1
DESCRIPTION
VARIABLE DIFFUSER AND COMPRESSOR
Technical Field
[0001]
The present invention relates to a variable diffuser
applied to, for example, centrifugal compressors and mixed
flow compressors, and a compressor furnished with this
variable diffuser.
Background Art
[0002]
Heretofore, centrifugal compressors, such as
turbochargers utilized in internal combustion engines for
automobiles, are known.
FIG. 17 is a cross-sectional view showing the main parts
of a conventional centrifugal compressor. The centrifugal
compressor 10 shown in the drawing compresses fluids, such as
gas and air introduced from the exterior of a housing 11, by
means of the rotation of an impeller 13, which is provided
with a plurality of vanes 12, within the housing 1.1. The flow
of the fluid (air flow), which is formed in this manner, is
delivered to the exterior through an impeller exit (hereunder
also referred to as the "diffuser entrance") 14 that becomes

2
the outer peripheral end of the impeller 13, a diffuser 15,
and a scroll (omitted from the drawing). Reference symbol 16
in the figure is a shaft axis about which the impeller 13
rotates.
[0003]
The diffuser 15 mentioned above is an air flow passage
provided between the impeller exit 14 and the scroll, and has
a function of restoring static pressure from dynamic pressure
by decelerating the air flow that is discharged from the
impeller exit 14. This diffuser 15 is normally formed by a
pair of opposing walls, and in the explanation below, one wall
amongst the opposing pair is referred to as a shroud side wall
17, and the other is referred to as a hub side wall 18.
Furthermore, examples of the diffuser 15 mentioned above
include a vaned diffuser furnished with a diffuser vane
(hereunder referred to as a "vane") 19 such as is shown in
FIG. 18, and a vaneless diffuser that does not have a vane 19.
[0004]
A common centrifugal compressor that is furnished with a
vaned diffuser employs a fixed vane diffuser in which the vane
19 is immovable. However, in a case where a flow rate range
enlargement of the centrifugal compressor is necessary, a
variable diffuser, in which the vane leading edge angle. (3k
shown in FIG. 20 (hereunder referred to as "vane angle (3k")
can be varied by making the vane 19 movable, is employed.

3
A general construction of the variable diffuser is, for
example, as shown in FIG. 18, one that varies the vane angle
βk by providing a pivot shaft 20 to the vane 19, and
supporting the vane 19 on the shroud side wall 17 and the hub
side wall 18, as well as rotating the vane 19 about this pivot
shaft 20.
[0005]
In regard to such a variable diffuser, a drive unit in
which the angle of a plurality of diffuser vanes is variable
by a simple construction has been proposed. This drive unit
is furnished with a large gear that rotates by means of an
actuator, and the like, and a plurality of gears that engage
the large gear, and the angle is varied by turning the
diffuser vanes that are connected to the gears. (For example,
refer to Patent Document 1)
Furthermore, in regard to a centrifugal compressor that
is furnished with a vaned diffuser, provision of a second
stationary vane that is freely rotatable with an object of
expanding the operation on the small flow rate side has been
proposed. (For example, refer to Patent Documents 2 and 3)
Patent Document 1: Japanese Unexamined Patent
Application, Publication No. Hei 7-310697
Patent Document 2: Publication of Japanese Patent No.
2865834
Patent Document 3: Publication of Japanese Patent No.

4
3513729
Disclosure of Invention
[0006]
Incidentally, in regard to the vane 19 of the variable
diffuser, in a case where the vane shape of the vane is
designed, it is set as a shape such that it becomes in the
middle of a desired flow rate variation range. Accordingly,
in conventional variable diffusers in which the vane 19 is
turned about the pivot shaft 20 and the vane angle βk is
variable, variations in the characteristics occur as shown in
FIG. 19. That is to say, the flow rate range, which is
prescribed by the surge flow rate Qs and the choke flow rate
Qc, for example as shown in FIG. 20, becomes wider by the
amount of the fluctuations of each corresponding surge flow
rate Qs and choke flow rate Qc as a result of turning the vane
19 within the range of a turning range 6 from the maximum vane
angle βmax to the minimum vane angle pmin.
[0007]
However, in a case where the flow rate range (the range
between which flow rate variations are possible) mentioned
above is widely set, as shown in FIG. 21, the flow angle β and
the vane angle βk of the vane 19 take variations of
respectively different inclinations. Consequently, since the
incidence (In) in the small flow rate region and the large

5
flow rate region becomes large, there is a problem in that the
efficiency decreases due to an increase in losses. The
incidence is a value that is defined by the difference between
the vane leading edge angle βk and the flow angle β.
Furthermore, in regard to the turning type variable
diffuser construction, a space 5 (refer to FIG. 18) is
provided between both side ends of the vane 19 and the shroud
side wall 17 and the hub side wall 18 in order to make smooth
turning of the vane 19 possible. Consequently, leaks occur in
the air flow that flows through the space 5, and a problem in
that the efficiency decreases over all flow rate ranges has
been pointed out.
[0008]
In this manner, since conventional variable diffusers
have a problem in the efficiency decreasing due to increases
in the incidence and leaks from the space 5, it is desired for
these problems to be solved and to further improve the
efficiency.
The present invention has been achieved taking the above
circumstances into account, with an object thereof in
providing a variable diffuser in which the efficiency can be
further improved, and a compressor furnished with this
variable diffuser.
[0009]
The present invention employed the following means in

