U.S. patent number 3,782,850 [Application Number 05/169,997] was granted by the patent office on 1974-01-01 for energy transfer machine.
This patent grant is currently assigned to The Garrett Corporation. Invention is credited to Fredrick E. Burdette, Hans Egli, James H. Nancarrow.
United States Patent |
3,782,850 |
Egli , et al. |
January 1, 1974 |
ENERGY TRANSFER MACHINE
Abstract
An energy transfer machine is disclosed including a casing
enclosing a stator ring, the casing and ring conjointly defining a
smooth wall, annular fluid passage extending about the axis of
rotation between inlet and outlet passages formed in the casing. A
rotor within the casing includes a blade cascade projecting in
cantilever fashion into the annular fluid passage, each blade
having leading and trailing edges extending generally parallel with
the axis of rotation of the machine, the edge nearer the axis of
rotation being longer than the edge further from the axis. The
geometries and relative positions of the blades and annular fluid
passage are such that the radial distance from the axis of rotation
of the centroid of the meridional cross-section of the annular
fluid passage is larger than the radial distance of at least the
major portion of the edge nearer the rotational axis and smaller
than the radial distance from the axis of rotation of at least the
major portion of the edge further from the rotational axis.
Machines according to the invention are also characterized by
constructional features which minimize the number of castings
required and thereby greatly simplify the fabrication and structure
to minimize cost.
Inventors: |
Egli; Hans (Santa Monica,
CA), Burdette; Fredrick E. (Torrance, CA), Nancarrow;
James H. (Torrance, CA) |
Assignee: |
The Garrett Corporation (Los
Angeles, CA)
|
Family
ID: |
22618093 |
Appl.
No.: |
05/169,997 |
Filed: |
August 9, 1971 |
Current U.S.
Class: |
415/55.3;
415/55.4; 415/83 |
Current CPC
Class: |
F16H
41/26 (20130101) |
Current International
Class: |
F16H
41/00 (20060101); F16H 41/26 (20060101); F04d
005/00 () |
Field of
Search: |
;415/52,53,53T,83,56,57,58 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Husar; C. J.
Attorney, Agent or Firm: Robert H. Fraser et al.
Claims
What is claimed is:
1. A machine for transferring energy between a fluid medium and a
shaft rotatable about an axis, comprising:
a casing having inlet and outlet openings and enclosing a stator
ring and defining therewith a vaneless fluid passage extending
circumferentially about said axis; and
a rotor mounted on said shaft and having blades projecting into
said fluid passage, said blades having inner and outer edges
relative to said axis, the radial distance from said axis to the
centroid of the meridional cross-section of said fluid passage
lying between the radial distances from said axis to at least major
portions of said inner and outer edges.
2. A machine, as defined in claim 1, in which said inner edges are
longer than said outer edges.
3. A machine, as defined in claim 1, in which at least one of said
inner and outer edges extends parallel with said axis.
4. A machine, as defined in claim 1, in which the casing includes
inlet and outlet passages communicating with said fluid passage
through said inlet and outlet openings, said inlet passage being
oriented to direct the fluid so that the absolute velocity thereof
approaches the blade cascade approximately perpendicular to the
direction of movement of said cascade, said outlet passage being
oriented in approximate alignment with the direction of the
absolute velocity of the exiting fluid approaching said outlet
passage.
5. A machine, as defined in claim 1, in which the fluid moves away
from said axis of rotation during its passage through the blade
cascade.
6. A machine as defined in claim 1, in which the fluid moves toward
said axis of rotation during its passage through the blade
cascade.
7. A machine for transferring energy between a fluid medium and a
rotatable shaft, comprising:
a casing having a smooth interior wall surface defining a
smooth-walled toroidal space about a central axis of rotation, said
casing including fluid inlet and outlet openings;
a block seal within said toroidal space separating said inlet and
outlet openings;
a stator ring mounted within said toroidal space and defining with
said casing an annular fluid passage extending circumferentially
about said axis of rotation, the meridional cross-section of said
annular fluid passage having a centroid; and
a rotor mounted on said shaft for rotation about said axis and
including along its outer periphery a blade cascade, each blade
having an inner edge and an outer edge, said inner edge being
positioned closer to said axis than said outer edge, at least a
major part of said inner edge lying radially inward of said
centroid and at least a major part of said outer edge lying
radially outward of said centroid.
