Information
-
Patent Grant
-
6425732
-
Patent Number
6,425,732
-
Date Filed
Tuesday, August 22, 200024 years ago
-
Date Issued
Tuesday, July 30, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Look; Edward K.
- McAleenan; James M
Agents
-
CPC
-
US Classifications
Field of Search
US
- 415 551
- 415 552
- 415 553
- 415 1736
- 415 228
- 416 189
- 029 88921
- 029 447
- 029 40705
-
International Classifications
-
Abstract
A method of combining an impeller and a shroud includes selecting a rotatable impeller having impeller blades with radially extending distal ends defining a predetermined outer impeller diameter. A shroud element is then selected having an inner diameter less than the outer impeller diameter. The shroud element is then attached to at least some of the radially extending distal ends of the impeller blades by forming an interference fit between the inner shroud diameter and the outer impeller diameter.
Description
TECHNICAL FIELD
The present invention relates to a method of manufacturing an impeller element having a shroud attached to the impeller blades, and particularly to a compressor/turbine permanent magnet motor/generator having a shroud attached to the impeller blades by an interference fit therebetween.
BACKGROUND ART
A helical flow compressor is a high-speed rotary machine that accomplishes compression by imparting a velocity head to each fluid particle as it passes through the machine's impeller blades and then converting that velocity head into a pressure head in a stator channel that functions as a vaneless diffuser. While in this respect a helical flow compressor has some characteristics in common with a centrifugal compressor, the primary flow in a helical flow compressor is peripheral and asymmetrical, while in a centrifugal compressor, the primary flow is radial and symmetrical. The fluid particles passing through a helical flow compressor travel around the periphery of the helical flow compressor impeller within a generally horseshoe shaped stator channel. Within this channel, the fluid particles travel along helical streamlines, the centerline of the helix coinciding with the center of the curved stator channel. This flow pattern causes each fluid particle to pass through the impeller blades or buckets many times while the fluid particles are traveling through the helical flow compressor, each time acquiring kinetic energy. After each pass through the impeller blades, the fluid particles reenter the adjacent stator channel where they convert their kinetic energy into potential energy and a resulting peripheral pressure gradient in the stator channel.
The multiple passes through the impeller blades (regenerative flow pattern) allows a helical flow compressor to produce discharge heads of up to fifteen (15) times those produced by a centrifugal compressor operating at equal tip speeds. Since the cross-sectional area of the peripheral flow in a helical flow compressor is usually smaller than the cross-sectional area of the radial flow in a centrifugal compressor, a helical flow compressor would normally operate at flows which are lower than the flows of a centrifugal compressor having an equal impeller diameter and operating at an equal tip speed. These high-head, low-flow characteristics of a helical flow compressor make it well suited to a number of applications where a reciprocating compressor, a rotary displacement compressor, or a low specific-speed centrifugal compressor would not be as well suited.
A helical flow compressor can be utilized as a turbine by supplying it with a high pressure working fluid, dropping fluid pressure through the machine, and extracting the resulting shaft horsepower with a generator. Hence the term “compressor/turbine” which is used throughout this application.
Among the advantages of a helical flow compressor or a helical flow turbine are:
(a) simple, reliable design with only one rotating assembly;
(b) stable, surge-free operation over a wide range of operating conditions (i.e. from full flow to no flow);
(c) long life (e.g., 40,000 hours) limited mainly by their bearings;
(d) freedom from wear product and oil contamination since there are no rubbing or lubricated surfaces utilized;
(e) fewer stages required when compared to a centrifugal compressor; and
(f) higher operating efficiencies when compared to a very low specific-speed (high head pressure, low impeller speed, low flow) centrifugal compressor.
On the other hand, a helical flow compressor or turbine cannot compete with a moderate to high specific-speed centrifugal compressor, in view of their relative efficiencies. While the best efficiency of a centrifugal compressor at a high specific-speed operating condition would be on the order of seventy-eight percent (78%), at a low specific-speed operating condition of a centrifugal compressor could have an efficiency of less than twenty percent (20%). A helical flow compressor operating at the same low specific-speed and at its best flow can have efficiencies of about fifty-five percent (55%) with curved blades and can have efficiencies of about thirty-eight percent (38%) with straight radial blades.