6
order to solve the problems mentioned above.
The variable diffuser according to the present invention
is one which in a variable diffuser in which a diffuser
passage, which restores a static pressure from a dynamic
pressure by decelerating an air flow that is discharged from
an outer peripheral end of an impeller that rotates within a
housing, is formed between a hub side wall and a shroud side
wall, and diffuser vanes are provided in the diffuser passage,
is characterized in that said diffuser vanes are alternately
fixed in the circumferential direction to a wall member that
forms the hub side wall and the shroud side wall, and there is
provided a driving device that turns either one of the wall
members about the same axis as the rotation of the impeller.
[0010]
According to such a variable diffuser, since the diffuser
vanes are alternately fixed in the circumferential direction
to the wall member that forms the hub side wall and the shroud
side wall, and there is provided the driving device that turns
either one of the wall members about the same axis as the
rotation of the impeller, then by turning the wall member of
the movable side, the throat area can be varied without
changing the vane leading edge angle. Furthermore, the space
5 formed between the diffuser vane and the hub side wall and
the shroud side wall decreases since it becomes either one of
the faces.

7
In this case, it is preferable for a movable range of the
wall member which turns as a result of the driving device, to
be set such that it encompasses the entire width of an
interval between adjacent diffuser vanes that are fixed on the
wall member of the fixed side.
[0011]
In the above aspect of the invention, it is preferable
for a leading edge radius (R1) of a diffuser vane provided on
a turning side of the wall member to be set larger than a
leading edge radius (R2) of a diffuser vane provided on a
fixed side of the wall member (Rl > R2). As a result,
increases in the leading edge thickness of overlapping vanes
can be prevented.
[0012]
In the above aspect of the invention, it is preferable
for a vane leading edge angle (akl) of a diffuser vane
provided on a turning side of the wall member to be set
smaller than a leading edge angle (ak2) of a diffuser vane
provided on a fixed side of the wall member at the same radial
position (akl < ak2). As a result, the average vane leading
edge angle in a state where two vanes are overlapped can be
decreased.
[0013]
In the above aspect of the invention, it is preferable
for a vane leading edge angle (akl) of a diffuser vane

8
provided on a turning side of the wall member to be set larger
than a leading edge angle (αk2) of a diffuser vane provided on
a fixed side of the wall member at the same radial position
(αkl > αk2). As a result, the average vane leading edge angle
in a state where two vanes are overlapped can be increased.
[0014]
In the above aspect of the invention, it is preferable
for a diffuser vane provided on a fixed side of the wall
member to be a low chord-pitch ratio vane. As a result, the
characteristics at the time of a small flow rate can be
improved while retaining the characteristics of the low chord-
pitch ratio.
In this case, it is preferable for a trailing edge radius
(R3) of a diffuser vane provided on a turning side of the wall
member to be set larger than a trailing edge radius (R4) of a
diffuser vane provided on a fixed side of the wall member (R3
> R4). As a result, wide ranging of the flow rate range, and
the high pressure ratio can be simultaneously achieved.
[0015]
In the above aspect of the invention, the setting of the
fixed side and the turning side may be reversed.
That is to say, the entrance radius (R2) of the diffuser
vane provided on the fixed side of the wall member may be set
larger than the entrance radius (Rl) of the diffuser vane
provided on the turning side of the wall member (R2 > Rl).

9
Furthermore, the vane leading edge angle (αk2) of the
diffuser vane provided on the fixed side of the wall member
may be set smaller than the leading edge angle (αkl) of the
diffuser vane provided on the turning side of the wall member
at the same radial position (αk2 < αkl).
Furthermore, the diffuser vane provided on the turning
side of the wall member may be made a low chord-pitch ratio
vane.
Furthermore, the trailing edge radius (R4) of the
diffuser vane provided on the fixed side of the wall member
may be set larger than the trailing edge radius (R3) of the
diffuser vane provided on the turning side of the wall member
(R4 > R3) .
[0016]
In the above aspect of the invention, it is preferable
for the driving device to be furnished with a sliding
mechanism section that moves a turning side of the wall member
back and forth between a space formation position and a space
reduction position with respect to a fixed side of the wall
member. As a result, the space 5 can be minimized and the
efficiency can be improved.
[0017]
The compressor according to the present invention
comprises a variable diffuser according to any of -claim 1 to
claim 9 on the peripheral end of the impeller that rotates

10
within the housing.
[0018]
According to such a compressor, increases in the
incidence, and efficiency decreases resulting from leaks from
the space 5 are resolved, and it becomes a compressor
furnished with a variable diffuser that can further improve
efficiency.
[0019]
According to the present invention mentioned above, since
the throat area can be varied without changing the leading
edge angle of the movable side, efficiency decreases resulting
from increases in the incidence can be resolved, and
accordingly, a variable diffuser with further improved
efficiency and a compressor furnished with this variable
diffuser can be provided.
Furthermore, since the space 5 formed between the
diffuser vane and the hub side wall and the shroud side wall
becomes only one of the faces and decreases, it becomes
possible to resolve efficiency decreases resulting from leaks
from the space 5.
Brief Description of Drawings
[0020]
FIG. 1 is a drawing showing a first embodiment according
to a variable diffuser of the present invention, in which (a)