8. A machine, as defined in claim 1, in which the projection of
each blade on a meridional plane has a generally trapezoidal
configuration and includes a tip, said stator ring including a
surface immediately adjacent said blade tips and having a
configuration corresponding to said tips.
9. A machine, as defined in claim 7, in which said inlet and outlet
openings are in close angular proximity to one another and said
block seal has side surfaces generally coinciding with meridional
planes.
10. A machine, as defined in claim 7, in which said casing includes
inlet and outlet passages and said block seal has a portion fairing
smoothly into said outlet passage.
11. A machine, as defined in claim 7, in which the meridional
cross-section of said annular fluid passage varies between said
inlet and outlet openings to compensate for compressibility of the
fluid.
12. In a machine for transferring energy between a fluid medium and
a shaft rotatable about an axis, said machine including a casing
and stator ring enclosed within said casing, said casing and ring
defining an annular fluid passage extending about said axis, inlet
and outlet passages in said casing in communication with said fluid
passage, a rotor mounted on said shaft and carrying a blade cascade
extending into said fluid passage in close proximity to said stator
ring, each blade of said cascade having leading and trailing edges,
one of which edges is closer to the axis than the other, the
improvement in which the edge closer to said axis is longer than
the other edge.
13. A machine, as defined in claim 12, in which the centroid of the
meridional cross-section of said annular passage lies at a radial
distance from said axis that is between the radial distances from
said axis to at least major portions of said leading and trailing
edges.
14. A machine, as defined in claim 12, in which said edges extend
generally parallel with said axis of rotation.
15. A machine for transferring energy between a fluid medium and a
shaft rotatable about an axis, comprising:
a casing having inlet and outlet openings and enclosing a stator
ring and defining therewith a fluid passage extending
circumferentially about said axis; and
a rotor mounted on said shaft and having blades projecting into
said fluid passage, said blades having leading and trailing edges
generally parallel with said axis, one of said edges lying closer
to said axis than the other of said edges, the edge closer to said
axis being longer than said other edge.
16. A machine for transferring energy between a fluid medium and a
shaft rotatable about an axis, comprising:
a casing having inlet and outlet openings and enclosing a stator
ring and defining therewith a fluid passage extending
circumferentially about said axis; and
a rotor mounted on said shaft and having blades projecting into
said fluid passage, said blades having leading and trailing edges
generally parallel with said axis and in which the radial distance
from said axis to the centroid of the meridional cross-section of
the fluid passage lies between the radial distances to said leading
and trailing edges.
17. A machine for transferring energy between a fluid medium and a
shaft rotatable about an axis, comprising:
a casing enclosing a stator ring and defining therewith a fluid
passage extending circumferentially about said axis, said casing
including an inlet passage and an outlet passage, said passages
communicating with said fluid passage through inlet and outlet
openings; and
a rotor mounted on said shaft and including a blade cascade
projecting into said fluid passage and separated from said stator
ring by a close running clearance, the blades of said cascade
having leading edges and trailing edges, said inlet passage being
oriented to direct the fluid generally radially to enter the blade
cascade approximately perpendicular to the direction of movement of
said cascade past said inlet opening, said outlet passage being
oriented in approximate alignment with the direction of the
absolute velocity vectors of the fluid exiting from said blade
cascade.
18. A machine, as defined in claim 17, in which said inlet and
outlet openings are in close circumferential approximation and
separated by a block seal having a notch conforming to the contour
of said outlet passage.
19. A machine, as defined in claim 18, in which said block seal has
side surfaces generally coinciding with meridional planes.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to turbomachines and more
particularly to turbomachines in which the fluid is constrained to
pass at least twice through the blades of a single rotor.
2. Description of the Prior Art
The prior art includes reentry machines utilizing a single rotor to
gain multi-stage performance. These machines are designed to
deliver a high specific work output, that is, a high work output
per unit weight of working fluid. After there has been a partial
transfer of energy between the working fluid and the rotor, the
fluid is returned to the rotor blades via a return duct or stator
vanes for readmission to the blades and another energy transfer
process takes place. This mode of operation can be continued so
that multi-stage performance is approached with only one rotor.
However, reentry machines have a number of disadvantages including
the presence of interstage leakage and the restriction of the flow
to a specific, single path of the return ducts or stator guide
vanes for all load conditions which permanently fixes the number of
passes made by the fluid through the blades.
In other apparatus of the prior art, the fluid moves in and out of
the rotor blade passages in a generally uncontrolled and disorderly
fashion due to lack of stator guidance. Because of the
disorderliness of the flow, these machines are very inefficient and
the net fluid flow through the machine ceases at a relatively low
limiting value of back pressure.
