Note: Descriptions are shown in the official language in which they were submitted.
CA 02092438 2001-07-06
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INTEGRATED CENTRIFUGAL PUMP AND MOTOR
This invention relates generally to centrifugal pumps and
more particularly to electrically driven centrifugal pumps
which require no shaft seals.
Centrifugal fluid pumps are well known in the hydraulic and
pneumatic fields. They commonly consist of a motor to drive
a shaft on which a fluid impeller is mounted. Generally,
the fluid inlet port, or suction port, feeds fluid to the
centre, or hub, of the impeller. A number of impeller vanes
generally project outward from the hub in spiral paths and
are supported between shrouds which, together with the
vanes, define pumping channels. The rotor is encased in a
housing which channels the working fluid from the inlet port
to the hub, or inducer, where it is inducted into the
pumping channels between the vanes and shrouds. The
centrifugal action of the impeller drives the working fluid
outward to a diffuser at the periphery of the impeller disc
where it enters a scroll shaped volute and, from there, is
channelled to the discharge port of t:he pump.
The motor shaft, which supports the impeller, requires
bearings which are sometimes lubr_Lcated by the working
fluid, but, in many cases, they require separate lubrication
due to incompatibility of the working fluid. In all cases,
seals are required to prevent leakage of the working fluid
around the impeller shaft where it enters the pump housing.
After some time in service, the bearings may deteriorate to
the point where they permit some radial displacement of the
rotating shaft. This causes accelerated wear and
deterioration of the shaft seal and results in leakage of
the working fluid from the pump housing.
CA 02092438 2001-O1-25
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FR-A-591,315 discloses a balancing device for centrifugal
pumps which comprises two balancing chambers formed on
either side of the c:h.eeks of an impeller and interconnected
by a duct. If e.g. a,s a result of inequalities in the plays
s existing on either side of the impeller, different pressures
become established in the balancing chambers. Fluid thus
flows through the duct to restore the equilibrium of the
pressures.
According to a broad aspect of the present
~o invention there is provided a centrifugal pump comprising a
housing having an internal chamber with inlet and discharge
ports. An impeller having a hub section is supported in the
chamber for rotation. about an axis to pump a working fluid.
The impeller has a central opening, first and second disk
~s shaped shrouds supported from the hub section, at least one
of the shrouds containing permanent magnets, and a plurality
of pumping channels defined by a plurality of impeller
blades projecting outwardly from the hub section in a common
plane between the first and second shrouds so as to rotate
zo in the common plane normal to the said axis . At least one
motor stator coil is provided for rotatably driving the
impeller. The stator coil is disposed adjacent the at least
one shroud containing ~he permanent magnets, so as to form a
gap between the stator coil and the shroud. The gap
z5 receives a small quantity of pumped working fluid. The
stator coil further r,as a central opening therein with the
working fluid passing through the impeller central opening
and through the stat=or coil central opening. Means is
provided for axial hydrodynamic balancing of the impeller.
3o This means comprise:; a ring disposed in the gap for
restricting the flow of the small quantity of pumped working
fluid. Means is provided for inducing flow of working fluid
toward the pumping channels from opposite directions. The
said means for inducing flow comprises an opening between
35 the hub section and each of the first and second shrouds and
CA 02092438 2001-O1-25
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an inducer in each of the openings. The inducer comprises a
pumping member which is separate from the impeller. A
recirculation passage is provided adjacent each inducer.
According to a still further broad aspect of the
s present invention there is provided a centrifugal pump which
comprises a housing having an internal chamber with inlet
and discharge ports. An impeller is supported in the
chamber for rotation. about an axis. The impeller has a hub
section. At least a first disc shaped shroud (is also
~o provided and contains permanent magnets. At least a first
stator coil is provided adjacent the permanent magnets. A
plurality of pumping channels are defined by a plura:Lity of
impeller blades projecting outwardly from the hub section
and fixed to a face of the shroud. Means is provided for
supplying fluid to the pumping channels and comprises at
least a first centra=L opening between the hub section and
the shroud. The centrifugal pump is characterised by at
least a first inducer in the opening and comprising a first
flow directing pumping member which is separate from the
zo impeller blades. A recirculation passage is provided
adjacent the or each inducer.
According to a still further broad aspect of the
present invention there is provided a centrifugal pump which
comprises a housing having an internal chamber connecting
Z5 inlet and discharge ports. A disc shaped impeller having
permanent magnets disposed therein is supported within the
chamber for rotation about an axis to pump a working fluid.
A motor stator coil is provided for rotatably driving the
impeller. The stator coil is disposed at a side of the
3o impeller so as to forrn a gap between the stator coil and the
impeller for receiving a small quantity of pump working
fluid. The centrifuga:L pump is characterised by a means for
axial hydrodynamic balancing of the impeller and comprising
a ring disposed in the gap for restricting flow of the small
35 quantity of pumped working fluid therethrough.
CA 02092438 2001-O1-25
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For a better understanding of the invention and to
show how the same may be carried into effect, reference will
now be made, by way of example, to the accompanying
drawings, in which:-
Figure 1 i~: a schematic sectional elevation view
illustrating one embodiment of a centrifugal pump;
Figure 2 i~; a schematic sectional elevation view
of another embodiment of the pump; and
Figure 3 is a fragmentary view along line 3-3 of
~o the pump shown in Figure 1.
