U.S. patent application number 11/989241 was filed with the patent office on 2010-05-27 for centrifugal compressor.
Invention is credited to Hirotaka Higashimori, Hideyoshi Isobe, Takashi Shiraishi, Koichi Sugimoto.
Application Number | 20100129209 11/989241 |
Document ID | / |
Family ID | 39200296 |
Filed Date | 2010-05-27 |
United States Patent
Application |
20100129209 |
Kind Code |
A1 |
Sugimoto; Koichi ; et
al. |
May 27, 2010 |
Centrifugal Compressor
Abstract
There is provided a centrifugal compressor having a diffuser
structure in which airflow is unlikely to separate from a hub side
wall surface on a hub side wall surface downstream side within a
diffuser passage. In a centrifugal compressor provided with a
diffuser passage 15 for recovering static pressure by slowing down
discharged air from an outer circumferential end of an impeller
that rotates within a housing 11, a hub side wall surface 15b of
the diffuser passage 15 is provided with an inclined plane 20 that
approaches toward a shroud side, in a position on a downstream side
of a portion parallel with a normal line direction of a section
surface of an impeller exit.
Inventors: |
Sugimoto; Koichi; (Nagasaki,
JP) ; Shiraishi; Takashi; (Kanagawa, JP) ;
Higashimori; Hirotaka; (Nagasaki, JP) ; Isobe;
Hideyoshi; (Nagasaki, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
39200296 |
Appl. No.: |
11/989241 |
Filed: |
February 9, 2007 |
PCT Filed: |
February 9, 2007 |
PCT NO: |
PCT/JP2007/052391 |
371 Date: |
March 7, 2008 |
Current U.S.
Class: |
415/203 |
Current CPC
Class: |
F04D 29/441
20130101 |
Class at
Publication: |
415/203 |
International
Class: |
F04D 29/44 20060101
F04D029/44 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2006 |
JP |
2006-255383 |
Claims
1. A centrifugal compressor provided with a diffuser passage for
recovering static pressure by slowing down discharged air from an
outer circumferential end of an impeller that rotates within a
housing, wherein a hub side wall surface of said diffuser passage
is provided with an inclined area that approaches toward a shroud
side, in a position on a downstream side of a portion parallel with
a normal line direction of a section surface of an impeller exit.
Description
TECHNICAL FIELD
[0001] The present invention relates to a centrifugal compressor of
a turbo charger or the like.
BACKGROUND ART
[0002] Conventionally, a centrifugal compressor of a turbo charger
or the like to be used for an internal combustion engine of a motor
vehicle for example, is commonly known.
[0003] FIG. 5A is a sectional view showing a relevant section of a
conventional centrifugal compressor. A centrifugal compressor 10
shown in the drawing compresses fluid such as gas and air
introduced from outside a housing 11, by rotating an impeller 13
having a large number of blades 12 within the housing 11. The fluid
flow (airflow) formed in this way travels through an impeller exit
(Hereunder, also referred to as "diffuser entry") 14, being an
outer circumferential end of the impeller 13, then through a
diffuser passage 15 and a scroll 16, and is then delivered to the
outside. Reference symbol 17 in the drawing denotes a shaft axis
about which the impeller 13 rotates.
[0004] The diffuser passage 15 mentioned above is provided in
between the impeller exit 14 and the scroll 16, being a passage for
recovering static pressure by slowing down the airflow discharged
from the impeller 14. The diffuser passage 15 is normally formed
from a pair of opposing wall surfaces. In the description below,
one of the pair of the opposing wall surfaces is called a shroud
side wall surface 15a and the other is called a hub side wall
surface 15b.
[0005] In a turbo charger of a motor vehicle to be used in
combination with an internal combustion engine, since a wide
compressor operation range is required, a type of diffuser that
does not have vanes (vaneless diffuser) is normally employed.
[0006] Incidentally, in recent years, in response to an increase in
flow amount and pressure ratio of the centrifugal compressor 10,
distortion of the airflow flowing into the diffuser passage 15 is
becoming greater. It is thought that a flow with a large distortion
flowing into the diffuser passage 15 results in the occurrence of a
phenomenon known as surging, which determines the operation limit
on the small flow amount side in the diffuser passage 15.