U.S. Pat. No. 3,292,899, issued Dec. 20, 1966 to Hans Egli, one of
the inventors of the present invention, discloses a multi-pass
energy transfer machine representing a major improvement over the
described prior art. Machines according to the referenced patent
have specific diameter and specific speed characteristics falling
between that of conventional turbomachines and conventional rotary,
positive displacement machines and overlapping considerably into
the latter category. A further advantage of machines of the cited
patent is that they will produce, for a given tip speed, a much
higher head than conventional turbomachines, the term "head" being
defined as the energy transfer per pound of fluid.
The fluid energy transfer machine according to one embodiment of
the referenced patent includes a casing having inlet and outlet
openings and a plurality of blades arranged in cascade fashion on a
rotor for movement in succession past the inlet and outlet
openings. The housing has a smooth interior wall devoid of stator
vanes and is so configured that the fluid in passing from the inlet
opening to the outlet opening is constrained by the walls of the
casing to flow in a generally helicoidal pattern about a stator
ring and through the blade cascade a number of times. The geometry
of the fluid path is primarily dictated by the shapes of the casing
and stator ring, the manner in which the fluid is introduced into
the housing (as determined by the shape and orientation of the
inlet passage leading to the inlet opening) and the circumferential
pressure gradient which, in turn, depends on the back pressure
applied to the machine. Thus, the pitch of the helicoidal flow path
at any specific meridional section of the machine and the total
number of times that the fluid passes through the blade cascade are
functions of back pressure. In order to obtain a practical level of
energy transfer, the fluid should pass at least twice through the
cascade. In the case of a compressor, for example, for any fluid
(whether compressible or incompressible), if the back pressure is
increased while a given rotor speed is maintained, then the number
of passes of the fluid through the blade cascade increases. The
fluid flow pattern is orderly and remains so even though the back
pressure is increased to relatively high levels.
In the prior art machines discussed above, comparatively little
attention is paid, from a fluid dynamics standpoint, to the shaping
of the rotor blades and their position in the flow passage. This is
also true of the block seal separating the inlet and outlet
openings. Thus, the overall efficiency of the machine is not
optimized. The influence on the performance of the machine of the
geometrical configurations and positions of the blades and block
seal has not been adequately appreciated in the prior art.
SUMMARY OF THE INVENTION
Broadly, the present invention comprises an improvement of the
turbomachine disclosed in U.S. Pat. No. 3,292,899, referenced
above, and among its primary objects are the enhancement of the
performance and the structural simplification of that type of
machine.
According to one specific, exemplary form of the invention, there
is provided a casing defining an interior, smooth-walled toroidal
space positioned generally concentric of a central axis of rotation
and having substantially circular meridional cross-sections. Inlet
and outlet passages formed integrally with the casing communicate
with the interior of the casing through inlet and outlet opening
situated in close proximity to one another circumferentially.
The casing encloses a stator ring of generally circular meridional
cross-section. The ring is positioned concentric of the rotational
axis and is spaced from the interior wall surface of the casing to
define a generally annular fluid passage extending
circumferentially about the axis of rotation. The stator ring is
disposed relative to the casing such that the meridional
cross-section of the ring is eccentric with respect to the
meridional cross-section of the toroidal space defined by the
casing, the ring being situated somewhat closer to the outer
extremity of the toroidal space with respect to the axis of
rotation. According to one embodiment, the stator ring is supported
at a plurality of circumferentially spaced points by axially
extending studs attached to the casing.
The inlet and outlet openings are separated by a block seal formed
integral with the stator ring and having side surfaces coinciding
with meridional planes.
The block seal is recessed to form a notch blending smoothly with
the outlet passage to minimize losses and disturbances and to
permit passage of the blade cascade.
The inlet passage is shaped and positioned to direct the fluid into
the annular fluid passage so that a helicoidal motion is initiated
and the outlet is configured to receive the discharging fluid with
minimal losses. In the exemplary form of the invention under
consideration, the inlet passage is positioned to direct the fluid
generally along meridional planes so that at the predominate
operating condition, the absolute velocity vectors of the fluid
approach the blades at approximately 90.degree. with respect to the
direction of blade rotational velocity. The exhaust passage is
oriented approximately in alignment with the absolute velocity
vector of the exiting flow.
