Information
-
Patent Grant
-
6514036
-
Patent Number
6,514,036
-
Date Filed
Friday, April 27, 200123 years ago
-
Date Issued
Tuesday, February 4, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Look; Edward K.
- McCoy; Kimya N
Agents
- Harness, Dickey & Pierce, P.L.C.
-
CPC
-
US Classifications
Field of Search
US
- 415 98
- 415 119
- 415 206
- 415 102
- 415 101
- 416 175
- 416 203
- 015 326
-
International Classifications
-
Abstract
A debris blower with a radial flow fan having an impeller that includes a set of impeller blades that are spaced about a rotary axis of the impeller in a predetermined manner such that at least two spacing angles are used to space the impeller blades circumferentially apart from one another. The use of a plurality of spacing angles operates to distribute the noise that is generated by the rotating impeller blades over several tones or frequencies.
Description
FIELD OF THE INVENTION
The present invention generally relates to radial flow fans and more particularly to a debris blower including a radial flow fan having an impeller with a noise reducing blade configuration.
BACKGROUND OF THE INVENTION
Debris blowers are known in which an impeller or a fan driven by a motor creates an air stream which is directed into a duct. The air stream discharged from the open end of the duct is employed to blow debris off walks, driveways and lawns. Known higher performance blowers employ a radial flow fan in order to efficiently generate the pressure and volumetric flow rate required for the application. These devices tend to be relatively noisy such that their use is often unpleasant for the user and those in the vicinity of the blower.
The scale of the impeller, the practical speeds at which it can be driven, and a practical number of blades results in blade passing frequencies that create tonal noise emission. Tonal emission at the blade passing frequency typically falls within the frequency range over which the human ear is sensitive and creates an unpleasant sound quality. Further, as the impeller blades of these devices are typically spaced apart evenly around the circumference of the impeller, the noise emission contains one or more discrete tones at frequencies related to the blade passing rate. It is this concentration of noise at one or more particular frequencies, rather than the overall amplitude of the noise, that most people find unpleasant.
Given the design criteria of modern high performance debris blowers, along with issues relating to its overall size, weight and cost, changes to the size of the impeller, its rotational speed and/or the number of impeller blades to change the frequency of the noise that is generated by the passing impeller blades to a frequency that is outside the sensitive range of human hearing have not been practicable.
It is therefore an object of the present invention to provide a radial flow fan having an impeller with a blade configuration that spreads the blade passing noise out over several frequencies to improve the quality of the noise that is generated during the operation of the radial flow fan.
SUMMARY OF THE INVENTION
In one preferred form, the present invention provides a radial flow fan having a housing having at least one inlet, an outlet and an impeller cavity in fluid connection with the inlet and the outlet, and an impeller. The impeller is rotatably supported in the impeller cavity on a rotary axis and includes an annular flange member and a plurality of impeller blades that are fixedly coupled to the annular flange member such that each of the impeller blades is adjacent another of the impeller blades in a predetermined circumferential direction. Each adjacent pair of the impeller blades defines a spacing angle. The impeller is configured such that a first predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a first predetermined spacing angle and a second predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a second predetermined spacing angle that is not equal to the first predetermined spacing angle. The plurality of first impeller blades are configured to intake a compressible fluid in a first direction generally parallel the rotary axis and to expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity. The use of a plurality of spacing angles operates to distribute the noise that is generated by the rotating impeller blades over several tones or frequencies.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein:
FIG. 1
is a side view of a blower constructed in accordance with the teachings of the present invention;
FIG. 2
is a sectional view of the blower of
FIG. 1
taken along its longitudinal axis;
FIG. 3
is an end view of a portion of the blower of
FIG. 1
, illustrating the set of first impeller blades in greater detail;
FIG. 4
is an end view of the impeller illustrating the set of second impeller blades in greater detail;
FIG. 5
is a perspective view of the impeller illustrating the set of first impeller blades; and
FIG. 6
is a perspective view of the impeller illustrating the set of second impeller blades.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to
FIGS. 1 and 2
of the drawings, a blower constructed in accordance with the teachings of the present invention is generally indicated by reference numeral
10
. The blower
10
is shown to include a power source
12
, a switch assembly
14
for selectively controlling the power source, a housing
16
, an impeller
18
and a discharge tube assembly
20
. In the particular embodiment illustrated, the power source
12
is illustrated to include a motor assembly
30
having an electric motor
32
with a pair of terminals
34
and an output shaft
36
. The motor assembly
30
and switch assembly
14
are conventional in their construction and operation and need not be discussed in significant detail. Briefly, the switch assembly
14
is coupled to a source of electric power (e.g., via a power cord
40
) and via the terminals
34
, selectively provides the motor
32
with electricity in a predetermined manner that is related to the amount by which a trigger button
46
on the switch assembly
14
is depressed.