[0007] In the mechanism that gives rise to surging it is thought
that surging occurs when a backflow area of the airflow reaches an
exit side end section of the diffuser passage 15. Moreover, since
the occurrence of the backflow area mentioned above is thought to
be caused by a flow on the compressor shroud side within the
diffuser passage 15, that is, distortion of the flow along the
shroud side wall surface 15a, a diffuser structure for reducing
such distortion in the flow is proposed.
[0008] The distortion in the flow mentioned above refers to the
flow velocity distribution or pressure distribution being in a
non-uniform state. Conventional techniques for making this uniform
employ a structure or method that changes a flow passage sectional
area of the diffuser passage 15, or that utilizes a circulation
passage or the like. Each of such conventional techniques has a
focus on reducing distortion that occurs on the entry side
(impeller exit 14 side) of the diffuser passage 15.
[0009] As a conventional technique for reducing the distortion
mentioned above, for example, provision of a convex section or a
concave section for changing the flow passage sectional area on the
wall surface of the diffuser passage 15 has been proposed. Such a
convex section or concave section regularize the airflow along the
circumferential direction by changing the passage shape in the
circumferential direction, thereby enabling an improvement in
compression efficiency. (for example, refer to Patent Document
1).
[0010] Patent Document 1: Japanese Unexamined Patent Application,
Publication No. Hei 10-176699
DISCLOSURE OF INVENTION
[0011] However, in a small centrifugal compressor such as a turbo
charger for a motor vehicle in particular, it is difficult to
measure the internal flow of the airflow flowing within the
diffuser passage. Therefore, since distortion in actual internal
flow has yet to be sufficiently understood and furthermore the
phenomena up to the point of surging have not been explained, it is
necessary to understand these and develop an effective surging
prevention method to widen the operation range of the centrifugal
compressor.
[0012] As shown in FIG. 5B, the conventional diffuser passage 15
generally has a shape in which a pair of opposing wall surfaces,
namely a shroud side wall surface 15a and a hub side wall surface
15b, are in a parallel form, so that an axial direction flow
passage width W of the diffuser passage 15 is constant in the
circumferential direction. Having examined a flow pattern of up to
surging, by carrying out internal flow measurement using a model
for the conventional diffuser passage 15 configured in this way, it
was revealed that in the downstream area of the backflow area
(shown with an arrow A in the drawing) becomes a flow area that
reaches the diffuser exit 18 side end section of the diffuser
passage 15, the airflow separates from the hub side wall surface
15b in the vicinity of the diffuser exit 18, forming a backflow
area (shown with an arrow B in the drawing). That is to say, it is
thought that it is not a shroud side backflow area A, but a
backflow area B which causes surging to occur.
[0013] It is thought that such a flow separation from the hub side
wall surface 15b occurring in the vicinity of the diffuser exit 18
cannot be suppressed by a conventional technique, as disclosed in
Patent Document 1 for example, in which airflow is regularized
along the circumferential direction by changing the passage shape
in the circumferential direction.
[0014] In consideration of the above circumstances, an object of
the present invention is to provide a centrifugal compressor having
a diffuser structure in which airflow is unlikely to separate from
a hub side wall surface on the hub side wall surface downstream
side within the diffuser passage (in the vicinity of the diffuser
exit).
[0015] The present invention employs the following means to solve
the above problems.
[0016] A centrifugal compressor according to the present invention
is a centrifugal compressor provided with a diffuser passage for
recovering static pressure by slowing down discharged air from an
outer circumferential end of an impeller that rotates within a
housing, wherein a hub side wall surface of the diffuser passage is
provided with an inclined area that approaches toward a shroud
side, in a position on a downstream side of a portion parallel with
a normal line direction of a section surface of an impeller
exit.