The casing also encloses a rotor having a blade cascade in close
running clearance with the stator ring and extending in cantilever
fashion from the rotor approximately parallel with the axis of
rotation. The blades are cambered, aerodynamic sections with chord
lines oriented at a predetermined stagger angle. The fluid flows in
the above-mentioned generally helicoidal path about the stator ring
and is impelled (in the case of a pump, blower or compressor)
during each pass of the fluid through the blade cascade. In this
fashion, the inlet and outlet passages introduce and receive the
fluid from opposite sides of the cascade.
Each blade has a leading edge and a trailing edge extending
generally parallel with the axis of rotation of the machine.
According to an aspect of the invention, the edge nearer the axis
of rotation is longer than the edge further from the axis of
rotation. Thus, in the case of an "outflow" machine in which the
fluid flows away from the axis of rotation during its passage
through the blades, the leading edge of the blade is longer than
the trailing edge. The reverse is true for an "inflow" machine.
According to another significant aspect of the invention, the
geometries and relative positions of the blades and annular fluid
passage are such that the radial distance from the axis of rotation
of the centroid of the meridional cross-section of the annular
passage is larger than the radial distance from the axis of at
least the major portion of the blade edge closer to the axis and
smaller than the radial distance from the axis of at least the
major portion of the edge further from the axis. This geometry and
relative positioning provides a way to assure that the angle of
incidence, that is, the angle at which the relative velocity vector
of the fluid approaches the blade cascade, will remain nearly
constant over a wide operating range.
According to another aspect of the invention, in order to more
closely satisfy continuity considerations in the case of
compressible fluids, the meridional cross-sectional area of the
annular fluid passage may be designed to decrease (in the case of a
compressor or blower) toward the point of discharge. This may be
accomplished by utilizing a stator ring having a meridional
cross-sectional area which increases from inlet to outlet, or
alternatively, a casing having an interior wall whose meridional
cross-sectional area decreases between inlet and outlet, or a
combination of such geometries.
The invention provides a broad operating range over which high
efficiencies are obtained, and the relatively low operating speed
of machines according to the invention permits the use, for many
applications, of practical drive systems in contrast to
conventional types of turbomachines which require rotational speeds
too high for such drives.
By way of example, the machine of the invention may be designed as
an air pump for use in the emission control systems of automobiles.
Such pumps introduce pressurized, secondary air into the exhaust
stream to provide additional oxygen to insure complete combustion
of the exhaust products. Apparatus according to the invention meets
the cost, minimum bulk, simplicity, and functional and operational
air requirements of such systems.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, advantages and features of the invention will become
apparent by reference to the following detailed description in
conjunction with the accompanying drawings, in which:
FIG. 1 is an exploded, prespective view of an energy transfer
machine, designed for operation as an air pump, in accordance with
the invention;
FIG. 2 is a front elevation view of the machine of FIG. 1;
FIG. 3 is a side elevation view, partly in section, of the machine
of FIG. 1, the section being taken along the broken plane 3--3 in
FIG. 2;
FIG. 4 is a rear view of the macnine of FIG. 1 with certain
portions of the casing omitted for clarity and showing the path of
a typical fluid particle;
FIG. 5 is a front view of a portion of the rotor of the machine of
FIG. 1 showing details of the blade cascade;
FIG. 6 is a representation of a straight blade cascade showing
certain, pertinent geometric interrelationships;
FIG. 7 is a somewhat schematic, meridional cross-section view of a
portion of a machine according to the invention to illustrate
certain geometric relationships for a first, exemplary blade
configuration;
FIG. 8 is a meridional cross-section view similar to that of FIG. 7
showing the same geometric relationships for a second, exemplary
blade configuration;
FIG. 9 is a rear view of an alternative embodiment of the energy
transfer machine of the invention, designed for use as an air pump,
with certain portions of the machine omitted for clarity;
FIG. 10 is a cross-section view of a portion of the apparatus of
FIG. 9 as seen along the plane 10--10;
FIG. 11 is a cross-section view of a portion of the apparatus of
FIG. 9 as seen along the plane 11--11;
FIG. 12 is a rear view of another alternative embodiment of the
energy transfer machine of the invention, designed for operation as
an air pump, with certain portions of the machine omitted for
clarity;
FIG. 13 is a cross-section view of a portion of the apparatus of
FIG. 1 as seen along the plane 13--13;
FIG. 14 is a front elevation view of an energy transfer machine
according to still another embodiment of the invention;
FIG. 15 is a rear elevation view of the machine of FIG. 14 with
certain portions thereof omitted for clarity;
FIG. 16 is a cross-section view of a portion of the machine of FIG.
