A to the male rotor side working chamber, a component in the
rotor radial direction is less likely to appear, and therefore, the
pressure loss can be reduced. Further, since a component of the
rotor radial direction is less likely to appear as a component of a
flow of gas flowing from the female rotor side suction flow passage
26B to the female rotor side working chamber, the pressure loss can
be reduced. As a result, increase in the suction flow amount and
reduction of power can be achieved.
[0034] Further, in comparison with an alternative case in which the
flow passage walls 27A and 27B are located on the outer side in the
rotor radial direction with respect to the wall of the bore 21,
accumulating of oil into a lower portion of the male rotor side
suction flow passage 26A and the female rotor side suction flow
passage 26B at the time of stop of the compressor main body 2 can
be suppressed. Therefore, also the pressure loss by an influence of
oil accumulated in a lower portion of the male rotor side suction
flow passage 26A and the female rotor side suction flow passage 26B
can be suppressed.
[0035] Supplemental description is given to the reason why the
range within which the flow passage walls 27A and 27B are located
at the same position as that of the wall of the bore 21 as viewed
in the rotor axial direction is determined as a range of at least
one half of the axial pitch of the lobed portion of the rotor from
the suction side end surface of the lobed portion in the rotor
axial direction. From the point of view of the volume efficiency of
the screw compressor, it is necessary to take into consideration
the area of a rotor axial cross section of the male rotor side
suction flow passage 26A with respect to the area of a rotor axial
cross section of the male rotor side working chamber (in other
words, a cross section extending in the rotor axial direction) and
the area of the rotor axial cross section of the female rotor side
suction flow passage 26B with respect to the area of the rotor
axial cross section of the female rotor side working chamber. Since
the area of the rotor axial cross section of the male rotor side
working chamber is represented, for example, by (difference between
the outer diameter of the lobes of the male rotor and the outer
diameter of the shaft) x axial pitch 2, for the area of the rotor
axial cross section of the male rotor side suction flow passage
26A, it is better to assure at least (difference between the outer
diameter of the lobes of the male rotor and the outer diameter of
the shaft) x axial pitch=2. Similarly, since the area of the rotor
axial cross section of the female rotor side working chamber is
represented, for example, by (difference between the outer diameter
of the lobes of the female rotor and the outer diameter of the
shaft).times.axial pitch=2, for the area of the rotor axial cross
section of the female rotor side suction flow passage 26A, it is
better to assure at least (difference between the outer diameter of
the lobes of the female rotor and the outer diameter of the shaft)
x axial pitch=2. From such a point of view, if the male rotor side
suction flow passage 26A or the female rotor side suction flow
passage 26B does not have the characteristic within at least the
range of one half of the axial pitch of the lobed portion from the
suction side end surface of the lobed portion of the rotor in the
rotor axial direction, a sufficient advantage cannot be
obtained.
[0036] It is to be noted that, although the embodiment described
above is described taking as an example of a case in which the male
rotor side suction flow passage 26A is formed such that the area V1
(refer to FIG. 3) of each flow passage cross section that is a
rotor axial cross section taken along each radial direction of the
male rotor 11A is greater than the area S1 (refer to FIG. 5) of the
rotor radial cross section of each working chamber on the male
rotor side (in other words, a cross section extending in rotor
radial directions), and the female rotor side suction flow passage
26B is formed such that the area V2 (refer to FIG. 3) of each flow
passage cross section that is a rotor axial cross section taken
along each radial direction of the female rotor 11B is greater than
the area S2 (refer to FIG. 5) of the rotor radial cross section of
each working chamber on the female rotor side, this is not
restrictive. A modification of the present invention is described
with reference to FIG. 6. FIG. 6 is a horizontal sectional view
representing a structure of a compressor main body in the present
modification.
[0037] In the present modification, the male rotor side suction
flow passage 26A is formed such that the area V1 (refer to FIG. 6)
of each flow passage cross section that is a rotor axial cross
section taken along each radial direction of the male rotor 11A is
the same as the cross sectional area S1 (refer to FIG. 5) in a
rotor radial direction of each working chamber on the male water
side at least within a range of a rotational pitch (in the present
embodiment, 90 degrees) of the lobed portion 13A of the male rotor
11A from the virtual plane C in the direction of rotation of the
male rotor 11A. It is to be noted that the rotational pitch of the
lobed portion signifies an angle between adjacent lobe tips in the
direction of rotor rotation. Further, since a working error and so
forth are taken into consideration, the area V1 being the same as
the area S1 signifies that the area V1 falls within a range of 95%
to 105% of the area S1.