[0017] According to such a centrifugal compressor, since the hub
side wall surface of the diffuser passage is provided with the
inclined area that approaches the shroud side, in the position on
the downstream side of the portion parallel with the normal line
direction of the section surface of the impeller exit, the radial
direction velocity of the low velocity area that occurs on the hub
side wall surface increases in the inclined area, and the radial
direction velocity distribution within the diffuser passage is made
uniform.
[0018] The inclined area in this case is a portion of an inclined
plane, a curved surface, or a stepped plane, formed on the hub side
wall surface for example, and must be such that, in this inclined
area, the axial direction flow passage width of the diffuser
passage narrows down from the upstream side toward the downstream
side by inclining the hub side wall surface so as to approach
toward the opposed shroud side wall surface as it approaches the
downstream side.
[0019] In the above aspect of the invention, a preferable position
in the diffuser passage length direction for providing the inclined
area, in the diffuser passage in a range between the diffuser entry
taken as a base point (0) and the diffuser exit (1), is within a
range on the downstream side (exit side) having a ratio of 0.3 to
0.7.
[0020] Moreover, in the above aspect of the invention, it is
preferable that the inclined area provided in the diffuser passage
be such that the maximum value of an amount of projection from the
hub side wall surface toward the shroud side wall surface is set to
approximately 1/3 to 1/5 of the passage width, being equivalent to
the size of the measured backflow area.
[0021] Furthermore, in the above aspect of the invention, the
preferable inclination angle is less than or equal to 20 degrees
based on the normal line of the impeller exit section when the
inclined area is taken as a plane. However, a more preferable
inclination angle is between 2 degrees and 10 degrees, inclusive,
based on the normal line of the impeller exit section. An
excessively large inclination angle is not preferable, as the
airflow is re-accelerated due to the reduction in the passage area
in this case.
[0022] According to the present invention described above, since on
the hub side wall surface of the diffuser passage there is provided
the inclined area that approaches the shroud side in the position
on the downstream side of the portion parallel with the normal line
of the impeller exit section, the radial direction velocity of a
low velocity area that occurs on the hub side wall surface
increases in this inclined area. Therefore, the radial direction
velocity distribution within the diffuser passage is made uniform,
and separation of the airflow is unlikely to occur locally, so that
the surge flow rate can be reduced and the compressor operation
range can be widened.
[0023] Moreover, the present invention described above is suited
for widening the operation range of a small centrifugal compressor
provided with a vaneless diffuser, such as a turbo charger for a
motor vehicle, which requires a particularly wide compressor
operation range.
BRIEF DESCRIPTION OF DRAWINGS
[0024] [FIG. 1] is a sectional view of a diffuser passage showing a
first embodiment of a centrifugal compressor according to the
present invention.
[0025] [FIG. 2] is a sectional view showing a first modified
example of FIG. 1.
[0026] [FIG. 3] is a sectional view showing a second modified
example of FIG. 1.
[0027] [FIG. 4] is a sectional view of a diffuser passage showing a
second embodiment of a centrifugal compressor according to the
present invention.
[0028] [FIG. 5A] is a sectional view showing a relevant section of
the centrifugal compressor.
[0029] [FIG. 5B] is a sectional view showing a conventional
structure of a diffuser passage.
EXPLANATION OF REFERENCE SIGNS
[0030] 10: Centrifugal compressor [0031] 11: Housing [0032] 12:
Impeller [0033] 14: Impeller exit (diffuser entry) [0034] 15, 30:
Diffuser passage [0035] 15a, 30a: Shroud side wall surface [0036]
15b, 30b: Hub side wall surface [0037] 16: Scroll [0038] 18:
Diffuser exit [0039] 20: Inclined plane (inclined area) [0040] 21:
Inclined curved surface (inclined area) [0041] 22: Inclined
inflected line (inclined area) [0042] 33: Shroud side inclined
section (inclined area)
BEST MODE FOR CARRYING OUT THE INVENTION
[0043] Hereunder an embodiment of a centrifugal compressor
according to the present invention is described, based on the
drawings.