The housing
16
is illustrated to include a pair of housing shells
50
that collectively define a motor mounting portion
52
, a switch mounting portion
54
and a volute
58
having an impeller cavity
60
, a primary inlet
62
, a secondary inlet
64
and an outlet
68
. The motor and switch mounting portions
52
and
54
are conventional in their construction and operation, being employed to fixedly couple the motor assembly
30
and the switch assembly
14
, respectively, within the housing
16
. When the motor assembly
30
is coupled to the housing
16
by the motor mounting portion
52
, the distal end of the output shaft
36
extends rearwardly into the impeller cavity
60
.
The impeller cavity
60
extends radially around the output shaft
36
and is substantially enveloped on its forward and rearward sides by a pair of annular endwalls
70
and
72
, respectively, into which the secondary and primary inlets
62
and
64
, respectively, are formed. A plurality of vent apertures
76
that are skewed to the rotary axis
80
of the output shaft
36
are formed through the housing
16
forwardly of the endwall
70
. A plurality of circumferentially extending inlet apertures
86
are spaced around the housing
16
rearwardly of the endwall
72
. The circumference of the portion of the housing
16
into which the inlet apertures
86
are formed is illustrated to be larger than the diameter of the primary inlet
62
. The outlet
68
intersects the impeller cavity
60
generally tangent to the outer diameter of the impeller cavity
60
in a manner that is conventionally known. However, the outlet
68
turns forwardly after this intersection and extends along an axis that is offset both vertically and horizontally from the rotary axis
80
of the output shaft
36
. The outlet
68
terminates at a coupling portion
90
that is configured to releasably engage a mating coupling portion
92
on the proximal end
94
of the discharge tube assembly
20
.
With reference to
FIGS. 2 through 6
, the impeller
18
is illustrated to include a mounting hub
100
, a flange member
102
, a set of first impeller blades
104
and a set of second impeller blades
106
. The mounting hub
100
is generally cylindrical and includes a mounting aperture
110
, which is sized to engage the distal end of the output shaft
36
in a press-fit manner to thereby couple the impeller
18
to the motor assembly
30
for rotation about the rotary axis
80
. Those skilled in the art will readily understand that although press-fitting is employed to fix the impeller
18
for rotation with the output shaft
36
, any appropriate coupling means may be utilized for this purpose. The flange member
102
is coupled to the mounting hub
100
and extends radially outwardly therefrom in a continuous manner to thereby completely segregate the sets of first and second impeller blades
104
and
106
from one another.
During the operation of the blower
10
, the impeller
18
rotates within the impeller cavity
60
. Rotation of the set of first impeller blades
104
imparts momentum to the air that is disposed between each adjacent pair of first impeller blades
104
, slinging the air radially outwardly toward the outlet
68
. The air exiting the outlet
68
as a result of the momentum imparted by the set of first impeller blades
104
creates a negative pressure differential that generates a primary air flow
120
that enters the housing
16
through the inlet apertures
86
and is directed into the set of first impeller blades
104
by the primary inlet
62
in a direction generally parallel the rotary axis
80
.
