U.S. patent application number 12/699754 was filed with the patent office on 2010-06-03 for rotary blood pump.
Invention is credited to David M. Lancisi, Richard K. Wampler.
Application Number | 20100135832 12/699754 |
Document ID | / |
Family ID | 34375465 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100135832 |
Kind Code |
A1 |
Wampler; Richard K. ; et
al. |
June 3, 2010 |
Rotary Blood Pump
Abstract
Various "contactless" bearing mechanisms including hydrodynamic,
hydrostatic, and magnetic bearings are provided for a rotary pump
as alternatives to mechanical contact bearings. These design
features may be combined. In one embodiment, a pump housing has a
spindle extending from a wall of the pump housing into a pumping
chamber defined by the pump housing. The spindle has a stepped
portion adjacent the wall. In one embodiment, the stepped portion
is defined by a change in spindle diameter. The lack of mechanical
contact bearings enables longer life pump operation and less damage
to working fluids such as blood.
Inventors: |
Wampler; Richard K.;
(Loomis, CA) ; Lancisi; David M.; (Folsom,
CA) |
Correspondence
Address: |
INSKEEP INTELLECTUAL PROPERTY GROUP, INC
2281 W. 190TH STREET, SUITE 200
TORRANCE
CA
90504
US
|
Family ID: |
34375465 |
Appl. No.: |
12/699754 |
Filed: |
February 3, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10937109 |
Sep 9, 2004 |
7682301 |
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12699754 |
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60504233 |
Sep 18, 2003 |
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Current U.S.
Class: |
417/423.1 |
Current CPC
Class: |
F16C 2316/18 20130101;
F04D 13/06 20130101; F04D 29/047 20130101; A61M 60/205 20210101;
A61M 60/824 20210101; A61M 60/82 20210101; F16C 32/044 20130101;
F04D 29/043 20130101; F04D 29/22 20130101; A61M 60/419 20210101;
Y10S 415/90 20130101; F04D 29/628 20130101; A61M 60/422 20210101;
A61M 60/818 20210101; F04D 29/0413 20130101; F04D 29/426 20130101;
F04D 13/0666 20130101; A61M 60/148 20210101; F04D 1/00 20130101;
F04D 29/0473 20130101; F04D 29/048 20130101 |
Class at
Publication: |
417/423.1 |
International
Class: |
F04B 17/00 20060101
F04B017/00 |
Claims
1. A pump apparatus, comprising: a rotor comprising paddles located
at a periphery of the rotor to generate hydrostatic thrust forces,
the paddles distinct from any impeller blades.
2. The apparatus of claim 1 wherein the rotor further comprises a
grooved bore for generating hydrostatic thrust forces during
rotation.
3. The apparatus of claim 1 further comprising a plurality of drive
magnets disposed within a non-bladed portion of the rotor.
4. A pump apparatus, comprising: a rotor having grooves located at
a periphery of the rotor, the grooves establishing hydrostatic
thrust forces during rotation of the rotor.
5. The apparatus of claim 4 wherein the rotor further comprises a
grooved bore for generating hydrostatic thrust forces during
rotation.
6. The apparatus of claim 4 wherein the rotor has a surface
geometry suitable for supporting a hydrodynamic bearing.
7. The apparatus of claim 6 wherein the surface geometry comprises
a plurality of spiral grooves.
8. The apparatus of claim 6 wherein the surface geometry comprises
a herringbone groove pattern.
9. The apparatus of claim 18 further comprising a plurality of
drive magnets disposed within a non-bladed portion of the
rotor.
10. A pump apparatus comprising: a rotor having a grooved bore
structured for generating hydrostatic thrust forces during
rotation.
11. The apparatus of claim 10 further comprising a plurality of
drive magnets disposed within a non-bladed portion of the rotor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/504,233 of Wampler, et al. filed Sep. 18,
2003.
FIELD OF THE INVENTION
[0002] This invention relates to the field of rotary pumps. In
particular, this invention is drawn to bearings for various rotor
and impeller architectures.
BACKGROUND OF THE INVENTION
[0003] Typical rotary pumps utilize an impeller wherein the
movement of the impeller is constrained in five degrees of freedom
(two angular, three translational) by mechanical contact bearings.
Some working fluids may be damaged by the mechanical contact
bearings. Blood pumped through pumps with contact bearings can
experience hemolysis, i.e., damage to blood cells. In general, a
hydraulically efficient and power efficient pump that can handle
delicate working fluids such as blood is desirable for some
applications.