[0044] As shown in FIG. 5A, a centrifugal compressor 10 is provided
with a diffuser passage 15 that recovers static pressure by
reducing the velocity of a discharged air from an outer
circumferential end of an impeller 13 that rotates within a housing
11. The diffuser passage 15 is provided so as to connect between an
impeller exit (diffuser entry) 14 and a scroll 16, and is formed in
between a pair of opposing wall surfaces that comprise a shroud
side wall surface 15a and a hub side wall surface 15b.
[0045] FIG. 1 is a sectional view of the diffuser passage 15
showing a first embodiment. This diffuser passage 15 introduces
from the diffuser entry 14, the discharged air (indicated with
white arrows in the drawing) from the outer circumferential end of
the impeller 13, and allows the airflow guided to the passage
between the shroud side wall surface 15a and the hub side wall
surface 15b to flow out from a diffuser exit 18 into the scroll
16.
[0046] In the embodiment shown in the drawing, the hub side wall
surface 15b of the diffuser passage 15 is provided with an inclined
plane 20 that approaches the direction of the shroud side wall
surface 15a in a position on the downstream side in a portion
parallel with a normal line of the section of the impeller exit.
This inclined plane 20 is an inclined area, formed on the hub side
wall surface 15b of the diffuser passage 15, that becomes closer to
the shroud side wall surface 15a as the distance from the diffuser
entry 14 increases, approaching the diffuser exit 18 and narrowing
an axial direction flow passage width W, which is a distance
between the opposing wall surfaces, down to Wa.
[0047] That is to say, in the diffuser passage 15 of normal line
direction flow passage length L, the inclined area formed by the
inclined wall surface 20 inclines toward the direction of the
shroud side wall surface 15a from the upstream side of a passage of
a flow passage length La parallel with the normal line direction,
and is provided in a downstream portion of flow passage length Lb.
Here, taking 1 as the flow passage length L, the preferred length
of the downstream portion Lb, which becomes the inclined area, is a
portion remaining on the downstream side where the length La of the
upstream portion parallel with normal line direction is 0.3 to 0.7.
In other words, the preferred position for providing the inclined
area in the lengthwise direction of the diffuser passage 15 may be
set so that, where the flow passage length from the diffuser entry
14 which is taken as a base point (0), to the diffuser exit 18,
which is taken as an end point (1), is taken as L (L=1), the length
La of the upstream portion is set at a ratio of 0.3 to 0.7, and the
length Lb of the downstream portion is set at a ratio of 0.7 to
0.3. Therefore, since the flow passage length L is the total length
of the length La of the upstream portion and the length Lb of the
downstream portion (L=La+Lb), the total length L of the upstream
portion length La and the downstream portion length Lb is always
"1".
[0048] Moreover, it is preferable that the inclined area provided
in the diffuser passage 15 be such that a projection amount of the
inclined wall surface from the hub side wall surface 15b to the
shroud side wall surface 15a is set to be approximately 1/3 to 1/5
of the passage width at the diffuser exit 18, where the projection
amount of the inclined wall surface 20 reaches its maximum value
Wb. That is to say, since the maximum value Wb of the projection
amount is 1/3 to 1/5W (Wb.apprxeq.1/3 to 1/5W), the axial direction
flow passage width Wa narrowed by the inclined wall surface 20 is
set to be approximately 2/3 to 4/5 of the axial direction flow
passage width W (Wa.apprxeq.2/3 to 4/5W).
[0049] Moreover, as is the case with the inclined wall surface 20
mentioned above, the angle of inclination .theta. where the
inclined area is a plane surface, is preferably set less than or
equal to 20 degrees based on the normal line of the impeller exit
section. However, a further preferable angle of inclination .theta.
is greater than or equal to 2 degrees and less than or equal to 10
degrees based on the normal line of the impeller exit section.
[0050] The normal line and normal line direction of the impeller
exit section mentioned above refers to a straight line or direction
that extends radially outward from an axial center line 17 of
rotation of the impeller 13 and passes the impeller exit section,
and it practically approximates the airflow direction.