14 taken along the plane 16--16 in FIG. 15;
FIG. 17 is a side elevation view in cross-section of the machine of
FIG. 14 taken along the broken plane 17--17 in FIG. 15;
FIG. 18 is a top view of a portion of the machine of FIG. 14
showing details of the block seal; and,
FIG. 19 is a block diagram of an internal combustion engine and
associated emission control system having a secondary air pump
constructed pursuant to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Although it will be apparent to those skilled in the art that
machines according to the present invention can be constructed for
operation as pumps, blowers, compressors, turbines, and so forth,
utilizing either gas or liquid as the working fluid medium, for
purposes of illustration the drawings and ensuing description are
directed to an embodiment of the invention which has application as
an air pump and is particularly useful as a source of pressurized
secondary air in automobile emission control system.
Turning now to FIGS. 1-5 of the drawings, there is shown a machine
exemplifying the present invention and including generally a casing
10 and a rotor 12 both concentric of a central axis of rotation
14.
The casing 10 is composite, split structure consisting basically of
a front casing portion 16 and a rear casing portion 18 joined along
an interface extending generally transverse of the axis 14. The
front casing portion 16 defines an axially extending cylindrical
bore 20 enclosing a shaft 22 supported by a pair of ball bearings
24. The rotor 12 is attached to the rear extremity of the shaft 22
for rotation about the axis 14. The front casing portion 16 also
includes a radially oriented inlet passage 26 shaped and positioned
symmetrically about a meridional plane 28. The inlet passage 26
communicates with the casing interior through an inlet opening 29.
The rear casing portion 18 includes an outlet passage 30 and
associated outlet opening 31. The passage 30 is oriented so as to
be in approximate alignment with the absolute velocity vectors of
the fluid approaching the outlet opening 31.
The casing 10 also encloses an annular, intermediate casing portion
32 concentric of the axis 14 and positioned between the front and
rear casing portions 16 and 18. The casing portions 16, 18 and 32
have smooth, arcuate interior surfaces 34, 36 and 38, respectively.
Except for an annular opening 40 between the rear portion 18 and
the intermediate portion 32, the surfaces 34, 36 and 38 are
contiguous and together define a smooth-walled, toroidal volume or
space whose axis of revolution is the axis 14. In meridional
cross-section, as shown in FIG. 3 for example, the toroidal space
has a generally circular appearance, the exact geometry depending
upon many parameters including flow rate, rotor speed, pressure
ratio, type of fluid, and so forth. For particular applications,
the shape of the toroidal space, in meridional cross-section, may
be varied as required, for example, it may be elongated in a given
direction such as in the direction of the axis of rotation.
Disposed inside the toroidal space defined by the casing 10 is a
stator ring 42, which, in the example shown, has a generally
circular meridional cross-section. The stator ring 42 is fastened
to the front casing portion 16 by three studs 44 and is spaced from
the interior wall surfaces 34, 36 and 38 so as to define conjointly
with these surfaces an annular fluid passage 46 having a meridional
cross-section that is uniform about the axis 14. The ring 42, as
best seen in FIGS. 3 and 4, is positioned within the toroidal space
so as to be somewhat closer to the outer extremities of that space.
Like the toroidal space in which it is enclosed, the configuration
of the meridional cross-section of the ring 42 may be varied from
that shown in the drawings as required for particular
applications.
The rotor 12 comprises a disk 50 transverse of the axis 14 and
having along its outer periphery a forwardly projecting rim 52
extending parallel with the axis 14 into the annular opening 40.
Outer and inner rim seals 54 and 56, respectively, on the rear and
intermediate casing portions 18 and 32 preserve the circumferential
pressure gradient within the casing during operation of the
machine. Attached to forward extremity of the rim 52 in cantilever
fashion is a cascade of spaced blades 60. As shown in FIGS. 3 and
also with reference to FIG. 7, each blade 60 has an inner edge 62,
an outer edge 64, a base 66 and a tip 68. In the particular example
shown, the edges 62 and 64 are approximately parallel with the axis
14 but it is to be noted that the blades are not limited to that
specific configuration. The edges 62 and 64 may to some extent be
out of parallelism with respect to each other and the axis 14 to
achieve specific performance characteristics and/or facilitate
manufacture of the rotor. With respect to the latter in particular,
the orientation of the blade edges approximately parallel with the
axis of rotation makes possible the use of a simple, two-part die
for casting the rotor as a single piece. To facilitate separation
of such a die, the blade edges may be provided with "draft," that
is, the edges may converge toward the tip at a small angle.