[0004] U.S. Pat. No. 6,234,772 B1 of Wampler, et al., ("Wampler")
describes a centrifugal blood pump having a repulsive radial
magnetic bearing and an axial hydrodynamic bearing. U.S. Pat. No.
6,250,880 B1 of Woodard, et al. ("Woodard") describes a centrifugal
blood pump with an impeller supported exclusively by hydrodynamic
forces.
[0005] Both blood pumps are based on an axial flux gap motor
design. The pump impeller carries the motor drive magnets thus
serving as a motor rotor. In both cases, the drive magnets are
disposed within the blades of the impeller. Drive windings reside
outside the pump chamber but within the pump housing that serves as
the motor stator. Integration of the motor and pump enables the
elimination of drive shafts and seals for the pumps. The
pump/motors include a back iron to increase the magnetic flux for
driving the impeller.
[0006] Both blood pumps suffer from hydraulic inefficiencies due at
least in part to the large, unconventional blade geometry required
for disposing the magnets within the impeller blades.
[0007] The natural attraction between the magnets carried by the
impeller and the back iron creates significant axial forces that
must be overcome in order for the pump to work efficiently.
Hydrodynamic bearings can damage blood cells as a result of shear
forces related to the load carried by the hydrodynamic bearings
despite the lack of contact between the impeller and the pump
housing. Thus exclusive reliance on hydrodynamic bearings may be
harmful to the blood.
SUMMARY OF THE INVENTION
[0008] In view of limitations of known systems and methods, various
"contactless" bearing mechanisms are provided for a rotary pump as
alternatives to mechanical contact bearings. Various rotor and
housing design features are provided to achieve hydrodynamic,
hydrostatic, or magnetic bearings. These design features may be
combined. The lack of mechanical contact bearings enables longer
life pump operation and less damage to working fluids such as
blood.
[0009] In one embodiment, a pump includes a pump housing defining a
pumping chamber. The pump housing has a spindle extending into the
pumping chamber. The spindle further comprises an upper spindle
magnet and a lower spindle magnet. A rotor configured to rotate
about the spindle has an upper rotor magnet and a lower rotor
magnet. The upper spindle and rotor magnets are arranged to repel
each other. The lower spindle and rotor magnets are arranged to
repel each other.
[0010] In one embodiment, the pump includes a hydrostatic thrust
bearing. The pump housing has a spindle extending from a wall of
the pump housing into the pumping chamber defined by the pump
housing. The spindle has a stepped portion adjacent the wall. In
one embodiment, the stepped portion is defined by a change in
spindle diameter.
[0011] In various embodiments, the rotor includes either paddles or
grooves disposed about the periphery of the rotor. The rotor may
include a grooved bore. The grooved bore may be combined with the
grooved or paddled periphery. The paddles and grooves generate a
hydrostatic thrust forces during rotation of the rotor.
[0012] The pump may include both the hydrostatic and magnetic
thrust bearings. In addition, the pump may incorporate a
hydrodynamic thrust or a hydrodynamic radial bearing, or both.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention is illustrated by way of example and
not limitation in the figures of the accompanying drawings, in
which like references indicate similar elements and in which:
[0014] FIG. 1 illustrates a cross-section of a pump having a
passive magnetic axial bearing.
[0015] FIG. 2 illustrates one embodiment of the passive magnetic
axial bearing.
[0016] FIG. 3 illustrates center and off-center placement of the
passive magnetic axial bearing.
[0017] FIG. 4 illustrates one embodiment of a passive magnetic
repulsive axial bearing.
[0018] FIG. 5 illustrates one embodiment of a passive magnetic
repulsive axial bearing.
[0019] FIG. 6 illustrates an axial hydrostatic bearing in a first
position.
[0020] FIG. 7 illustrates an axial hydrostatic bearing in a second
position.
[0021] FIG. 8 illustrates one embodiment of an impeller.
[0022] FIG. 9 illustrates an alternative embodiment of an impeller
with grooved surfaces for creating a hydrostatic bearing.
[0023] FIG. 10 illustrates an alternative embodiment of an impeller
with bladed surfaces for creating a hydrostatic bearing.
[0024] FIGS. 11A and 11B illustrate embodiments of grooved surfaces
for creating hydrostatic bearings.
[0025] FIG. 12 illustrates one embodiment of the pump used in a
medical application.