11
is an enlarged perspective view of the main parts, and (b) is
a cross-sectional view along A-A in (a).
FIG. 2 is a drawing showing the movement of the variable
diffuser shown in FIG. 1, in which (a) shows a case where All
= A12 is set, (b) shows a state in which a movable vane is in
contact with the pressure face of a fixed vane, and (c) shows
a case where it is set in the middle of (a) and (b).
FIG. 3 is a drawing showing the movement of a variable
diffuser according to a second embodiment of the present
invention, in which (a) shows a case where the movable vane
leading edge radius has been made large compared to the fixed
vane, (b) shows a case where the leading edge of the movable
vane is turned upstream of the intersection point X, and (c)
shows a case where the leading edge of the movable vane is
turned downstream of the intersection point X.
FIG. 4 is a drawing showing a variable diffuser according
to a third embodiment of the present invention.
FIG. 5 is a drawing showing the characteristics of the
variable diffuser shown in FIG. 4.
FIG. 6 is a drawing showing a variable diffuser according
to a fourth embodiment of the present invention.
FIG. 7 is a drawing showing the characteristics of the
variable diffuser shown in FIG. 6.
FIG. 8 is a drawing showing a variable diffuser according
to a fifth embodiment of the present invention.

12
FIG. 9 is a drawing showing a modified example of the
variable diffuser according to the fifth embodiment shown in
FIG. 8.
FIG. 10 is a drawing showing the relationship between the
pressure recovery factor and the number of vanes in regard to
a vaned diffuser and a low chord-pitch ratio diffuser.
FIG. 11 is a perspective view of the main parts showing a
variable diffuser according to a sixth embodiment of the
present invention.
FIG. 12 is an explanatory drawing of the sliding
mechanism section shown in FIG. 11, in which (a) is a drawing
showing the movement of a sliding face with respect to a
guiding face, and (b) is a drawing showing a space 5, which
varies together with the turning of a movable circular plate.
FIG. 13 is a drawing showing the state of the movable
circular plate and the movable vanes, which move by means of
the sliding mechanism section shown in FIG. 11.
FIG. 14 is a cross-sectional view showing a configuration
example in which a sliding face is provided to a wall that
becomes the vane interval between the movable vanes and the
fixed vanes.
FIG. 15 is a drawing showing a first modified example of
the sliding mechanism section shown in FIG. 11.
FIG. 16 is a drawing showing a second modified example of
the sliding mechanism section shown in FIG. 11.

13
FIG. 17 is a cross-sectional view showing the main parts
of a conventional centrifugal compressor.
FIG. 18 is a perspective view showing the main parts of a
conventional example of a variable diffuser.
FIG. 19 is a drawing showing the characteristics of the
variable diffuser shown in FIG. 18.
FIG. 20 is an explanatory drawing showing the movement of
the variable diffuser shown in FIG. 19.
FIG. 21 is a drawing showing the relationship between
incidence (In), and flow angle (β) and vane angle (βk) .
Explanation of Reference Signs:
[0021]
30: Variable diffuser
31: Movable circular plate
31a: Shroud side wall
32: Fixed circular plate
32a: Hub side wall
33: Diffuser passage
34, 34A-E: Movable diffuser vane (movable vane)
35: Fixed diffuser vane (fixed vane)
40, 40A: Driving device
41: Gear driving section
42: Rack gear section
43: Pinion gear

14
45, 45A: Sliding mechanism section
46: Guide rail
47: Concave groove section
48: Guiding groove
48a: Guiding face
49: Convex section
49a: Sliding face
Best Mode for Carrying Out the Invention
[0022]
Hereunder, an embodiment of a variable diffuser and a
compressor according to the present invention is described
with reference to the drawings.

The variable diffuser 30 shown in FIG. 1, for example,
restores a static pressure from a dynamic pressure by
decelerating the air flow that is discharged from the
peripheral end of an impeller that rotates within the housing
of a centrifugal compressor, a mixed flow compressor, or the
like. In regard to this variable diffuser 30, as well as a
diffuser passage 33 being formed between the opposing shroud
side wall 31a and hub side wall 32a, movable diffuser vanes
(hereunder called the "movable vanes") 34 and fixed diffuser
vanes (hereunder called the "fixed vanes") 35 are provided
within the diffuser passage 33.
Here, the vanes are made movable by providing the movable

15
vanes 34 to the shroud side wall 31a, although they may be
made movable by providing the movable vanes 34 to the hub side
wall 32a.
[0023]
Specifically describing the configuration of the movable
diffuser 30, the movable vanes 34 are fixed on a movable
circular plate (wall member) that forms the shroud side wall
31a, and the fixed vanes 35 are fixed on a fixed circular
plate (wall member) 32 that forms the hub side wall 32a. The
movable vanes 34 and the fixed vanes 35 are made the same vane
shape, and with respect to the shroud side wall 31a and the
hub side wall 32a, a plurality (vane number N) of the same
respective number is positioned in the circumferential
direction at a predetermined pitch.
FIG. 1 (a) shows a state where the movable circular plate
31 and the fixed circular plate 32, which is an opposing pair,
have been separated. From this state, the movable circular
plate 31 and the fixed circular plate 32 slide in the
combination direction shown by the arrow in the. drawing and
are integrated, such that the movable vanes 34 of the shroud
side wall 31a and the fixed vanes 35 of the hub side wall 32a
become alternately positioned in a predetermined reference
position in the circumferential direction at the same pitch.
That is to say, in an assembled state in which the movable
circular plate 31 and the fixed circular plate 32 have been