In the specific example shown, the stator ring 42 has a machined,
conical face 74 positioned immediately adjacent the blade tips 68.
The tips 68 have a linear configuration and slope relative to the
axis 14 so as to be parallel with the conical face 74 as viewed in
any meridional cross-section (see FIGS. 3, 7 and 8 in particular).
Thus, a constant, minimum running clearance is maintained along the
entire circumference of the ring 42 about the axis 14 between the
face 74 and the blade tips 68. The surface 74 may be other than
conical so long as it conforms to the contour of the blade tips and
is separated therefrom by a constant, minimum running
clearance.
As shown in FIG. 5, each blade 60 has a cambered, airfoil
configuration and is set at a stagger angle .phi. defined by a
typical blade chord line 80 and a meridional plane 82 tangent to
the trailing edge 64 of the blade. According to one specific
example, the stagger angle .phi. is approximately 12.degree. and
there are a total of 72 blades.
From the standpoint of optimizing the performance of the machine,
it is desirable to maintain a constant angle of incidence over a
broad operating range. For purposes of the present invention, the
definition of "angle of incidence" may be understood by reference
to FIG. 6 which shows a straight cascade of blades 90. The
representation in FIG. 6 may be thought of as a portion of the
blade cascade on a rotor of infinite radius with the plane of the
drawing coinciding with a plane normal to the axis of rotation.
Each blade 90 has a leading edge 92 and a camber line or mean line
94 about which the blade surfaces are constructed. The angle of
incidence, .beta., is defined as the angle between a line 96 drawn
tangent to the mean line 94 at the leading edge 92 and the vector
V.sub.R which is the component of the relative velocity of the
fluid approaching the cascade in a plane normal to the axis of
rotation.
With reference now to FIGS. 7 and 8, the maintenance of a nearly
constant angle of incidence over a wide range of operation is
achieved pursuant to this invention by positioning the blades so
that, as viewed in a typical meridional cross-section, the radial
distance from the axis of rotation of the centroid of the
meridional cross-section of the annular fluid passage lies in
between the radial distances from the axis of rotation of at least
the major portions of the inner and outer edges of the blades. The
term "annular fluid passage," as used throughout this application,
encompasses the entire passage about the stator ring including that
portion of the passage traversing the blade cascade.
Thus, in FIG. 7, which is an enlargement of a typical meridional
cross-section of the machine shown in FIGS. 1-4, the radial
distance, r.sub.2, from the axis of rotation 14 of the centroid 98
of the meridional cross-section of the annular fluid passage 46 is
greater than the radial distance r.sub.1 from the axis 14 to the
inner blade edge 62 and less than the radial distance r.sub.3 from
the axis 14 to the outer blade edge 64.
In the embodiment of FIG. 7, the edges 62 and 64 are parallel with
the axis 14 so that the centroid 98 lies between the entire extents
of the edges 62 and 64. In contrast, in FIG. 8 there is shown a
meridional cross-section configuration of a machine including
blades 60a each having inner and outer edges 62a and 64a,
respectively, that converge toward the blade tip so as to be
non-parallel with respect to each other and the axis of rotation
14a. In this case, the radial distance, r.sub.2 ', of the centroid
98a of the meridional section of the annular fluid passage 46a
intersects the inner blade edge 62a. However, in accordance with
the principles of the invention, all points along at least a major
portion, p, of the length of the inner edge 62a lie at a radial
distance r.sub.1 ' from the axis 14a that is less than the radial
distance r.sub.2 '. Further, in the example of FIG. 8, the entire
length of the outer edge 64a lies outside the radial distance
r.sub.2 ' to the centroid 98a.
Another geometric interrelationship forming an aspect of the
present invention and which aids in achieving high performance and
efficiency is that the inner edges of the blades (such as the edge
62) are longer than the outer edges (such as the edge 64). This, of
course, is a reflection of the geometry of the annular fluid
passage 46 whose radially outward portions are narrower than the
radially inward portions. Stated another way, the blade cascade, in
a general sense, separates the wider, radially inward regions of
the annular passage 46 from the narrower, radially outward regions.