DETAILED DESCRIPTION
[0026] FIG. 1 illustrates one embodiment of a centrifugal blood
pump. The pump comprises a housing 110 defining a pumping chamber
112 between an inlet 114 and an outlet 116. Within the pumping
chamber, a rotor 120 rotates about a spindle 130 protruding from a
base of the pump housing. The rotor further comprises a bladed
portion defining an impeller that provides the fluid moving
surfaces. The impeller comprises one or more blades 121 that move
fluids when the impeller rotates.
[0027] The terms "rotor" and "impeller" may be used interchangeably
in some contexts. For example, when the rotor is rotating, the
blade portion of the rotor is inherently rotating such that
reference to rotation of either the impeller or the rotor is
sufficient to describe both. When necessary, however, the term
"non-bladed portion of the rotor" or "rotor excluding the impeller"
may be used to specifically identify portions of the rotor other
than the blades. Each blade of the rotor may separately be referred
to as an impeller, however the term "impeller" is generally used to
refer to a collective set of one or more blades.
[0028] The pump is based upon a moving magnet axial flux gap motor
architecture. In one embodiment, the motor is a brushless DC motor.
Drive magnets 122 carried by the rotor have magnetic vectors
parallel to the rotor axis of rotation 190. In the illustrated
embodiment, the drive magnets are disposed within a non-bladed
portion of the rotor.
[0029] Drive windings 140 are located within the pump housing.
Power is applied to the drive windings to generate the appropriate
time-varying currents that interact with the drive magnets in order
to cause the impeller to rotate. A back iron 150 enhances the
magnetic flux produced by the motor rotor magnets. In one
embodiment, either the face 124 of the bottom of the rotor or the
opposing face 118 provided by the lower pump housing have surfaces
(e.g., 172) contoured to produce a hydrodynamic bearing when the
clearance between the rotor and the housing falls below a
pre-determined threshold. In one embodiment, the pre-determined
threshold is within a range of 0.0002 inches to 0.003 inches.
[0030] The natural attraction between the back iron 150 and the
drive magnets 122 carried by the rotor can create a significant
axial load on the rotor. This axial load is present in centrifugal
pumps based on an axial flux gap motor architecture such as Wampler
or Woodard. Woodard and Wampler both rely on hydrodynamic thrust
bearings to overcome this axial loading force. Despite the lack of
contact, hydrodynamic bearings can still damage blood cells as a
result of shear forces related to the load carried by the
hydrodynamic bearings.
[0031] The repulsive radial magnetic bearing of Wampler exacerbates
the axial loads created by the magnetic attraction between the
drive magnets and the back iron. Although the repulsive radial
magnetic bearing creates radial stability, it introduces
considerable axial instability. This axial instability can
contribute further to the axial loading. This additional axial
loading creates greater shear forces for any axial hydrodynamic
bearing that can cause undesirable hemolysis for blood
applications. In addition, the power required to sustain the
hydrodynamic bearing increases as the load increases. Thus highly
loaded hydrodynamic bearings can impose a significant power
penalty.
[0032] The blood pump of FIG. 1 includes a magnetic axial bearing
that serves to reduce or offset the axial load imposed on the rotor
by the interaction between the drive magnets and the back iron. The
axial magnetic bearing is formed by the interaction between a
spindle magnet assembly 160 disposed within the spindle and a rotor
magnet assembly 180 carried by the rotor. In the illustrated
embodiment, the rotor magnet assembly 180 is disposed proximate the
impeller, but the magnets of the rotor magnet assembly are not
located within the blades. A set screw 134 permits longitudinal
adjustment of the axial position of the axial magnetic bearing by
moving the spindle magnet assembly along a longitudinal axis of the
spindle.
[0033] FIG. 2 illustrates one embodiment of the axial magnetic
bearing. The rotor magnet assembly includes a first rotor bearing
magnet 282 and a second rotor bearing magnet 284 proximately
disposed to each other. The first and second rotor bearing magnets
are permanent magnets. In one embodiment, a pole piece 286 is
disposed between them. A pole piece or flux concentrator serves to
concentrate the magnetic flux produced by rotor bearing magnets 282
and 284. In an alternative embodiment, element 286 is merely a
spacer to aid in positioning the first and second bearing magnets
282, 284 and does not serve to concentrate any magnetic flux. In
other embodiments, element 286 is omitted so that the rotor magnet
assembly does not include a spacer or a pole piece element.