[0051] As described above, the diffuser passage 15 provided with
the inclined area formed by the inclined wall surface 20 is
provided with: an upstream side area where the shroud side wall
surface 15a and the hub side wall surface 15b are both parallel
with the normal line direction and the axial direction flow passage
width W is constant; and an inclined area on the downstream side
where the axial direction flow passage width W to the diffuser exit
18 side is narrowed by the inclined wall surface 20, in which the
hub side wall surface 15b inclines toward the shroud side wall
surface 15a.
[0052] Therefore the airflow introduced from the diffuser entry 14
is slowed down by flowing through the diffuser passage 15, and
recovers its static pressure. However, at this time, on the
downstream side closer to the diffuser exit 18, the airflow in a
low velocity area, which occurs in the vicinity of the wall surface
and is thought to cause the airflow to separate from the hub side
wall surface 15b, is guided to the inclined wall surface 20 so that
it gradually flows toward the shroud side wall surface 15a.
[0053] The low velocity area in this case is an area where a
velocity component in the radial direction from the diffuser entry
14 toward the diffuser exit 18 is low. In the example shown in the
drawing, the radial direction corresponds to the normal line
direction.
[0054] As a result, the airflow in the low velocity area that has
occurred in the vicinity of the wall surface of the hub side wall
surface 15b increases its velocity component in the radial
direction. Therefore, in the diffuser passage 15, the velocity
distribution in the radial direction becomes uniform and flow
separation is unlikely to occur locally.
[0055] As described above, if flow separation is unlikely to occur
locally in the diffuser passage 15, the surge flow rate can be
reduced, enabling the operation range of the centrifugal compressor
to be widened. In particular, if the invention is applied in the
case where a wide range of compressor operation is required from a
small sized centrifugal compressor such as a turbo charger provided
with a vaneless diffuser, widening of the range can be easily
achieved.
[0056] Incidentally, considering the case of providing a similar
inclined area on the shroud side wall surface 15a, the axial
direction flow passage width W becomes narrower in the opposite
direction as it approaches the diffuser exit 18. However, since
there is not a low velocity area which is thought to be a cause of
flow separation, present in close proximity to the wall surface of
the shroud side wall surface 15a in the vicinity of the diffuser
exit 18, the airflow guided to the inclined wall surface 20 is
accelerated by gradually flowing toward the hub side wall surface
15b. Therefore, a difference between the accelerated velocity on
the shroud side wall surface 15 and the velocity on the hub side
wall surface 15b, in which the low velocity area is present,
increases, and hence non-uniformity of the velocity distribution in
the radial direction increases.
[0057] Next, a first modified example of the inclined area
mentioned above is described, based on FIG. 2. The same reference
symbols are given to parts that are the same as in the above
embodiment, and detailed descriptions thereof are omitted.
[0058] In this first modified example, in place of the inclined
plane 20 in FIG. 1, an inclined curved surface 21 forms an inclined
area. This inclined curved surface 21 is the same as the inclined
plane 20 with respect to the preferred position along the diffuser
passage length direction in which the inclined area is to be
provided (ratio of length Lb), and with respect to the maximum
value Wb of the projection amount from the hub side wall surface
15b toward the shroud side wall surface 15a, and the curvature may
be appropriately set to satisfy these conditions. The curved
surface in this case may be either a concave curved surface or
convex curved surface when seen from inside the diffuser passage
15.
[0059] Since the radial direction velocity component of the low
velocity area airflow that has occurred in the vicinity of the wall
surface of the hub side wall surface 15b also increases even when
the inclined curved surface 21 provided is formed by such an
inclined area, the velocity distribution in the radial direction is
made uniform so that flow separation becomes unlikely to occur
locally.
[0060] Therefore, the surge flow rate can be reduced, and hence the
operation range of the centrifugal compressor can be widened and,
in particular, if the invention is applied in a case where a wide
range of compressor operation is required of a small size
centrifugal compressor provided with a vaneless diffuser, the
compressor operation range can be easily widened.
[0061] Next, a second modified example of the inclined area
mentioned above is described, based on FIG. 3. The same reference
symbols are given to parts that are the same as in the above
embodiment, and detailed descriptions thereof are omitted.