Similarly, rotation of the set of second impeller blades
106
imparts momentum to the air that is disposed between each adjacent pair of second impeller blades
106
, slinging the air radially outwardly toward the outlet
68
. The air exiting the outlet
68
as a result of the momentum imparted by the set of second impeller blades
106
creates a negative pressure differential that generates a secondary air flow
122
that enters the housing
16
through the vent apertures
76
. The housing
16
is constructed such that the motor
32
rejects heat to the secondary air flow
122
before it travels through the secondary inlet
64
. The secondary inlet
64
directs the secondary flow
122
into the set of second impeller blades
106
in a direction generally parallel the rotary axis
80
and opposite the primary air flow
120
.
The primary and secondary air flows
120
and
122
combine in the outlet
68
and are discharged through the coupling portion
90
into the discharge tube assembly
20
. In the example provided, the height of the first impeller blades
104
is substantially larger than that of the second impeller blades
106
and as such, the mass flow rate of the primary air flow
120
will be substantially larger than the mass flow rate of the secondary air flow
122
. As the flange member
102
is continuous, the primary and secondary flows
120
and
122
cannot travel in an axial direction beyond the flange member
102
until they have been slung radially outwardly of the impeller
18
.
The set of first impeller blades
104
is fixedly coupled to a first side
150
of the flange member
102
such that each pair of the first impeller blades
104
(e.g., first impeller blades
104
a
and
104
b
) is separated by a predetermined spacing angle
152
, wherein one of the pair of first impeller blades
104
(e.g., first impeller blade
104
b
) is spaced apart from the other one of the pair of first impeller blades
104
(e.g., first impeller blade
104
a
) in a predetermined circumferential direction by the spacing angle
152
. The set of first impeller blades
104
are spaced about the flange member
102
such that spacing angles
152
having at least two different magnitudes are employed to space the first impeller blades
104
apart. Preferably, the set of first impeller blades
104
are spaced apart with a spacing angles
152
having a multiplicity of magnitudes, wherein the spacing angles
152
are distributed in a predetermined pattern that is repeated around the circumference of the impeller
18
.
Similarly, the set of second impeller blades
106
is fixedly coupled to a second side
160
of the flange member
102
such that each pair of the second impeller blades
106
(e.g., second impeller blades
106
a
and
106
b
) is separated by a predetermined spacing angle
162
, wherein one of the pair of second impeller blades
106
(e.g., second impeller blade
106
b
) is spaced apart from the other one of the pair of second impeller blades
106
(e.g., second impeller blade
106
a
) in a predetermined circumferential direction by the spacing angle
162
. The set of second impeller blades
106
are also spaced about the flange member
102
such that spacing angles
162
having at least two different magnitudes are employed to space the second impeller blades
106
apart. As with the set of first impeller blades
104
, the set of second impeller blades
106
are preferably spaced apart with spacing angles
162
having a multiplicity of magnitudes, wherein the spacing angles
162
are distributed in a predetermined pattern that is repeated around the circumference of the impeller
18
. Also preferably, the magnitudes and pattern of spacing angles
162
for the set of second impeller blades
106
is different from the magnitudes and pattern of the spacing angles
152
for the set of first impeller blades
104
.
In the particular embodiment illustrated, the pattern of spacing angles
152
that is employed for the set of first impeller blades
104
is configured such that a first one of the first impeller blades
104
(e.g., first impeller blade
104
b
) is adjacent a first one of the other first impeller blades (e.g., first impeller blade
104
a
) and cooperates to define a first area
170
on the flange member
102
therebetween, and each of the first impeller blades
104
(e.g., first impeller blade
104
b
) is also adjacent a second one of the other first impeller blades (e.g., first impeller blade
104
c
) and cooperates to define a second area
172
on the flange member
102
therebetween. The spacing of the first impeller blades
104
is such that none of the first and second areas
170
and
172
that are adjacent any one of the first impeller blades
104
is equal in magnitude.
Each of the first impeller blades
104
is shown to begin at an inward point
174
and terminate at an outward point
176
. Each of the first impeller blades
104
(e.g., first impeller blade
104
b
) is configured such that its inward point
174
is radially inward of the outward point
176
of the first one of the other first impeller blades
104
(e.g., first impeller blade
104
a
) and its outward point
176
is radially outward of the inward point
174
of the second one of the other first impeller blades
104
(e.g., first impeller blade
104
c
). Accordingly, a first straight line passes through the mounting aperture
110
through the inward point
174
of the first impeller blade
104
b
and the outward point
176
of the first impeller blade
104
a
and a second straight line passes through the mounting aperture
110
through the inward point
174
of the first impeller blade
104
c
and the outward point
176
of the first impeller blade
104
b.