[0038] Meanwhile, the female rotor side suction flow passage 26B is
formed such that the area V2 (refer to FIG. 6) of each flow passage
cross section that is a rotor axial cross section taken along each
radial direction of the female rotor 11B is the same as the area S2
(refer to FIG. 5) of the rotor radial cross section of each working
chamber on the female rotor side at least within a range of the
rotational pitch (in the present embodiment, 45 degrees) of the
lobed portion 13B of the female rotor 11B from the virtual plane C
in the direction of rotation of the female rotor 11B. It is to be
noted that, since a working error and so forth are taken into
consideration, the area V2 being the same as the area S2 signifies
that the area V2 falls within a range of 95% to 105% of the area
S2.
[0039] In such a modification as described above, the change in the
flow velocity in the male rotor side suction flow passage 26A or
the change in the flow velocity from the male rotor side suction
flow passage 26A to the male rotor side working chamber can be
suppressed to further reduce the pressure loss. Further, the change
in the flow velocity in the female rotor side suction flow passage
26B or the change in the flow velocity from the female rotor side
suction flow passage 26B to the female rotor side working chamber
can be suppressed to further reduce the pressure loss.
[0040] It is to be noted that, although the foregoing description
of the embodiment is given taking as an example of a case in which
both the male rotor side suction flow passage 26A and the female
rotor side suction flow passage 26B have a first characteristic
(more particularly, the characteristic that the flow passage wall
on the outer side in the rotor radial direction is located at a
position that is the same as that of the wall of the bore 21 as
viewed in the rotor axial direction at least within the range of
one half of the axial pitch of the lobed portion from the suction
side end surface of the lobed portion in the rotor axial
direction), this is not restrictive. In particular, only one of the
male rotor side suction flow passage 26A and the female rotor side
suction flow passage 26B may have the first characteristic.
[0041] Further, although the foregoing description of the
modification is given taking as an example of a case in which both
the male rotor side suction flow passage 26A and the female rotor
side suction flow passage 26B have the first characteristic and a
second characteristic (more particularly, the characteristic that
they are formed such that the area of each flow passage cross
section that is a rotor axial cross section taken along each radial
direction of the rotor is the same as the area of the rotor radial
cross section of each working chamber at least within the range of
the rotational pitch of the lobed portion from the virtual plane C
in the direction of rotation of the rotor), this is not
restrictive. For example, only one of the male rotor side suction
flow passage 26A and the female rotor side suction flow passage 26B
may have the first characteristic and the second characteristic.
Further, for example, both the male rotor side suction flow passage
26A and the female rotor side suction flow passage 26B may have the
first characteristic while only one of the male rotor side suction
flow passage 26A and the female rotor side suction flow passage 26B
has the second characteristic.
[0042] Further, although the screw compressor of the oil feeding
type (more particularly, in which oil is supplied into the working
chambers) is taken as an example of the application target of the
present invention, this is not restrictive, and the application
target of the present invention may be a screw compressor of the
water feeding type (more particularly, in which water is supplied
into the working chambers) or a screw compressor of the no liquid
feeding type (more particularly, in which such liquid as oil or
water is not supplied into the working chambers).
DESCRIPTION OF REFERENCE CHARACTERS
[0043] 11A: Male rotor
[0044] 11B: Female rotor
[0045] 12: Casing
[0046] 13A, 13B: Lobed portion
[0047] 21: Bore
[0048] 22: Suction port
[0049] 23: Suction flow passage
[0050] 26A: Male rotor side suction flow passage
[0051] 26B: Female rotor side suction flow passage
[0052] 27A: Flow passage wall on the outer side, in the rotor
radial direction, of male rotor side suction flow passage
[0053] 27B: Flow passage wall on the outer side, in the rotor
radial direction, of female rotor side suction flow passage
* * * * *