WO 92/06301 PCT/US91/07122
3
DETAILED DESCRIPTION
Fig. 1 is a schematic cross sectional view of one
embodiment of the pump of the present invention, which is
seen to be laterally symmetrical about the vertical center
plane represented by the centerline of Fig. 1. The housing
has an inlet port il and a discharge port 12 which are
connected by means of inducer assembly 18, impeller shrouds
15, rotating vaneless diffuser 24, and volute 13. The pump
fluid enters at the inlet port il; divides and passes into
the two sides of the inducer assembly 18; passes between the
two impeller shrouds 15 through pumping channels 55 (shown
in Fig. 3) which are defined by the spaces between
neighboring impeller blades 21 and the impeller shrouds 15,
between which the impeller blades 21 are disposed; passes
through the rotating vaneless diffuser 24; then passes
through the volute 13 and into discharge port 12. Between
diffuser 24 and volute 13 a small amount of the high
pressure fluid feeds back through axial thrust balance
passages 45. These narrow passages provide the gap
necessary for rotation of the rotor shrouds 15 between the
stators 14 and, by admission of the feedback fluid, provide
a hydrodynamic balance to counteract any axial thrusts of
the rotor 15 so that it remains centered between stators 14.
Axial thrust balancing rings 16 are provided in the balance
passage 45 either on the surface of the stator can 17 or on
a projection of housing 10. By narrowing the axial gap
between the impeller shrouds 15 and ~.tator cans 17 or
housing 10, these rings cause an increase of fluid pressure
in the balance passage 45 which enhances the axial thrust
balance performance.
The alternative provided for placement of the axial
' thrust balancing rings 16 is required because, in some
cases, stators 14 will not be canned or encapsulated. In
such cases, it is necessary to place the axial thrust
balancing rings 16 on projections of housing 10. Each half
WO 92/06301 PCT/US91/07122
2~9~~3~
4
of housing 10 has a toroidal recess 33 in which a stator 14
is secured. In addition, recirculation passages 20 are
provided to assure smooth inducer action at off-design flow
rates.
The rotor assembly which includes inducer assembly 18,
shrouds 15, impeller blades 21, and rotating diffuser 24 is
supported on journals provided on the outside of the tubular
axial extensions of shrouds 15 in radial magnetic bearings
35 and auxiliary bearings 40. During operation, the rotor
is supported by the radial magnetic bearings 35 which have a
large enough clearance to provide non-contact bearing
support to the rotor. Should the magnetic bearings 35 fail
to support the rotor, auxiliary bearings 40 are provided for
the ensuing emergency rundown of the rotor only, and they
have a smaller clearance than do magnetic bearings 35.
Impeller shrouds 15 each contain a peripheral array of
permanent magnets required for a rotor in a brushless DC
motor when used in conjunction with stators 14 containing
the windings and electrical connections required for
operation as a motor. Because impeller shrouds 15 contain
permanent magnets, and because shrouds 15 are supported in
radial magnetic bearings 35 and auxiliary bearings 40, there
is no need for any shaft to penetrate the housing 10 and,
thus, no need for rotary shaft seals which can cause wear of
the shaft and will eventually leak.
Fig. 2 illustrates another embodiment of the pump of
the present invention. In this case the housing 10 is
composed of several sections, and it has two inlets 11.
Otherwise, in all other respects, the pumps are functionally
identical. For this reason, numbering of the various
components has been retained consistent with that used in
Fig. 1.
Fig. 3 shows a fragmentary schematic sectional view of
the rotor and housing along line 3-3 of Fig. 1. Vanes 21
are attached to shroud 15. Inducer assembly 18 feeds fluid
WO 92/06301 PCT/US91/07122
to the impeller blades which pump it radially outward
through pumping channels 55 defined by blades 21 and shrouds
15. Diffuser 24 is defined by that space between the two
shrouds 15 radially outside that which is occupied by blades
21. Pressurized fluid from diffuser 24 is carried away
through volute 13.
The particular design parameters for a given pumping
application are determined by pressure and volume
requirements, space constraints, working fluid properties,
and desired orientation of inlet and discharge ports. These
are the considerations that determine the diameter of the
impeller shrouds 15, the spacing between the shrouds and
consequently the width of the impeller blades 21, the size
of diffuser 24 if needed, the size of inducer assembly 18,
and the size and shape of the pump housing 10 and
recirculation passages 20 which are provided to assure
smooth inducer action at off-design flow rates. Stators 14
and impeller shrouds 15 are matched according to pumping
power requirements. Stators 14 may or may not be
encapsulated in cans 17, depending upon whether the working
fluid is compatible with the stators.
This invention provides an integrated centrifugal pump
and motor having the advantages of compactness, the ability
to operate electronically at variable speeds, a shaftless
rotor which requires no seals, non-contact radial bearing
supports during operation, and hydrodynamic axial thrust
balance for the rotor. These advantages are obtained when
pumping either compressible or incompressible fluids.