[0062] In this second modified example, in place of the inclined
plane 20 in FIG. 1, an inclined inflected line 22 forms an inclined
area. This inclined inflected line 22 is formed from a plane
inclined section 22a and a parallel section 22b on the diffuser
exit 18 side, the parallel section 22b in this case being parallel
to the shroud side wall surface 15a and the hub side wall surface
15b.
[0063] Moreover, this inclined inflected line 22 is the same as the
inclined plane 20 with respect to the preferred position along the
diffuser passage length direction in which the inclined area is to
be provided (ratio of length Lb), and with respect to the maximum
value Wb of the projection amount from the hub side wall surface
15b toward the shroud side wall surface 15a.
[0064] Since the radial direction velocity component of the low
velocity area airflow that has occurred in the vicinity of the wall
surface of the hub side wall surface 15b also increases even when
the inclined inflected line 22 provided is formed by such an
inclined area, the velocity distribution in the radial direction is
made uniform so that flow separation becomes unlikely to occur
locally.
[0065] Therefore, the surge flow rate can be reduced, and hence the
operation range of the centrifugal compressor can be widened and,
in particular, if the invention is applied in a case where a wide
range of compressor operation is required of a small size
centrifugal compressor provided with a vaneless diffuser, the
compressor operation range can be easily widened.
[0066] The inclined inflected line 22 shown in the drawing is a
combination of the inclined section 22a and the parallel section
22b. However, an inclined section 22a of two or more steps may be
combined, and furthermore, a curved surface may also be
combined.
[0067] FIG. 4 is a sectional view showing a second embodiment of
the centrifugal compressor according to the present invention. The
same reference symbols are given to parts that are the same as in
the first embodiment, and detailed descriptions thereof are
omitted.
[0068] In the present embodiment, a diffuser passage 30 is divided
into three areas. Specifically, from the upstream side, a hub side
inclined section 31, a parallel section 32 parallel with the normal
line direction of the impeller exit section, and a shroud side
inclined section 33 are integrally connected. Therefore, compared
to the first embodiment shown in FIG. 1, the hub side inclined
section 31 is added on the most upstream side, and, in the shroud
side inclined section 33, the shroud side wall surface 30a and the
hub side wall surface 30b are arranged parallel with each other so
as to incline toward the shroud side at the same inclination
angle.
[0069] When employing this kind of configuration also, in the
shroud side inclined section 33 of the diffuser passage 30, the hub
side wall surface 30b is provided with an inclined area that
approaches the shroud side in a position on the downstream side of
the parallel section 32, which is a portion parallel with the
normal line of the impeller exit section. That is to say, by having
the hub side wall surface 30b of the shroud side inclined section
33 approach the shroud side, an inclined area having the same
effect as that of the inclined plane 20 mentioned above is
formed.
[0070] As a result, since radial direction velocity component of
the low velocity area airflow that has occurred in the vicinity of
the wall surface of the hub side wall surface 30b is increased by
the hub side wall surface 30b that serves as an inclined plane
similar to the inclined plane 20, the velocity distribution in the
radial direction is made uniform so that flow separation becomes
unlikely to occur locally in the diffuser passage 30.
[0071] Therefore, the surge flow rate can be reduced, and hence the
operation range of the centrifugal compressor can be widened and,
in particular, if the invention is applied in a case where a wide
range of compressor operation is required of a small size
centrifugal compressor provided with a vaneless diffuser, the
compressor operation range can be easily widened.
[0072] As described above, on the hub side wall surface 15a of the
diffuser passage 15, since the inclined area that approaches the
shroud side is provided in a position on the downstream side of the
portion parallel with the normal line direction of the impeller
exit section, the radial direction velocity of the low velocity
area that occurs on the hub side wall surface 15a increases, and
the radial direction velocity distribution within the diffuser
passage 15 is made uniform. Therefore, airflow is unlikely to
separate locally from the wall surface in the vicinity of the
diffuser exit 18 of the diffuser passage 15, and hence the surge
flow rate can be reduced and the compressor operation range can be
widened.
[0073] The present invention is not limited to the above
embodiments and can be appropriately modified without departing
from the scope of the present invention.
* * * * *