The flow in a helical flow compressor can be visualized as two fluid streams which first merge and then divide as they pass through the compressor. One fluid stream travels within the impeller buckets and endlessly circles the compressor. The second fluid stream enters the compressor radially through the inlet port and then moves into the horseshoe shaped stator channel which is adjacent to the impeller buckets. Here the fluids in the two streams merge and mix. The stator channel and impeller bucket streams continue to exchange fluid while the stator channel fluid stream is drawn around the compressor by the impeller motion. When the stator channel fluid stream has traveled around most of the compressor periphery, its further circular travel is blocked by the stripper plate. The stator channel fluid stream then turns radially outward and exits from the compressor through the discharge port. The remaining impeller bucket fluid stream passes through the stripper plate within the buckets and merges with the fluid just entering the compressor/turbine.
The fluid in the impeller buckets of a helical flow compressor travels around the compressor at a peripheral velocity which is essentially equal to the impeller blade velocity. It thus experiences a strong centrifugal force which tends to drive it radially outward, out of the buckets. The fluid in the adjacent stator channel travels at an average peripheral velocity of between five (5) and ninety-nine (99) percent of the impeller blade velocity depending upon the compressor discharge flow. It thus experiences a centrifugal force which is much less than that experienced by the fluid in the impeller buckets. Since these two centrifugal forces oppose each other and are unequal, the fluid occupying the impeller buckets and the stator channel is driven into a circulating or regenerative flow. The fluid in the impeller buckets is driven radially outward and “upward” into the stator channel. The fluid in the stator channel is displaced and forced radially inward and “downward” into the impeller bucket.
The fluid in the impeller buckets of a helical flow turbine travels around the turbine at a peripheral velocity which is essentially equal to the impeller blade velocity. It thus experiences a strong centrifugal force which would like to drive it radially outward if unopposed by other forces. The fluid in the adjacent stator channel travels at an average peripheral velocity of between one hundred and one percent (101%) and two hundred percent (200%) of the impeller blade velocity, depending upon the compressor discharge flow. It thus experiences a centrifugal force which is much greater than that experienced by the fluid in the impeller buckets. Since these two centrifugal forces oppose each other and are unequal, the fluid occupying the impeller buckets and the stator channel is driven into a circulating or regenerative flow. The fluid in the impeller buckets is driven radially inward and “upward” into the stator channel. The fluid in the stator channel is displaced and forced radially outward and “downward” into the impeller bucket.
While the fluid is traveling regeneratively, it is also traveling peripherally around the stator-impeller channel. Thus, each fluid particle passing through a helical flow compressor or turbine travels along a helical streamline, the centerline of the helix coinciding with the center of the generally horseshoe shaped stator-impeller channel.
While the unique capabilities of a helical flow compressor would seem to offer many applications, the low flow limitation has severely curtailed their widespread utilization.
Permanent magnet motors and generators, on the other hand, are used widely in many varied applications. This type of motor/generator, such as in U.S. Pat. No. 5,899,673, has a stationary field coil and a rotatable armature of permanent magnets. In recent years, high energy product permanent magnets having significant energy increases have become available. Samarium cobalt permanent magnets having an energy product of twenty-seven (27) megagauss-oersted (mgo) are now readily available and neodymium-iron-boron magnets with an energy product of thirty-five (35) megagauss-oersted are also available. Even further increases of mgo to over 45 megagauss-oersted promise to be available soon. The use of such high energy product permanent magnets permits increasingly smaller machines capable of supplying increasingly higher power outputs. The permanent magnet rotor may comprise a plurality of equally spaced magnetic poles of alternating polarity or may even be a sintered one-piece magnet with radial orientation. The stator would normally include a plurality of windings and magnet poles of alternating polarity. In a generator mode, rotation of the rotor causes the permanent magnets to pass by the stator poles and coils and thereby induces an electric current to flow in each of the coils. In the motor mode, electrical current is passed through the coils which will cause the permanent magnet rotor to rotate.
In various rotating impeller designs, shrouds have been added to improve aerodynamic performance of the blades. For example, shrouds have been attached to the impeller blades by casting large impeller blades which are thick enough to locally receive a screw to attach the shroud. This type of attachment requires a relief hole through which the screw is inserted. The relief hole requires close tolerances, which can be burdensome and costly to the manufacturing process. This method generally only works for large impellers and is not desirable for a small thin impeller, as implemented in a permanent magnet motor/generator or a small gas turbine engine.