[0034] In one embodiment, elements 282 and 284 are monolithic,
ring-shaped permanent magnets (see, e.g., 250 (a)). In alternative
embodiments, the bearing magnets may be non-monolithic compositions
(see, e.g,. 250 (b), (c), (d)). For example, a bearing magnet may
be composed of a plurality of pie-shaped, or arcuate segment-shaped
(250 (b)), or other shapes (250 (c), (d)) of permanent magnet
elements that collectively form a ring-shaped permanent magnet
structure.
[0035] The rotor axial bearing magnet assembly is distinct from the
drive magnets 222 carried by a portion of the rotor other than the
blades 221. In the illustrated embodiment, the drive magnets are
disposed within the non-bladed portion 228 of the rotor.
[0036] The spindle magnet assembly includes a first spindle bearing
magnet 262 and a second spindle bearing magnet 264. The first and
second spindle bearing magnets are permanent magnets. In one
embodiment, a pole piece 266 is disposed between them. Pole piece
266 concentrates the magnetic flux produced by the spindle bearing
magnets 262 and 264. In an alternative embodiment, element 266 is
merely a spacer for positioning the first and second spindle
bearing magnets and does not serve to concentrate any magnetic
flux. In other embodiments, element 266 is omitted so that the
spindle magnet assembly does not include a spacer or a pole piece
element.
[0037] In the illustrated embodiment, permanent magnets 262 and 264
are cylindrical. Other shapes may be utilized in alternative
embodiments. The ring-shaped rotor magnets rotate with the impeller
about a longitudinal axis of the spindle that is shared by the
spindle bearing magnet assembly.
[0038] The permanent magnets of each of the spindle and rotor
bearing assemblies are arranged such that the magnetic vectors of
the individual magnets on either side of the intervening pole
pieces oppose each other. Each side of a given pole piece is
adjacent the same pole of different magnets. Thus the magnetic
vectors of magnets 262 and 264 oppose each other (e.g., N-to-N or
S-to-S). Similarly, the magnetic vectors of magnets 282 and 284
oppose each other.
[0039] The orientation of the magnets is chosen to establish an
axial attraction whenever the bearings are axially misaligned. Note
that the relative orientations of the spindle and rotor magnet
assemblies are selected so that the spindle and rotor magnet
assemblies attract each other (e.g., S-to-N, N-to-S). The magnet
vector orientation selected for the magnets of one assembly
determines the magnetic vector orientation for the magnets of the
other assembly. Table 292 illustrates the acceptable magnetic
vector combinations for the first and second rotor bearing magnets
(MR1, MR2) and the first and second spindle bearing magnets (MS1,
MS2). Forces such as the magnetic attraction between the back iron
and drive magnets that tend to axially displace the magnet bearing
assemblies are offset at least in part by the magnetic attraction
between the axial bearings that provide an axial force to restore
the axial position of the rotor.
[0040] FIG. 2 also illustrates wedges or tapered surfaces 272 that
form a portion of a hydrodynamic bearing when the clearance between
a face of the non-bladed portion of the rotor (see, e.g., bottom
face 124 of FIG. 1) and the back of the pump housing falls below a
pre-determined threshold. In various embodiments, this
pre-determined threshold is within a range of 0.0002 inches to
0.003 inches. Thus in one embodiment, the pump includes an axial
hydrodynamic bearing. The surface geometry providing the axial
hydrodynamic bearing may be located on the rotor or the
housing.
[0041] Although the spindle magnet assembly is intended to provide
an axial magnetic bearing, the attractive force between the spindle
and rotor magnet assemblies also has a radial component. This
radial component may be utilized to offset radial loading of the
impeller due to the pressure gradient across the impeller. The
radial component also serves as a pre-load during initial rotation
and a bias during normal operation to prevent eccentric rotation of
the rotor about the spindle. Such an eccentric rotation can result
in fluid whirl or whip which is detrimental to the pumping action.
The biasing radial component helps to maintain or restore the
radial position of the rotor and the pumping action, for example,
when the pump is subjected to external forces as a result of
movement or impact.
[0042] Instead of a spindle magnet assembly interacting with a
rotor bearing magnet assembly to form the magnetic bearing, a
ferromagnetic material might be used in lieu of one of a) the
spindle magnet assembly, or b) the rotor bearing magnet assembly
(but not both) in alternative embodiments.
[0043] The alternative magnetic bearing is still composed of a
spindle portion and a rotor portion, however, one of the spindle
and the rotor portions utilizes ferromagnetic material while the
other portion utilizes permanent magnets. The ferromagnetic
material interacts with the magnets to create a magnetic attraction
between the rotor and spindle. Examples of ferromagnetic materials
includes iron, nickel, and cobalt.