This geometry, in cooperation with the circumferential pressure
gradient, results in a rise of static pressure (in the case of a
compressor) as the fluid moves from inlet to outlet.
Separating the inlet and outlet openings 29 and 31 is a block seal
100 which, as shown in FIGS. 3 and 4, fills and seals the entire
fluid passage along a short sector, the length of which is at least
equal to the spacing between adjacent blades. The inlet and outlet
openings 29 and 31 are immediately adjacent the block seal 100 so
as to be in close proximity to one another. The block seal 100 is
preferably fabricated as an integral part of the stator ring 42 and
in this specific embodiment has flat side faces 102 and 104 which
coincide with meridional planes. The block seal 100 further has an
arcuate recess 106 to permit passage of the blade cascade, the
forward surface 108 of the recess 106 being flush with the face 74
on the stator ring. The recess 106 is dimensioned so that a minimum
running clearance is provided for passage of the blade cascade.
The block seal 100 also has a U-shaped, angularly oriented notch
110 fairing smoothly into the outlet passage 30 to minimize
losses.
With reference to FIG. 4 which shows, for a compressor, a typical
streamline 114, that is, the path of a typical fluid particle, the
fluid particle enters the inlet passage 26 and is directed thereby
in a generally radial direction through the inlet opening 29 and
under the stator ring 42. The fluid, following a generally
helicoidal path, then enters the blade cascade at point A nearly
perpendicular to the blade rotational direction. The energy level
of the fluid is increased as a result of the work done by the
blades on the fluid and this increase in energy level is seen
mostly as an increase in absolute velocity and a small increase in
static pressure. As the fluid leaves the blades at point B and
circulates about the stator ring to the point C, a further pressure
increase occurs as a consequence of the diffusing action which
converts kinetic energy (energy associated with velocity) into
static pressure. This diffusing action is a result of the
increasing pressure as the fluid advances circumferentially about
the axis 14. The fluid, entering at point C, then passes through a
portion of the blade cascade a second time and the process may
repeat itself several times before the fluid exits via the outlet
passage 30. The fluid, at all times, follows a smooth, orderly,
generally helicoidal path about the stator ring 42 and in the case
of a compressible fluid processed by a machine having an annular
fluid passage of constant cross-sectional area, that is, a passage
defined by a surface of revolution about the rotational axis 14,
the pitch of the generally helicoidal path 114 decreases as the
fluid moves circumferentially about the axis 15 into regions of
higher pressure.
The particular embodiment under discussion may be designated as an
"outflow" machine in which the fluid moves through the blade
cascade in a direction away from the axis 14. The inner edges 62
thus function as the leading edges of the blade while the outer
edges 64 are the trailing edges. It will be appreciated that it is
possible, with obvious modifications based on the disclosure
herein, to reverse the fluid flow direction so that an "inflow"
pattern is established in which the fluid moves toward the axis 14
during its traversal of the blade cascade. In that case, the outer
edge becomes the leading edge and the inner edge functions as the
trailing edge.
Turning now to FIGS. 9 through 13, there is shown a pair of
alternative embodiments the construction of which is such that the
meridional cross-section area of the fluid passage is gradually
decreased between inlet and outlet so as to enhance the efficiency
of the machine when compressible fluids, such as air, are
processed. In the embodiment of FIGS. 9-11, the meridional
cross-section area of the stator ring 120 is gradually increased
between the inlet and outlet ends, the inlet end 122 having a
relatively small cross-section area and the outlet end 124 having a
relatively large cross-section area. All of the other geometric
considerations discussed above are retained in this version for
high performance and high efficiency operation.
In FIGS. 12 and 13, the meridional cross-section area of the
interior wall 130 of the casing 132 is gradually decreased so as to
obtain the same result as that accomplished with the embodiment of
FIGS. 9-11. The meridional cross-section near the inlet end appears
as shown in FIG. 10 and FIG. 13 shows a typical section near the
outlet. In this embodiment, the stator ring 134 has a uniform
meridional cross-section area along its entire length. It will be
obvious that a combination of the configurations of FIGS. 9-11 and
12-13 may be used, that is, both the meridional cross-section area
of the stator ring may be increased and the meridional
cross-section area of the interior wall of the casing may be
decreased gradually between inlet and outlet.
The above-described geometry and orientation of the blades, the
orientation and positions of the inlet and outlet passages relative
to each other and to the block seal, and the small number or parts
required, all contribute, in comparison to the prior art, to
furnish a compact, high performance, simple and low cost fluid
energy transfer machine.