Accordingly, it is desirable to provide a method of attaching a shroud to a small impeller in a manner in which manufacturing costs are minimized and part quality and strength are enhanced.
SUMMARY OF THE INVENTION
The present invention overcomes the above-referenced shortcomings of prior art shroud/impeller assemblies by providing a shroud which is attached to an impeller by an interference fit.
Specifically, the present invention improves upon the compressor/turbine permanent magnet motor/generator of U.S. Pat. No. 5,899,673, and the efficiency of the ‘
673
invention by controlling fluid flow with a shroud attached to the impeller. To accomplish such an improvement, this invention incorporates: a housing including first and second stators positioned within the housing and having respective channels cooperating to define a substantially annular pathway within the housing; a shaft rotatably supported within the housing; a rotatable element mounted for rotation with the shaft and having impeller blades substantially within the pathway, the impeller blades having respective radially extending distal ends defining an outer impeller diameter; and a shroud surrounding the rotatable element and connected thereto by an interference fit with at least some of the distal ends, the shroud in transverse cross-section having one configuration at the interference fit and another configuration outwardly thereof, whereby the other configuration cooperates with the channels of the first and second stators to define a helical pathway around the shroud.
Therefore, it is an object of the present invention is to attach the shroud to the impeller with an interference fit. This may be accomplished by either heating and cooling the shroud to be placed in juxtaposition to the impeller blades, or, alternatively, by forcing the shroud over the impeller blades.
Additionally, it is an object that the shroud in transverse cross-section may comprise a rounded portion which engages flowing fluid to encourage smooth fluid flow and discourage separation of the fluid from the shroud.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
Having thus described the present invention in general terms, reference will now be made to the accompanying drawings in which:
FIG. 1
is an end view of a single stage helical flow compressor/turbine permanent magnet motor/generator in which the impeller/shroud of the present invention may be implemented;
FIG. 2
is a cross sectional view of the helical flow compressor/turbine permanent magnet motor/generator of
FIG. 1
taken along line
2
—
2
;
FIG. 3
is a cross sectional view of the helical flow compressor/turbine permanent magnet motor/generator of
FIG. 1
taken along line
3
—
3
;
FIG. 4
is an enlarged sectional view of a portion of the helical flow compressor/turbine permanent magnet motor/generator of
FIG. 2
;
FIG. 5
is an enlarged sectional view of a portion of the helical flow compressor/turbine permanent magnet motor/generator of
FIG. 3
;
FIG. 6
is an enlarged partial plan view of the helical flow compressor/turbine impeller having straight radial blades and illustrating the flow of fluid therethrough;
FIG. 7
is an enlarged partial plan view of a helical flow compressor/turbine impeller having curved blades;
FIG. 8
is a perspective view of a stator channel plate of the helical flow compressor/turbine permanent magnet motor/generator of
FIGS. 1-5
;
FIG. 9
is an enlarged sectional view of a portion of
FIG. 5
illustrating fluid flow streamlines in the impeller blades and fluid flow stator channels;
FIG. 10
is a schematic representation of the flow of fluid through a helical flow compressor/turbine;
FIG. 11
shows a cut-away perspective view of a radial flow compressor in accordance with the present invention;
FIG. 12
shows a schematically arranged sectional view of a shroud and impeller in a radial flow compressor, such as that shown in
FIG. 11
;
FIG. 13
shows a plan view of an impeller in accordance with the present invention;
FIG. 14
shows a sectional view taken at line
14
—
14
of
FIG. 13
;
FIG. 15
shows perspective view of the impeller of
FIG. 13
;
FIG. 16
shows a plan view of an impeller and shroud in accordance with the present invention;
FIG. 17
shows a sectional view taken at line
17
—
17
of
FIG. 16
; and
FIG. 18
shows a perspective view of the impeller and shroud of FIG.
16
.
BEST MODE FOR CARRYING OUT THE INVENTION
A single stage helical flow compressor/turbine permanent magnet motor/generator
10
is illustrated in
FIGS. 1-3
, as described in U.S. Pat. No. 5,899,673, and is a preferred environment in which an impeller in accordance with the present invention may be implemented. The permanent magnet motor/generator
10
includes a fluid inlet
12
to provide fluid to the helical flow compressor/turbine
14
of the helical flow compressor/turbine permanent magnet motor/generator
10
and a fluid outlet
16
to remove fluid from the helical flow compressor/turbine
14
of the helical flow compressor/turbine permanent motor/generator
10
. The helical flow machine is referred to as a compressor/turbine since it can function both as a compressor and as a turbine. The permanent magnet machine is referred to as a motor/generator since it can function equally well as a motor to produce shaft horsepower or as a generator to produce electrical power.