16
integrated, the movable vanes 34 and the fixed vanes 35 are
alternately arranged in a reference position in the
circumferential direction at the same' pitch. The cross-
sectional view of FIG. 1 (b) shows the A-A cross-section of
FIG. 1 regarding a diffuser passage 33 that is formed by
integrating the movable circular plate 31 and the fixed
circular plate 32.
[0024]
A driving device 40 for turning the movable circular
plate 31 through a predetermined turning range 9 in the
turning direction of the same axis as the rotation of the
impeller (shown by the white arrows in the drawing), is
provided on the movable circular plate 31 side. This driving
device 40 is, for example, configured by a gear driving
section 41 that is provided on the upper end section of the
movable circular plate 31, and a sliding mechanism section 45
that is provided on the lower end section. The turning range
9 in this case is, compared to the pitch at which the movable
vanes 34 and the fixed vanes 3 5 are alternately arranged in
the circumferential direction in the predetermined reference
position mentioned above, essentially approximately doubled
although a difference corresponding to the thickness of the
vanes is generated. In other words, the movable range 9
becomes the entire width between adjacent fixed vanes 35.
[0025]

17
The gear driving section 41 is a configuration in which a
rack gear section 42 and a pinion gear 43 formed on the upper
end face of the movable circular plate 31 are intermeshed.
The pinion gear 43 is connected to a drive source such as an
electric motor (not shown in the drawing), and is turnable as
necessary in the desired direction.
The sliding mechanism section 45 is a portion in which
the movable circular plate 31 is connected with respect to the
housing 11 such that it is slidable in the circumferential
direction. In the example shown in the drawing, a convex-
shaped guide rail 4 6 formed on the housing 11 and a concave
groove section 47 formed on the lower end face of the movable
circular plate 31 are engaged, and the movable circular plate
31 is configured such that it slides along the guide rail 46.
In regard to such a sliding mechanism section 45, a leakage
stopping measure (not shown in the drawing) is provided
between the guide rail 46 and the concave groove section 47 in
order to prevent leaking of the high pressure air flow, in
which a static pressure has been restored at the exit of the
diffuser passage 33, from the back face of the movable
circular plate 31 to the entrance side of the diffuser passage
33.
[0026]
As a result, the movable circular plate 31 is guided by
the sliding mechanism section 45 and turned in the same axis

18
as the rotation axis of the impeller gear driving section 41
as a result of the turning of the pinion gear 43, and
therefore, it relatively moves with respect to an immobile
fixed circular plate 32. Then the movable vanes 34 which are
integral with the movable circular plate 31, are moved from
the reference position in both circumferential directions
within the range of the movable range 9. That is to say, the
movable vanes 34 rotate towards the fixed vanes 35 on both
adjacent sides by turning from the reference position where
they are arranged at the same pitch, and as shown by the
imaginary line in FIG. 1 (b), they become turnable within the
movable range 9 without changing the angle of the vanes, from
a position in which the pressure faces of the movable vanes 34
make contact with the negative pressure face of the adjacent
fixed vane 35, to a position in which the negative pressure
faces of the movable vanes 34 make contact such that they
overlap with the pressure face of the adjacent fixed vane 35.
[0027]
The movable range 9 of the movable vanes 34 is more
specifically described based on FIG. 2.
FIG. 2 (a) shows a case where the movable vanes 34 are in
the reference position. In this state, in regard to the
movable vanes 34 and the fixed vanes 35 which have the same
vane shape, the respective same number (N) are arranged in the
circumferential direction at the same pitch. In this state,

19
the throats All and A12 which are formed between the movable
vane 34 and the fixed vanes 35 that are adjacent on both
sides, become equal. Consequently, the throat area of the
variable diffuser 30 becomes a value in which the number N of
movable vanes 34 has been multiplied to the total value (All +
A12) of the throats formed on both sides of the movable vanes
34.
[0028]
FIG. 2 (b) shows a state where the movable vanes 34 are
making contact with the pressure face of the fixed vanes 35.
In this case, since the vanes are making contact with each
other at some point, as well as the throat A12 becoming
, approximately zero, the throat All becomes a maximum (Allmax).
Then, such a maximum throat becomes larger than the total
value of the throats at the reference position mentioned above
(Allmax > All + A12), and the area of the throats increases by
approximately 1.2 to 1.3 times. In the explanation below, the
state in which the throat area becomes a maximum is referred
to as the throat maximum position.
In a case where the movable vanes 34 have turned in the
opposite direction from the reference position, since there is
no change in that both vanes are making contact at some point,
it becomes the same result.
[0029].
FIG. 2 (c) shows a case where the movable vanes 34 are in

20
an intermediate position between FIG. 2 (a) and FIG. 2 (b).
The throat area in this case is an approximately intermediate
value between the reference position and the throat maximum
position. Accordingly, by turning the movable vanes 34 in a
range within the movable range o the throat area can be
appropriately varied in a range between approximately 1.2 to
1.3 times the reference value.
[0030]
In regard to the configuration of the variable diffuser
30 mentioned above, the number of diffuser vanes, which
consists of the number of movable vanes 34 and fixed vanes 35,
essentially changes such that it doubles from N vanes to 2N
vanes. That is to say, in a case where N movable vanes 34 are
installed to the movable circular plate 31, and N fixed vanes
35 are installed to the fixed circular plate 32, 2N diffuser
vanes are present in a state where the movable vanes 34 and
the fixed vanes 35 are mutually separated. However, in a
state where the adjacent movable vanes 34 and fixed vanes 35
are mutually making contact, the air flow essentially flows
between N diffuser vanes.
As a result, by varying the throat area, the flow rate of
the compressor characteristic is varied. That is to say,
since the throat area increases by approximately 1.2 to 1.3
times, it is possible to widen the flow rate range by varying
the choke flow rate Qc shown in FIG. 19 by 20 to 30%.