[0044] In one embodiment, the ferromagnetic material is "soft
iron". Soft iron is characterized in part by a very low coercivity.
Thus irrespective of its remanence or retentivity, soft iron is
readily magnetized (or re-magnetized) in the presence of an
external magnetic field such as those provided by the permanent
magnets of the magnetic bearing system.
[0045] FIG. 3 illustrates various locations for the placement of
the spindle portion of the magnetic bearing. In one embodiment, the
spindle magnet assembly 360 is axially aligned with a longitudinal
axis 390 of the spindle so that the spindle and spindle magnet
assembly share the same central longitudinal axis. In an
alternative embodiment, the spindle magnet assembly is radially
offset so that the spindle and spindle magnet assembly do not share
the same central axis. In particular, the longitudinal axis 362 of
the spindle magnet assembly 360 is displaced from the longitudinal
axis 390 of the spindle. This latter positioning may be desirable
to provide some radial biasing force. A difference in pressure
across the impeller tends to push the impeller radially towards one
side of the pump housing. This radial load may be offset at least
in part by offsetting the spindle magnet assembly.
[0046] Although the spindle and rotor magnet assemblies are
illustrated as comprising 2 magnetic elements each, the magnet
assemblies may each comprise a single magnet instead. A greater
spring rate may be achieved with multiple magnetic elements per
assembly configured as illustrated instead of a single magnet per
assembly. The use of two magnetic elements per assembly results in
a bearing that tends to correct bi-directional axial displacements
from a position of stability (i.e., displacements above and below
the point of stability) with a greater spring rate than single
magnetic elements per assembly.
[0047] FIG. 4 illustrates an alternative axial magnetic bearing.
The axial magnetic bearing is based upon axially repulsive magnetic
forces generated between the rotor 420 and the spindle 430. The
axial magnetic bearing is formed from opposing upper magnets in the
rotor and spindle and opposing lower magnets in the rotor and
spindle.
[0048] In the illustrated embodiment, the rotor includes one or
more upper bearing magnetic elements 482 and one or more lower
bearing magnetic elements 484. The spindle includes one or more
upper bearing magnetic elements 462 and one or more lower bearing
magnetic elements 464. The spindle and rotor upper bearing magnet
elements (462, 482) are positioned so that their respective
magnetic vectors oppose each other as illustrated. Similarly, the
spindle and rotor lower bearing magnet elements (464, 484) are
positioned so that their respective magnetic vectors oppose each
other as illustrated.
[0049] FIG. 5 illustrates one embodiment of the upper and lower
magnetic elements forming the upper and lower magnetic bearings in
the spindle and rotor. The rotor upper 582 and lower 584 magnetic
elements are ring-shaped. The upper and lower rings may each be
formed from a single magnet or a plurality of distinct magnetic
elements. The opposing spindle upper 562 and lower 564 magnetic
elements are similarly ring-shaped.
[0050] The magnetic vectors of the upper rotor and upper spindle
bearing magnets oppose each other. Similarly, the magnetic vectors
of the lower rotor and lower spindle bearing magnets oppose each
other. Given that there is no magnetic coupling between the upper
and lower spindle magnet elements the relative magnetic vector
orientation between the upper and lower spindle magnetic elements
is irrelevant. Similarly, the relative magnetic vector orientation
between the upper and lower rotor magnetic elements is irrelevant.
Table 592 sets forth a number of combinations for the magnetic
vectors of the upper rotor (UR), upper spindle (US), lower rotor
(LR), and lower spindle (LS) magnetic elements.
[0051] The magnetic force generated by the axial magnetic bearing
will exhibit a radial component in addition to their axial
components. The radial component will tend to de-stabilize the
rotor. In particular, the radial component may introduce radial
position instability for the magnetic bearings of either FIG. 1 or
4.
[0052] This radial instability may be overcome using radial
hydrodynamic bearings. Referring to FIG. 4, the pump may be
designed for a radial hydrodynamic bearing (i.e., hydrodynamic
journal bearing) located between the spindle 430 and the rotor
along the bore of the rotor. Alternatively, the pump may be
designed for a radial hydrodynamic bearing located between the
periphery 422 of the rotor and the wall 412 of the lower portion of
housing 410. In one embodiment, the pump includes both a radial
hydrodynamic bearing (i.e., hydrodynamic journal bearing) in both
locations.
[0053] The clearances illustrated in FIG. 4 are exaggerated.