The helical flow compressor/turbine permanent magnet motor/generator
10
includes a shaft
20
rotatably supported by bearings
21
and
22
. The position of bearing
22
is maintained by two back-to-back Belleville type washers
25
which also prevent rotation of the outer bearing race. An impeller
23
is mounted at one end of the shaft
20
, while permanent magnet rotor
27
is mounted at the opposite end thereof between bearings
21
and
22
.
A stripper plate
26
is disposed radially outward from impeller
23
. The permanent magnet rotor
27
on the shaft
2
disposed to rotate within stator
28
having electrical conductors which is disposed in the permanent magnet housing
29
.
The impeller
23
is disposed to rotate between stator channel plate
32
and stator channel plate
33
. The stripper plate
26
has a thickness slightly greater than the thickness of impeller
23
to provide a running clearance for the impeller
23
between stator channel plates
32
and
33
. Stator channel plate
32
includes a generally horseshoe shaped fluid flow stator channel
38
having an inlet to receive fluid from the fluid inlet
12
. Stator channel plate
33
also includes a generally horseshoe shaped fluid flow stator channel
40
which mirrors the generally horseshoe shaped fluid flow stator channel
38
in the stator channel plate
32
.
Each of the stator channels
38
and
40
include an inlet
45
and an outlet
46
disposed radially outward from the channel. The inlets and outlets of generally horseshoe shaped fluid flow stator channel
38
and generally horseshoe shaped fluid flow stator channel
40
are aligned. The fluid inlet
12
extends through stator channel plate
32
and stripper plate
26
to the inlets
45
of both of stator channel plate generally horseshoe shaped fluid flow stator channel
38
and stator channel plate generally horseshoe shaped fluid flow stator channel
40
. The fluid outlet
16
extends from the outlets
46
of both stator channel plate generally horseshoe shaped fluid flow stator channel
38
and stator channel plate generally horseshoe shaped fluid flow stator channel
40
.
The fluid flow stator channels are best illustrated in
FIG. 8
which is a perspective view of the stator channel plate
33
. The generally horseshoe shaped stator channel
40
is shown along with inlet
45
and outlet
46
. The inlet
45
and outlet
46
for a single stage helical flow compressor/turbine would normally be relatively displaced approximately thirty (30) degrees. An alignment or locator hole
47
is provided in each of the stator channel plates
32
and
33
and the stripper plate
26
. The inlet
45
is connected to the generally horseshoe shaped stator channel
40
by a converging nozzle passage
41
that converts fluid pressure energy into fluid velocity energy. Likewise, the other end of the generally horseshoe shaped stator channel
40
is connected to the outlet
46
by a diverging diffuser passage
42
that converts fluid velocity energy into fluid pressure energy.
The depth and cross-sectional flow area of fluid flow stator channel
40
are tapered preferably so that the peripheral flow velocity need not vary as fluid pressure and density vary along the fluid flow stator channel. When compressing, the depth of the fluid flow stator channel
40
decreases from inlet to outlet as the pressure and density increases. Converging nozzle passage
41
and diverging diffuser passage
42
allow efficient conversion of fluid pressure energy into fluid velocity energy and vice versa.
In a helical flow compressor/turbine, fluid enters the inlet port
12
, is accelerated as it passes through the converging nozzle passage
41
, is split into two (2) flow paths by stripper plate
26
, then enters the end of a generally horseshoe shaped fluid flow stator channel axially adjacent to the impeller blades
48
. The fluid is then directed radially inward to the root of the impeller blades
48
by a pressure gradient, accelerated through and out of the blades
48
by centrifugal force, from where it re-enters the fluid flow stator channel. During this time the fluid has been traveling tangentially around the periphery of the helical flow compressor/turbine. As a result of this, a helical flow is established as best shown in
FIGS. 6
,
9
, and
10
.
The impeller blades or buckets are best illustrated in
FIGS. 6 and 7
. The radial outward edge of the impeller
23
includes a plurality of low pressure blades
48
. While these blades
48
may be radially straight as shown in
FIG. 6
, there may be specific applications and/or operating conditions where curved blades may be more appropriate or required.