Each first impeller blade
104
is arcuately shaped from its inward point
174
to its outward point
176
. Each first impeller blade
104
tapers outwardly away from the flange member
102
from its inward point
174
to an intermediate point
178
between the inward and outward points
174
and
176
.
Similarly, the pattern of spacing angles
162
that is employed for the set of second impeller blades
106
is configured such that each of the second impeller blades
106
(e.g., second impeller blade
106
b
) is adjacent a first one of the other second impeller blades (e.g., second impeller blade
106
a
) and cooperates to define a third area
180
on the flange member
102
therebetween, and each of the second impeller blades
106
(e.g., second impeller blade
106
b
) is also adjacent a second one of the other second impeller blades (e.g., second impeller blade
106
c
) and cooperates to define a fourth area
182
on the flange member
102
therebetween. The spacing of the second impeller blades
106
is such that none of the third and fourth areas
180
and
182
that are adjacent any one of the second impeller blades
106
is equal in magnitude.
Each of the second impeller blades
106
begins at an inward point
184
and terminates at an outward point
186
. Each of the second impeller blades
106
(e.g., second impeller blade
106
b
) is configured such that its outward point
186
is radially outward of the inward point
184
of the first one of the other second impeller blades
106
(e.g., second impeller blade
106
a
) and its inward point
184
is radially inward of the outward point
186
of the second one of the other second impeller blades
106
(e.g., second impeller blade
106
c
). Each second impeller blade
106
is arcuately shaped from its inward point
184
to its outward point
186
. Accordingly, a first straight line passes through the mounting aperture
110
through the inward point
184
of the first impeller blade
106
b
and the outward point
186
of the first impeller blade
106
c
and a second straight line passes through the mounting aperture
110
through the inward point
184
of the first impeller blade
106
a
and the outward point
186
of the first impeller blade
106
b.
Each second impeller blade
106
tapers outwardly away from the flange member
102
from its inward point
184
to an intermediate point
188
between the inward and outward points
184
and
186
.
Preferably, the spacing between any adjacent pair of impeller blades is not equal to any other spacing between an adjacent pair of any of the other first and second impeller blades
104
and
106
to thereby distribute the noise energy over a maximum number of frequencies. Construction in this manner, however, is extremely difficult, particularly where the impeller
18
is formed in a molding process, due to the unsymmetrical distribution of material in the impeller
18
. The unsymmetrical distribution of material tends to facilitate distortion in the molded impeller
18
as it cools, as well as offsets its rotational center of gravity about its axis of rotation so that it vibrates when it is rotated.
In view of these difficulties, the set of first impeller blades
104
are instead divided into a plurality of identically configured first blade groups
200
, wherein each of the first blade groups
200
includes an identical quantity of the first impeller blades
104
which are spaced apart in a predetermined first blade spacing pattern. In the example provided, each of the first blade groups
200
includes a total of four (4) of the first impeller blades
104
a,
104
b,
104
c
and
104
d,
with the first impeller blade
104
a
being spaced apart from predetermined reference point (e.g. the first impeller blade
104
d
in another first blade group
200
) by an angle of 57°, the first impeller blades
104
a
and
104
b
being spaced apart with a spacing angle
152
of 41°, the first impeller blades
104
b
and
104
c
being spaced apart with a spacing angle
152
of 49° and the first impeller blades
104
c
and
104
d
being spaced apart with a spacing angle
152
of 33°. The first blade groups
200
are fixed to the first side
150
of the flange member
102
such that they are offset from one another by a predetermined angular spacing (e.g., 57°).