21
[0031]
Furthermore, since the fixed vanes 35 and also the vane
leading edge angle (vane angle) β of the movable vanes 34 are
normally fixed, compared to a conventional variable diffuser
in which the vane angle β varies as a result of the turning of
the vane 19, as shown by the two-dot chain line in FIG. 21,
the change in the incidence is very small. Accordingly, since
a compressor that is furnished with this variable diffuser 30
can reduce the increasing losses when the incidence becomes
large, the efficiency can be improved over conventional
technology.
Furthermore, since one end of the movable vanes 34 and
the fixed vanes 35 are fixed to a wall that forms the diffuser
passage 33, a space 5 is consequently formed only in one of
the vane width directions. Accordingly, compared to the
conventional structure in which the vane 19 is turned, since
the area of the space 5 can be reduced by half, the losses
resulting from leakage of the air flow are reduced by half,
and the efficiency can be improved.
[0032]

Next, a second embodiment of the present invention is
described based on FIG. 3.
In regard to the movable vanes 34A of this embodiment,
the entrance radius Rl is set larger than the entrance radius

22
R2 of the fixed vanes 35. That is to say, the entrance radius
Rl of the movable vanes 34A is, in a case where the movable
vanes 34A are in an intermediate position between the adjacent
fixed vanes 35, set such that the leading edges of the movable
vanes 34A are on the upstream side with respect to the throat
A2 formed between the adjacent fixed vanes 35. In the example
shown in the drawing, the throat area varies only within a
range in which the leading edges of the movable vanes 34A are
upstream with respect to the intersection point X between the
throat A2 and the radius Rl.
[0033]
Hereunder, this is specifically described based on the
drawings.
As shown in FIG. 3 (a), in a case where the movable vanes
34A are positioned approximately in the center of the fixed
vanes 35, the throat area becomes a minimum.
As shown in FIG. 3 (b) , in a case where the movable vanes
34A are positioned upstream of the throat A2, the total value
of the throat All and the throat A12 (All + A12) gradually
increases.
As shown in FIG. 3 (c), when the leading edge of the
movable vanes 34A is positioned downstream of the throat A2,
the throat area becomes a value in which the number of vanes N
has been multiplied to the throat A2, and the throat reaches a
maximum A2, and it does not increase even if the movable vanes

23
34A are rotated.
[0034]
Incidentally, in the state of FIG. 2 (b) mentioned above,
the vane ends of the movable vanes 34 and the fixed vanes 35
mutually overlap with a limited space, and it becomes a state
where the vane thickness of the diffuser vane leading edges
has become thick. Such an increase in the vane thickness not
only becomes a problem that increases the throat area to the
maximum, but it also increases damage to the vane leading
edges.
However, in the state shown in FIG. 3 (c) , the leading
edges of the movable vanes 34A are positioned downstream of
the leading edges of the fixed vanes 35. Accordingly,
compared to the state shown in FIG. 2 (b), the sizes of the
throat becomes A2 > Allmax. In this manner, if the entrance
radius Rl is set larger than the entrance radius R2 (Rl > R2),
in regard to the movable range of the throat area, the maximum
value becomes larger.
Furthermore, in the state shown in FIG. 3 (c) , the vane
leading edges are essentially reduced by half to the number of
fixed vanes 35, and damage to the vane leading edges
decreases.
[0035]

Next, a third embodiment of the present invention is

24
described based on FIG. 4 and FIG. 5.
In regard to the movable vanes 34B of the present
embodiment, in the same radial position, the vane leading edge
angle (vane angle) αkl is set smaller than the vane angle αk2
of the fixed vanes 35, and the movable vanes 34B are driven
from the middle between the fixed vanes 35 towards the
negative pressure faces of the fixed vanes 35.
If made such a configuration, although the maximum value
of the throat A12 becomes small compared to the throat A2, in
a state where two vanes have been made to overlap, the average
vane angle αk can be decreased.
[0036]
As a result, in regard to the characteristics of the
compressor, as shown in FIG. 5, the flow angle a at the
maximum angle becomes smaller, and from the comparison between
the solid line representation and the broken line
representation, it can be understood that the performance when
the flow rate is low has been improved. Furthermore, also at
an intermediate angle, from the comparison between the solid
line representation and the broken line representation, it can
be understood that the performance at the time of a small flow
rate when the flow angle a is small has been improved, though
not as much as at the time of a maximum angle.
That is to say, the setting of the vane angle ak such
that akl < αk2 places an importance on the performance at the

25
time of a small flow rate when the flow angle a is small, and
at the time of the maximum angle and the time of an
intermediate angle, a performance improvement that improves
the pressure ratio in the low flow rate regions can be
obtained.
[0037]

Next, a fourth embodiment of the present invention is
described based on FIG. 6 and FIG. 7.
In regard to the movable vanes 34C of this embodiment,
the vane leading edge angle (vane angle) αkl is set larger
than the vane angle αk2 of the fixed vanes 35 at the same
radial position, and the movable vanes 34C are driven from the
middle of the fixed vanes 35 towards the pressure face of the
fixed vanes 35.
If made such a configuration, in the same manner to the
second embodiment mentioned above, in regard to the throat, A2
becomes a maximum value. On the other hand, in regard to the
choke flow rate Qc, since the flow angle a of the diffuser
entrance flows approximately perpendicular to the throat A2,
it also becomes an even larger angle with respect to the
pressure face angle of the fixed vanes 35. Consequently, the
negative incidence becomes large, the losses are large, and it
essentially becomes a cause of the reduction of the choke flow
rate.