Further structural simplifications may be achieved by fabricating
the intermediate casing portion, the stator ring and the block seal
as a one-piece casting. Such an arrangement, along with certain
additional modifications, is shown in the embodiment of FIGS.
14-18. This embodiment of the invention comprises a casing 140
enclosing a rotor 142 mounted on a shaft 144 carried by ball
bearings 146 for rotation about a central axis 148. The rotor has a
cascade of blades 149 similar to those already described. The
casing 140 includes a front portion 150, an intermediate ring-like
portion 152 and a rear portion 154 joined to the front portion 150
about the outer periphery of the machine. The casing portions 150,
152 and 154 and an arcuate surface 156 on the rotor 142 together
define a smooth-walled, interior wall surface 158 having a shape as
described in connection with previously discussed embodiments.
The casing 140 encloses a stator ring 160 defining with the wall
surface 158 an annular fluid passage 161. The ring 160 includes as
an integral part thereof, a block seal 162 having an outer surface
164 conforming closely to the configuration of the interior wall
surface 158. As shown in FIGS. 15 and 18, a part of the surface 164
comprises the periphery of a flange 166 having spaced, radially
oriented portions 168 and 170 having side surfaces lying in
meridional planes. The flange 166 further includes an undulation
172 which functions both to reduce the acoustic level during
operation and to define a notch that blends into the outlet passage
174 to minimize losses. The surface 164 may be grooved along its
length, as indicated in the drawings by the reference numeral 176,
or alternatively, may be smooth; in either case, appropriate
sealing means is applied to the surface 164 so that a leak-tight
joint is provided and the stator ring is securely held in
place.
The intermediate casing portion 152 is supported by two or more
ribs 178 projecting inwardly from the stator ring. In this way, the
ring 160, the intermediate casing portion 152 and the ribs 178 may
all be formed as a single casting. Alternatively, studs (such as
studs 44 in the embodiment of FIGS. 1-4) may be used in place of,
or in conjunction with, the ribs 178. As a further structural
simplification, the inner rim seal (reference numeral 56 in FIG. 3)
is replaced by a transverse face seal 180 between the rotor and
intermediate casing portion extending normal to the axis 148.
The front casing portion 150 defines a circumferential, axially
extending chamber 184 including an enlarged inlet passage 186
communicating with the annular fluid passage 161 through an inlet
opening 188. The opening 188 extends a short arcuate distance (for
example about 60.degree.) about the axis 148 and is positioned
immediately adjacent the block seal 162. The chamber 184 tapers
outwardly toward the rear of the machine and is divided into
sections by three longitudinal partitions 190, the chamber sections
communicating with each other and the inlet passage 186 through
openings 192 behind the partitions 190. Fluid is introduced int the
chamber 184 through a centrifugal dirt separator 194, the operation
and structure of which are well known in the art, and a series of
arcuate intake ports 196. A web 198, centrally positioned within
the intake passage 186 strengthens the front casing portion and
assists in directing the incoming fluid.
The fluid entering the chamber 184 has a relatively high absolute
velocity as represented by the vector V.sub.1. The outwardly
tapering configuration of the chamber 184 provides a diffusing
characteristic so that the fluid entering the annular fluid passage
161 will have a lower absolute velocity, represented by the vector
V.sub.2. Thus, one function of the chamber 184 is to minimize
losses by making the velocity V.sub.2 required at the inlet opening
188 compatible with the velocity V.sub.1 produced by the dirt
separator 194. The configuration of the chamber 184 and the
presence of the web 198 serve to direct the fluid approaching the
inlet opening 188 generally along meridional planes so that the
fluid enters the blades 149 approximately perpendicular to the
direction of blade movement, similar to that described in
connection with the inlet passage 26 of the embodiment of FIGS.
1-4. The passage 174 is oriented in the same direction as the
outlet passage 30 of the above-mentioned embodiment.
To illustrate an application of the present invention, FIG. 19 is a
schematic representation of an automobile internal combustion
engine 210 and associated emission control system. The emission
control system shown is typical of the systems currently under
consideration for general use by the automotive industry to comply
with clean air standards and includes a thermal reactor 212
connected to exhaust passages 214, a catalytic converter 216 and a
muffler 218. An air pump 220, which may be of the type disclosed
herein, is directly driven by the engine 210 and supplies secondary
air under pressure to the exhaust passages 214 via a flow
controller 222.
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