Similarly, the set of second impeller blades
106
are divided into a plurality of identically configured second blade groups
220
, wherein each of the second blade groups
220
includes an identical quantity of the second impeller blades
106
which are spaced apart in a predetermined second blade spacing pattern. In the example provided, each of the second blade groups
220
includes a total of three (3) of the second impeller blades
106
a,
106
b
and
106
c,
with the second impeller blade
106
a
being spaced apart from predetermined reference point (e.g. the second impeller blade
106
c
in another second blade group
220
) by an angle of 40°, the second impeller blades
106
a
and
106
b
being spaced apart with a spacing angle
162
of 32° and the second impeller blades
106
b
and
106
c
being spaced apart with a spacing angle
162
of 48°. The second blade groups
220
are fixed to the second side
170
of the flange member
102
such that they are offset from one another by a predetermined angular spacing (e.g., 40°).
While noise attenuation is primarily achieved through the configuration of the impeller
18
, the geometry of the housing
16
is also employed to aid in the attenuation of the noise that is generated during the operation of the blower
10
. In this regard, noise that results from the rotation of the impeller
18
is not discharged in a direct or straight-line manner from the housing
16
but rather is reflected off several various interior surfaces within the housing
16
as shown in FIG.
2
. For example, noise
250
that is directed rearwardly from the impeller
18
is reflected off the rearward wall
252
before it is reflected outwardly through the inlet apertures
86
. Similarly, noise
250
that is directed forwardly from the impeller
18
is reflected off the walls
254
of the outlet
68
before it is discharged through the outlet
68
. The reflecting of noise
250
off the various interior surfaces of the housing
16
permits the housing
16
to absorb some of the energy of the noise
250
to thereby attenuate the level of noise
250
that is transmitted out of the housing
16
.
While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.
Claims
- 1. A radial flow fan comprising:a housing having at least one inlet, an outlet and an impeller cavity in fluid connection with the inlet and the outlet; and an impeller rotatably supported in the impeller cavity on a rotary axis, the impeller having an annular flange member and a plurality of impeller blades fixedly coupled to the annular flange member such that each of the impeller blades is adjacent another of the impeller blades in a predetermined circumferential direction, each adjacent pair of impeller blades defining a spacing angle, the impeller being configured such that a first predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a first predetermined angle and a second predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a second predetermined angle that is not equal to the first predetermined angle, the plurality of impeller blades being segregated into a plurality of identically configured first blade groups, each of the first blade groups having an equal number of impeller blades, the impeller blades within one of the first blade groups being spaced apart from one another with a predetermined pattern of spacing angles including at least one of the first predetermined angle and the second predetermined angle; wherein the plurality of impeller blades are configured to intake a compressible fluid in a first direction generally parallel the rotary axis and expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity.
- 2. The portable debris blower of claim 1, wherein a spacing angle between a last impeller blades in a first one of the impeller blade groups and a first one of the impeller blades in a next one of the impeller blade groups is not equal to a spacing angle between each adjacent pair of impeller blades in the first one of the impeller blade groups.
- 3. The portable debris blower of claim 2, wherein the predetermined pattern of spacing angles includes a plurality of non-equal spacing angles.
- 4. The radial flow fan of claim 1, wherein the predetermined pattern of spacing angles includes a plurality of non-equal spacing angles.
- 5. The radial flow fan of claim 1, further comprising a plurality of second impeller blades, the second impeller blades being fixedly coupled to the annular flange member such that each of the second impeller blades is adjacent another of the second impeller blades in a predetermined circumferential direction, each adjacent pair of second impeller blades defining a second spacing angle, the impeller being configured such that a first predetermined quantity of the second impeller blades are spaced apart from an associated adjacent second impeller blade with a third predetermined angle and a second predetermined quantity of the second impeller blades are spaced apart from an associated adjacent second impeller blade with a fourth predetermined angle that is not equal to the third predetermined angle;wherein the plurality of second impeller blades are configured to intake a compressible fluid in a second direction generally parallel the rotary axis and expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity.
- 6. The radial flow fan of claim 5, wherein the plurality of second impeller blades are segregated into a plurality of identically configured second blade groups, each of the second blade groups having an equal number of the second impeller blades, the second impeller blades within one of the second blade groups being spaced apart from one another with a predetermined second pattern of spacing angles including at least one of the third predetermined angle and the fourth predetermined angle.