26
[0038]
However, in this embodiment, in a state where the movable
vanes 34C and the fixed vanes 35 are making contact, and two
vanes have come together, the average vane angle ak can be
increased.
As a result, in regard to the characteristics of the
compressor, as shown in FIG. 7, at the time of a large flow
rate at a maximum angle when the flow angle a is large, from
the comparison between the solid line representation and the
broken line representation, it can be understood that the
performance has improved as a result of a rise in the pressure
ratio. Furthermore, also at an intermediate angle, from the
comparison between the solid line representation and the
dotted line representation, it can be understood that the
performance at the time of a large flow rate when the flow
angle a is large has been improved, though not as much as at
the time of the maximum angle.
That is to say, the setting of the vane angle ak such
that αkl > αk2 places an importance on the performance at the
time of a large flow rate when the flow angle a is large, and
at the time of the maximum angle and at the time of an
intermediate angle, a performance improvement that improves
the pressure ratio in the large flow rate regions can be
obtained.
[0039]

27

Next, a fifth embodiment of the present invention is
described based on FIG. 8 to FIG. 10.
In regard to vaned diffusers, those in which the shortest
distance between adjacent vanes is not formed in the
perpendicular direction from the vane negative pressure face,
or in other words, those in which a throat is not formed, are
generally distinguished by being called a "low chord-pitch
ratio diffuser". This low chord-pitch ratio diffuser has the
following characteristics.
[0040]
In regard to a vaneless diffuser, since the surge flow
rate Qs is small and the choke flow rate Qc is large, it has a
characteristic in that although the flow rate range is wide,
the efficiency is low.
On the other hand, in regard to a vaned diffuser, since
the surge flow rate Qs is large, and the choke flow rate Qc is
only 10 to 20% larger than the surge flow rate Qs, it has a
characteristic in that although the flow rate range is narrow,
the efficiency is high.
In contrast, in regard to the low chord-pitch ratio
diffuser, since a throat is not formed, the choke flow rate Qc
becomes larger than in the vaned diffuser, and the surge flow
rate Qs becomes larger than in the vaned diffuser.
Accordingly, the low chord-pitch ratio diffuser has a

28
characteristic in that the efficiency becomes higher than the
vaneless diffuser. In regard to the low chord-pitch ratio
diffuser, the movable vanes, in which a throat is not formed,
are called "low chord-pitch ratio vanes".
[0041]
FIG. 10 shows, as the characteristics of the diffuser, in
regard to the vaned diffuser and the low chord-pitch ratio
diffuser, the relationship between the pressure restoration
factor and the number of vanes.
When the number of vanes is varied in a normal vaned
diffuser, as shown by the solid line in the drawing, when the
number of vanes becomes a small number of vanes from
approximately 10 vanes, the pressure restoration factor
quickly decreases, and the case of zero vanes as the limit
corresponds to a vaneless diffuser.
On the other hand, in the low chord-pitch ratio diffuser,
since vanes where the size of the vane itself is smaller than
in a normal vaned diffuser are used, then as shown with by the
chain line in the drawing, even if the number of vanes is made
large, the pressure restoration factor does not become high to
the level of the normal vaned diffuser.
[0042]
Therefore, in the fifth embodiment, in a low chord-pitch
ratio diffuser as shown in FIG. 8, provided with low chord-
pitch ratio vanes with a sufficiently small number of fixed

29
vanes 35 and in which a throat is not formed, an imaginary
throat A2 is formed, and the second embodiment mentioned above
is applied.
That is to say, in regard to the movable vanes 34D of
this embodiment, the entrance radius Rl is set larger than the
entrance radius R2 of the fixed vanes 35. Accordingly, in
regard to the entrance radius Rl of the movable vanes 34D, in
a case where the movable vanes 34D are in an intermediate
position between the adjacent fixed vanes 35, the vane leading
edge of the movable vane 34D is set such that it becomes on
the upstream side with respect to the imaginary throat A2
formed between adjacent fixed vanes 35.
[0043]
If made such a configuration, it exhibits the same
pressure restoration factor as N low chord-pitch ratio vanes
in a case where the movable vanes 34D and the fixed vanes 35
are overlapped, and in a case where both vanes are installed
with the same spacing, the pressure restoration factor becomes
high since the number of vanes becomes 2N. Accordingly, if
the configuration of the present embodiment is employed, the
performance can be improved, while retaining the
characteristics of the low chord-pitch ratio diffuser, by
setting the movable vanes 34D and the fixed vanes 35 at the
same spacing at the time of a small flow rate.
[0044]

30
Next, a modified example of the present embodiment is
shown in FIG. 9 and is described. In this modified example,
the fixed vanes 35 are low chord-pitch ratio vanes in the same
manner as the embodiment shown in FIG. 8, and furthermore, the
trailing edge radius R3 of the movable vanes 34E is set larger
than the trailing edge radius R4 of the fixed vanes 35.
If made such a configuration, the following
characteristics can be obtained. That is to say, as shown in
FIG. 9 (a), in a case where the movable vanes 34E and the
fixed vanes 35 are separated and the number of vanes becomes
2N, since the vane area of the movable vanes 34E becomes
larger than the low chord-pitch ratio diffuser, the pressure
restoration factor rises.
Furthermore, in a case where the movable vanes 34E are in
the position shown in FIG. 9 (b) , it exhibits wide-range
characteristics in which a throat is not formed.
Then, in a case where the movable vanes 34E are in the
position shown in FIG. 9 (c), a high pressure restoration
factor is exhibited in the same manner as the normal vaned
diffuser in which the number of vanes has been made N vanes.
[0045]
Consequently, when the movable vanes 34E are farther on
the pressure face side of the fixed vanes 35 than the actual
throat, since the fixed vanes 35 function as low chord-pitch
ratio vanes, while retaining the wide ranging in which the