FIG. 7
illustrates a portion of a helical flow compressor/turbine impeller having a plurality of curved blades
50
. The curved blade base or root
51
has less of a curve than the leading edge
52
thereof. The curved blade tip
53
, at both the root
51
and leading edge
52
would be generally radial.
FIG. 9
shows the flow through the impeller blades and the fluid flow stator channels by means of streamlines
43
. On the other hand
FIG. 10
schematically illustrates the helical flow around the centerline of the impeller and fluid flow stator channel. The turning of the flow is illustrated by the alternating solid and open flow pattern lines in FIG.
10
.
An impeller in accordance with the present invention may also be implemented in a two (2) stage or three (3) stage helical flow compressor/turbine permanent magnet motor/generator as described in U.S. Pat. No. 5,899,673, which is hereby incorporated by reference in its entirety.
Turning to
FIGS. 11-18
, the present invention is illustrated wherein a shroud is attached to an impeller by an interference fit, and incorporated within the previously described helical flow compressor/turbine magnet motor/generator, with modifications to the fluid flow stator channels
38
,
40
previously described.
Referring to
FIGS. 11 and 12
, a radial flow compressor
100
is shown in accordance with the present invention, and may be implemented into the helical flow compressor/turbine permanent magnet motor/generator
10
illustrated and described above with reference to
FIGS. 1-10
. This structure is in all other respects similar to the structure described above with reference to
FIGS. 1-10
, except that the impeller
120
is provided with a shroud
110
, and the flow channel
132
is configured accordingly to receive the shroud
110
, as described in greater detail below. In
FIG. 11
, like numerals are used to identify like components, as described previously with reference to
FIGS. 1-10
.
Referring to
FIG. 12
, a shroud
110
is shown in combination with a rotatable impeller element
120
. The rotatable impeller
120
has impeller blades
118
, and is attached to a shaft
20
of a helical flow compressor/turbine, such as that shown in FIG.
2
. The shroud
110
is attached by an interference fit to the impeller blades
118
, and surrounded by a first wall
128
of a first stator plate and a second wall
130
of a second stator plate. The first wall
128
and second wall
130
cooperate in conjunction with the shroud
110
to define a flow pathway
132
for a fluid.
FIG. 12
schematically illustrates both a stator channel inlet
124
and stator channel outlet
126
. As illustrated, the channel defined by the first and second walls
128
,
130
, and shroud
110
, becomes narrower between the stator channel inlet
124
and the stator channel exit
126
. By reducing the stator channel cross-sectional area between the stator channel inlet
124
and the stator channel exit
126
, the desired pressure and flow conditions are maintained within the channel to compensate losses between the stator channel inlet
124
and stator channel exit
126
. In other words, the stator channel inlet
124
has a cross-sectional area larger than the stator channel exit
126
to compensate for losses that occur as the fluid
136
flows through the pathway
132
, and the impeller blades
118
, whereby decreasing the cross-sectional area maintains a desired pressure between the stator channel inlet
124
and the stator channel exit
126
.
The shroud
110
is shown having a circular cross-section as indicated at reference numeral
114
in FIG.
12
. Of course, the shroud
110
could comprise a plurality of various peripheral configurations to effect the flow pathway
132
. By having a circular shroud diameter
114
, separation of the fluid
136
from the shroud
110
is limited. This separation causes “verticality”, which results in turbulence and efficiency losses. Therefore, by providing a proper shroud periphery
114
, pumping efficiency is improved. Alternative shapes for the periphery
114
of the shroud
110
may be provided within the scope of the present invention. Specifically, the shroud periphery
114
may be configured in relation to the shape of the first and second walls
128
and
130
for defining the pathway
132
.
An interference fit is used for attaching the shroud
110
to the impeller blades
118
. The interference fit secures the shroud
110
to the impeller blades
118
by the shroud
110
applying compression forces upon the impeller blades
118
, wherein the impeller blades
118
oppose such compression forces by resisting such compression. To create the compression forces, the shroud
110
is selected having a shroud inner radius
112
at the flat portion
121
of the shroud
110
less than an impeller radius
116
. The radii
112
/
116
are schematically shown as identical in
FIG. 12
when, in fact, there is a pre-assembly difference therebetween causing the interference fit. The dimensional difference between the smaller shroud inner radius
112
and the larger impeller radius
116
is referred to as an amount of interference, wherein the amount of interference corresponds to a strength of interference between the shroud
110
and the impeller
120
, whereby at a required strength, the interference fit prevents axial movement of the shroud
110
in relation to the impeller blades
118
.