- 7. The portable debris blower of claim 6, wherein a spacing angle between a last impeller blades in a first one of the second impeller blade groups and a first one of the impeller blades in a next one of the second impeller blade groups is not equal to a spacing angle between each adjacent pair of the second impeller blades in the first one of the second impeller blade groups.
- 8. The portable debris blower of claim 7, wherein the predetermined pattern of spacing angles includes a plurality of non-equal spacing angles.
- 9. The portable debris blower of claim 6, wherein the predetermined pattern of spacing angles includes a plurality of non-equal spacing angles.
- 10. The portable debris blower of claim 6, wherein each of the second impeller blades begins at an inward point and terminates at an outward point, each of the second impeller blades being configured such that its inward point is radially inward of the outward point of the first one of the outer second impeller blades and its outward point is radially outward of the inward point of the second one of the other second impeller blades.
- 11. The portable debris blower of claim 10, wherein each of the second impeller blades is arcuately shaped from the inward point to the outward point.
- 12. The portable debris blower of claim 10, wherein each of the second impeller blades tapers outwardly away from the flange member from the inward point to an intermediate point between the inward and outward points.
- 13. The portable debris blower of claim 6, wherein the predetermined number of first blade groups is not, equal to the predetermined number of second blade groups.
- 14. The portable debris blower of claim 13, wherein a quantity of the first impeller blades that form one of the first blade groups is not equal to a quantity of the second impeller blades that form one of the second blade groups.
- 15. The portable debris blower of claim 1, wherein each of the impeller blades begins at an inward point and terminates at an outward point, each of the impeller blades being configured such that its inward point is radially inward of the outward point of the first one of the other impeller blades and its outward point is radially outward of the inward point of the second one of the other impeller blades.
- 16. The portable debris blower of claim 15, wherein each of the impeller blades is arcuately shaped from the inward point to the outward point.
- 17. The portable debris blower of claim 15, wherein each of the impeller blades tapers outwardly away from the flange member from the inward point to an intermediate point between the inward and outward points.
- 18. A radial flow fan comprising:a housing having at least one inlet, an outlet and an impeller cavity in fluid connection with the inlet and the outlet; and an impeller rotatably supported in the impeller cavity on a rotary axis, the impeller including: an annular flange member; a plurality of first impeller blades fixedly coupled to the annular flange member such that each of the first impeller blades is adjacent another of the first impeller blades in a predetermined circumferential direction, each adjacent pair of first impeller blades defining a first spacing angle, the impeller being configured such that a first predetermined quantity of the first impeller blades are spaced apart from an associated adjacent first impeller blade with a first predetermined angle and a second predetermined quantity of the first impeller blades are spaced apart from an associated adjacent first impeller blade with a second predetermined angle that is not equal to the first predetermined angle, the plurality of first impeller blades being segregated into a plurality of identically configured first blade groups, each of the first blade groups having an equal number of first impeller blades, the first impeller blades within one of the first blade groups being spaced apart from one another with a predetermined pattern of spacing angles including at least one of the first predetermined angle and the second predetermined angle; a plurality of second impeller blades, the second impeller blades being fixedly coupled to the annular flange member such that each of the second impeller blades is adjacent another of the second impeller blades in a predetermined circumferential direction, each adjacent pair of second impeller blades defining a second spacing angle, the impeller being configured such that a first predetermined quantity of the second impeller blades are spaced apart from an associated adjacent second impeller blade with a third predetermined angle and a second predetermined quantity of the second impeller blades are spaced apart from an associated adjacent second impeller blade with a fourth predetermined angle that is not equal to the third predetermined angle, the plurality of second impeller blades being segregated into a plurality of identically configured second blade groups, each of the second blade groups having an equal number of the second impeller blades, the second impeller blades within one of the second blade groups being spaced apart from one another with a predetermined second pattern of spacing angles including at least one of the third predetermined angle and the fourth predetermined angle; wherein the plurality of first impeller blades are configured to intake a compressible fluid in a first direction generally parallel the rotary axis and expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity; and wherein the plurality of second impeller blades are configured to intake a compressible fluid in a second direction generally parallel the rotary axis and expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity.
US Referenced Citations (6)