31
flow rate range defined by the choke flow rate Qc and the
surge flow rate Qs is expanded, an effect in which the
pressure buildup is increased by the movable vanes 34E is
obtained. Accordingly, if the configuration of this
embodiment is employed, since the characteristics can be
improved, while retaining the characteristics of the low
chord-pitch ratio diffuser, by setting the movable vanes 34E
and the fixed vanes 35 at the same spacing at the time of a
small flow rate, wide ranging (expansion of the flow rate
range) and a high pressure ratio can be simultaneously
achieved.
[0046]

Next, a sixth embodiment of the present invention is
described based on FIG. 11 to FIG. 16.
This embodiment relates to the sliding mechanism section
45 of the driving device 40 that turns the movable circular
plate 31, and in particular, relates to a suitable structure
for reducing the space 5 between the wall of the fixed
circular plate 32 and the movable vanes 34.
A driving device 40A shown in FIG. 11 is furnished with a
sliding mechanism section 45A that is configured by a guiding
groove 48 that is formed on the housing 11, and a convex
section 49 that is provided on the lower end section of the
movable circular plate 31.

32
[0047]
On one side face of the guiding groove 48, a guiding face
48a, to which circular arc-shaped (radius R) concavities and
convexities are formed, is provided In the same manner, on the
convex section 49 side, with respect to the side face that
opposes the guiding face 48a, a sliding face 49a to which the
same circular arc-shaped (radius R) concavities and
convexities are formed, is provided. This sliding face 49a
makes contact with the guiding face 48a, and as a result of
the movable circular plate 31 turning, the circular arc-shaped
concave and convex contact positions that are formed on both
faces move in the circumferential direction.
Furthermore, on the housing 11 is installed a sealing
member 50 that exhibits a sealing function by making contact
with a face that becomes the outer circumferential side of the
movable circular plate 31 viewed from the diffuser passage 33
side. This sealing member 50 prevents the air flow which
flows through the diffuser passage 33, from passing through
the sliding mechanism section 45A and leaking.
[0048]
If made such a configuration, the movable circular plate
31 moves according to the concave and convex contact positions
with the guiding face 48a and the sliding face 49a, in a
direction that approaches or a direction that separates from
the fixed circular plate 32, and the interfacial distance with

33
the fixed circular plate 32 is varied. Hereunder, this
interfacial distance variation is specifically described with
reference to FIG. 12 and FIG. 13.
The movable circular plate 31, as a result of the movable
circular plate 31 side turning, moves back and forth in the
circular arc radius R direction between the space forming
position at which the convex section formed on the guiding
face 48a of the fixed side and the convex section formed on
the sliding face 49a make contact (indicated by the broken
line in FIG. 12 (a)), and the space reducing position at which
the concavities and convexities of the guiding face 48a and
the concavities and the convexities of the sliding face 49a
mutually engage (indicated by the solid line in FIG. 12 (a)).
[0049]
As a result, the space 5 formed between the end of the
movable vanes 34 and the hub side wall 32a is, as shown in
FIG. 13, varied within a range from a maximum value at the
space forming position (indicated by the chain in the drawing)
to a minimum value at the space reduction position (indicated
by the solid line in the drawing).
FIG. 12 (b) shows the change in the space 5 that
corresponds to the movable range 9 of the movable circular
plate 31. The minimum space at the space reduction position
can, by optimizing the concavities and convexities of the
guiding face 48a and the concavities and convexities of the

34
sliding face 49a, be made δ ≈ 0, which is equivalent to almost
none. Consequently, at the space reduction position, since
the leakage amount that passes through the space 5 decreases,
the efficiency of the compressor furnished with the variable
diffuser can be improved.
[0050]
Furthermore, it is preferable for the sliding mechanism
section 45A mentioned above to utilize the space reduction
position at which the concavities and convexities of the
guiding face 4 8a and the concavities and convexities of the
sliding face 49a engage, and for it to be turned in stages at
the pitch of the concavities and the convexities.
That is to say, since the position of the movable vanes
34 is fixed in stages, it becomes possible to prevent
fluctuations of the vane position resulting from play in the
driving device 40A and vibrations from the exterior, and the
characteristics of the compressor can be stabilized.
[0051]
Furthermore, in the variable diffuser mentioned above,
for example as shown in FIG. 14, a sliding face 51 is formed
on the shroud side wall 31a, which becomes the interval
between the movable vanes 34, and on the hub side wall 32a,
which becomes the interval between the fixed vanes, in order
to obtain satisfactory slidability even in a state where there
is no space δ. Specifically, it is acceptable if, on the