To determine the strength of interference required, a strength analysis is performed. The strength analysis includes a growth analysis to determine the growth of the impeller
120
and the shroud
110
during a predetermined theoretical range of operation for establishing the shroud inner radius
112
necessary to provide the amount of interference required irrespective of the growth of the impeller
120
and the shroud
110
. The theoretical range of operation is based upon predetermined parameters that affect the strength of interference. These parameters include impeller radius
116
, materials, temperature ranges, and speed of rotation.
During operation, depending on the speed of rotation and the type of material, the dimensions of the impeller
120
and the shroud
110
will vary. Of primary concern are the effects of the material growth due to ambient temperatures and temperatures produced by operation of the machine, which cause the expansion of the shroud
110
and the impeller
120
. Of further concern are the varying rates at which the shroud
110
may grow in relation to the impeller
120
. If the shroud inner radius
112
grows at a rate faster than the impeller radius
116
, the level of interference must be sufficiently maintained to prevent axial movement of the shroud
110
, or, alternatively, if the shroud inner radius
112
grows at a rate slower than the impeller radius
116
, the level of interference must be sufficiently maintained to prevent breakage of the shroud
110
or the impeller blades
118
and additionally to prevent axial movement of the shroud
110
in relation to the impeller blades
118
.
Therefore, the strength analysis determines the level of interference necessary to prevent axial movement of the shroud by analyzing the rate and quantity of material growth, such that the dimensional difference between the smaller shroud inner radius
112
and the larger impeller radius
116
are sufficiently in contrast that, irrespective of the growth of the impeller
120
and the shroud
110
, the shroud
110
is prevented from axial movement and breakage. As one ordinary in the skill will recognize, such strength analysis may be performed using finite element analysis computer software, such as ANSYS, available from Swanson Engineering of Canonsberg, Pa. Based on the strength analysis, the inner shroud radius
112
is selected.
The shroud
110
may then be attached to the impeller
120
by either forcing the shroud
110
upon the impeller blades
118
or, alternatively, by heating the shroud
120
for expansion, and cooling the shroud for shrinkage and engagement with the impeller blades
118
. Either method will produce the interference fit, however, if the dimensional difference between the shroud inner radius
112
and the impeller radius
116
is sufficiently large, forcing of the shroud
110
upon the impeller
120
may damage the impeller blades
118
, may not be a viable option.
The forcing of the shroud
110
upon the impeller
120
is accomplished by placing the shroud
110
within a fixture, not shown, containing the impeller
120
. The fixture centers the shroud
110
in relation to the impeller
120
and applies a minimal compression to force the shroud
110
over the impeller
120
. Additionally, the shroud inner radius
112
may be chamfered to facilitate the ease of forcing the shroud
110
upon the impeller
120
.
The heating and cooling the shroud
110
upon the impeller
120
is accomplished by first heating the shroud
110
, and then allowing the shroud
110
to cool upon the impeller
120
. Heating requires the shroud inner radius
112
to expand in dimension so that the shroud
110
may be easily placed upon the impeller blades
118
. Heating an aluminum shroud
110
to 400° F. will sufficiently increase the shroud inner radius
112
to a dimension greater than the impeller radius
116
to facilitate placing the shroud
110
in juxtaposition to the impeller
120
. The preferred temperature may vary based upon the strength analysis. While the shroud
110
is sufficiently heated, the shroud
110
is placed within the fixture, not shown, containing the impeller
120
, wherein the fixture centers the shroud
110
in relation to the impeller
120
and the shroud
110
is allowed to cool. Upon cooling, the shroud
110
forms the interference fit to the impeller
120
.
FIGS. 13-15
show a plan view, sectional view and perspective view, respectively of impeller
120
in accordance with the present invention.
FIGS. 16-18
show a plan view, sectional view and perspective view, respectively, of the shroud
110
attached to the impeller
120
in accordance with the present invention. As shown in
FIG. 17
, the shroud
110
includes a flat portion
121
at the interference fit, and a round portion
123
outwardly thereof to enhance flow.
As shown in
FIGS. 13 and 14
, the impeller
120
has radially extending impeller blades
125
, each having a distal end
127
. The distal ends
127
cooperate to form an outer impeller diameter (corresponding with the impeller radius
116
shown in FIG.
12
). The outer impeller diameter is less than the inner diameter of the shroud
110
(corresponding with the shroud inner radius
112
shown in FIG.
12
), formed by the flat portion
121
of the shroud
110
.
while embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
Claims
- 1. A method of combining an impeller and a shroud comprising:selecting a rotatable impeller element having impeller blades with radially extending distal ends defining a predetermined outer impeller diameter; selecting a shroud element having an inner diameter less than the outer impeller diameter; and attaching the shroud element to at least some of the radially extending distal ends of the impeller blades by forming an interference fit between the inner shroud diameter and the outer impeller diameter.
- 2. The method of claim 1, wherein said step of selecting a shroud element comprises:predetermining a theoretical operating condition in which the impeller and shroud elements will operate; performing strength analysis to determine the amount of interference fit required to effect the secure attachment of the shroud element to the ends of the impeller blades at the predetermined operating condition wherein the performance of the strength analysis includes, performing growth analysis to determine the growth of the impeller and shroud elements during theoretical operating condition, thereby to determine the shroud element thickness required to provide the required amount of interference fit irrespective of the growth of the impeller and shroud elements; and selecting the shroud element in accordance with such strength analysis.
- 3. The method of claim 2 further comprising selecting an outer shroud diameter configuration to discourage separation of the flow from the outer shroud diameter.
- 4. The method of claim 3, further comprising selecting a shroud having an at least partially circular cross-section to discourage separation caused by centrifugal forces of the fluid flow in the radial direction.
- 5. The method of claim 1, wherein said step of attaching the shroud comprises forcing the shroud over the impeller to produce the interference fit.
- 6. The method of claim 5, further comprising the use of a fixturing device to compressibly force the shroud upon the impeller.
- 7. The method of claim 5, wherein the shroud is chamfered at its inner diameter before the shroud is attached to further ease the forcing of the shroud upon the impeller blades.
- 8. The method of claim 1, wherein said step of attaching the shroud element comprises:heating the shroud element to increase the inner diameter of the shroud; placing the heated shroud element in a juxtaposed relation to the impeller blades; and cooling the shroud element to create an interference fit to combine the shroud element and the impeller element.
- 9. The method of claim 2, wherein the selection of the shroud element comprises the use of finite element analysis software to perform the strength analysis.
- 10. A method of manufacturing a regenerative flow machine having a shroud attached to an impeller, comprising:selecting a rotatable impeller element having impeller blades with radially extending distal ends defining a predetermined outer impeller diameter; selecting a shroud element having an inner diameter less than the outer impeller diameter; and attaching the shroud element to at least some of the radially extending distal ends of the impeller blades by an interference fit between the inner shroud diameter and the outer impeller diameter.
- 11. A method of manufacturing a gas turbine engine having a shroud attached to an impeller, comprising:selecting a rotatable impeller element having impeller blades with radially extending distal ends defining a predetermined outer impeller diameter; selecting a shroud element having an inner diameter less than the outer impeller diameter; and attaching the shroud element to at least some of the radially extending distal ends of the impeller blades by an interference fit between the inner shroud diameter and the outer impeller diameter.
- 12. An improved impeller comprising:a rotatable element having impeller blades with respective radially extending distal ends defining an outer impeller diameter; and a shroud surrounding the rotatable element and connected thereto by an interference fit with at least some of the distal ends.
- 13. A rotary machine including a helical flow compressor/turbine comprising:a housing; first and second stators positioned within the housing and having respective channels cooperating to define a substantially annular pathway within the housing; a shaft rotatably supported within the housing; a rotatable impeller element mounted for rotation with the shaft and having impeller blades substantially within the pathway, the impeller blades having respective radially extending distal ends defining an outer impeller diameter; a shroud surrounding the rotatable impeller element and connected thereto by an interference fit with at least some of the distal ends, the shroud in transverse cross-section having a flat portion at the interference fit and a rounded portion outwardly thereof, whereby the rounded portion cooperates with the channels of the first and second stators to define a flow pathway around the shroud.
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
5702229 |
Moss et al. |
Dec 1997 |
A |