35
walls that become the interval between both vanes, for
example, the sliding face is formed by applying a fluororesin
such as 4-fluoroethylene.
If made such a configuration, smooth turning of the
movable circular plate 31 becomes possible even if there is no
space 5. Furthermore, by pressing from the back face side of
the movable circular plate 31 as a result of the diffuser exit
pressure, it is possible to achieve an improvement in
efficiency even if there are no concavities and convexities
such as on the guiding face 48a and the sliding face 49a as
mentioned above, and without a space 5.
[0052]
Incidentally, in the explanation above, the guiding face
48a and the sliding face 49a were made a circular arc shape,
although as in a first modified example shown in FIG. 15, it
is acceptable for it to be made a guiding face 48b and a
sliding face 49b having mutually identical sine wave-shaped
concavities and convexities.
Alternatively, as in a second modified example shown in
FIG. 16, it may be made a configuration in which a guiding
groove 48' is formed on the housing 11 which becomes the fixed
side, and freely turning rotation rings 52 are installed in a
necessary number at appropriate positions on this guiding
groove 48'. In this case, when the movable circular plate 31
turns, the circular arc-shaped or sine wave-shaped sliding

36
face 49a slides with respect to the rotation rings 52.
Therefore in the same manner as with the guiding faces 48a and
48b mentioned above, the space 5 can be eliminated at the
space reduction position.
[0053]
Furthermore, in regard to the setting of the movable
vanes and the fixed vanes described in the embodiments
mentioned above, the setting of the fixed side and the turning
side may be reversed. That is to say, the same respective
operating effects can be obtained even if the magnitude of the
entrance radius of the fixed vanes and the entrance radius of
the movable vanes are reversed, or the magnitude of the vane
leading edge angle of the fixed vanes and the vane leading
edge angle of the movable vanes is reversed, or the vanes of
the fixed vanes and the movable vanes that are made the low
chord-pitch ratio vanes are reversed, and furthermore, if the
magnitude of the trailing edge radius of the fixed vanes and
the trailing edge radius of the movable vanes are reversed.
[0054]
In this manner, according to the variable diffuser
structure of the present invention, efficiency decreases
resulting from increases in the incidence, and leakage from
the space 5 are resolved, and a variable diffuser, in which
the efficiency is even more improved, can be provided.
Accordingly, in regard to compressors such as centrifugal

37
compressors and mixed flow compressors, that are furnished
with this variable diffuser, the performance thereof can be
even more improved.
The present invention is in no way restricted to the
embodiments mentioned above, and appropriate changes are
possible within a range that does not depart from the gist of
the present invention.
Industrial Applicability
[0055]
The diffuser and the compressor of the present invention
is, for example, applicable to turbochargers, marine
superchargers, aeronautical small gas turbines, and industrial
centrifugal compressors and mixed flow compressors.

38
CLAIMS
1. A variable diffuser in which a diffuser passage, which
restores a static pressure from a dynamic pressure by
decelerating an air flow that is discharged from an outer
peripheral end of an impeller that rotates within a housing,
is formed between a hub side wall and a shroud side wall, and
diffuser vanes are provided in the diffuser passage,
said diffuser vanes being alternately fixed in the
circumferential direction to a wall member that forms said hub
side wall and said shroud side wall, and there being provided
a driving device that turns either one of said wall members
about the same axis as the rotation of said impeller.
2. A variable diffuser according to claim 1, wherein a
movable range of said wall member which turns as a result of
said driving device, is set such that it encompasses the
entire width of an interval between adjacent diffuser vanes
that are fixed on the wall member of the fixed side.
3. A variable diffuser according to either one of claim 1
and claim 2, wherein a leading edge radius (Rl) of a diffuser
vane provided on a turning side of said wall member is set
larger than a leading edge radius (R2) of a diffuser vane
provided on a fixed side of said wall member (Rl > R2).

39
4. A variable diffuser according to claim 3, wherein a vane
leading edge angle (αkl) of a diffuser vane provided on a
turning side of said wall member is set smaller than a leading
edge angle (αk2) of a diffuser vane provided on a fixed side
of said wall member at the same radial position (αkl < αk2).
5. A variable diffuser according to claim 3, wherein a vane
leading edge angle (αkl) of a diffuser vane provided on a
turning side of said wall member is set larger than a leading
edge angle (αk2) of a diffuser vane provided on a fixed side
of said wall member at the same radial position (αkl > αk2).
6. A variable diffuser according to claim 3, wherein a
diffuser vane provided on a fixed side of said wall member is
a low chord-pitch ratio vane.
7. A variable diffuser according to claim 6, wherein a
trailing edge radius (R3) of a diffuser vane provided on a
turning side of said wall member is set larger than a trailing
edge radius (R4) of a diffuser vane provided on a fixed side
of said wall member (R3 > R4).
8. A variable diffuser according to any one of claim 3
through and claim 7, wherein the setting of the fixed side and

40
the turning side is reversed.
9. A variable diffuser according to any one of claim 1
through and claim 7, wherein said driving device is furnished
with a sliding mechanism section that moves a turning side of
said wall member back and forth between a space formation
position and a space reduction position with respect to a
fixed side of said wall member.
10. A compressor comprising a variable diffuser according to
any one of claim 1 through claim 9 on the peripheral end of
the impeller that rotates within the housing.

There is provided a variable diffuser for a compressor in
which the efficiency can be further improved. In a variable
diffuser 30 in which a diffuser passage 33, which restores a
static pressure from a dynamic pressure by decelerating an air
flow that is discharged from an outer peripheral end of an
impeller that rotates within a housing, is formed between a
hub side wall 32a and a shroud side wall 31a, and diffuser
vanes are provided in the diffuser passage 33, fixed vanes 35
and movable vanes 34 that are the diffuser vanes, are
alternately fixed in the circumferential direction to a fixed
circular plate 32 and a movable circular plate 31 that form
the hub side wall 32a and the shroud side wall 31a, and there
is provided a driving device 40 that turns the movable
circular plate 31 about the same axis as the rotation of the
impeller.