Hydrodynamic journal bearings require narrow clearances to be
effective. In various embodiments, the hydrodynamic journal bearing
clearances range from 0.0005-0.020 inches. Although the pump of
FIG. 4 has been provided as an example, the radial hydrodynamic
bearing(s) may similarly be incorporated into the pump of FIG. 1.
The surface geometries suitable for axial (thrust) or radial
(journal) hydrodynamic bearings may be located on either the rotor
or on an associated portion of the housing (or spindle). In one
embodiment, the surface geometry includes features such as one or
more pads (i.e., a feature creating an abrupt change in clearance
such as a step of uniform height). In alternative embodiments, the
surface geometry includes features such as one or more tapers.
[0054] Another type of non-contacting bearing is a hydrostatic
bearing. FIGS. 6 and 7 illustrate a pump with an axial hydrostatic
thrust bearing. The axial hydrostatic bearing may be combined with
or used in lieu of the axial magnetic thrust bearings of FIGS.
1-5.
[0055] The axial hydrostatic forces are created by the rotor during
rotation. Referring to FIGS. 6 and 7, the spindle 630, 730 includes
a step 634, 734 that serves to regulate the hydrostatic bearing and
the axial position of the rotor.
[0056] FIG. 7 illustrates starting conditions for the pump. When
the rotor 720 rotates, a pressure differential rapidly develops
between the area above the impeller blades and the area 794 between
the blades and lower housing. When there is no gap between the step
734 and the rotor, the pressure in area 794 will be greater than
the pressure above the blades creating lift for the rotor. As the
rotor lifts away from the lower housing, the gap between the step
794 and rotor 720 increases.
[0057] Referring to FIG. 6, once the rotor lifts away from the
lower housing and the step 634, a pressure relief path becomes
available through the bore of the rotor. If the hydrostatic
pressure is too great, the rotor will move away from the lower
housing toward the pump inlet 614. This increases gap 694. In the
illustrated embodiment, the spindle includes a head portion that
serves as a rotor stop to prevent the rotor from translating too
far along the longitudinal axis of the spindle. The spindle,
however, may omit the head portion in an alternative
embodiment.
[0058] As the rotor moves towards the lower housing, gap 694
decreases. This restricts the pressure relief path through the bore
and allows pressure to start building below the blades again. The
step (634, 734) serves as a self-regulating throttle for the axial
hydrostatic bearing.
[0059] The term "step" refers to a transition in cross-sectional
area. In one embodiment the cross-section is circular. The size of
the gap 694 is a function of the displacement of the rotor from the
lower housing and the shape or profile of the step 634 and of the
opposing portion 636 of the rotor.
[0060] Mathematically, the profile of the step may consist of one
or more discontinuities aside from the endpoints defined by the
spindle and the housing. Referring to callout 650, the transition
between the spindle and the housing may be continuous (650 (b),
(c), (d)). Alternatively, the transition may comprise one (e.g.,
650 (a)) or more (e.g., 650 (e)) discontinuities. In the
illustrated variations, the profile of the step is monotonic. Any
curvature of the profile between discontinuities (or between the
endpoints) may be concave 650 (b) or convex 650 (c).
[0061] The slope of the profile of the step may vary between
discontinuities or the endpoints. Profile 650 (d) for example,
corresponds to a conical step (i.e., a step formed of a conical
frustum). Profile 650 (e) corresponds to a series of stacked
conical frustums.
[0062] In various embodiments, the profile of the opposing portion
636 of the rotor is substantially complementary to the profile of
the step 634. Generally in such cases, there is a rotor axial
displacement for which the gap is substantially constant (see,
e.g., profiles (a), (b), (c), and (e)). Alternatively, the opposing
portion 636 of the rotor need not be precisely complementary to the
step 634. Thus there may not be a rotor axial displacement for
which the gap between the step 634 and opposing portion 636 of the
rotor is constant (see, e.g., profiles 650 (d), (f)). The step and
opposing portion of the rotor illustrated in profile (d), for
example, are both generally conical but have different slopes.
Profile 650 (f) illustrates a curved step working in conjunction
with a conical opposing portion of the rotor.
[0063] FIG. 8 illustrates one embodiment of the rotor 800 including
an impeller. The rotor 800 includes a plurality of blades 820 used
for pumping the working fluid such as blood. The rotor includes a
bore 810. The rotor bore is coaxially aligned with the longitudinal
axis of the spindle within the pump housing. Drive magnets (not
illustrated) are disposed within the non-bladed portion 830 of the
rotor (i.e., within the rotor but not within any blades of the
impeller portion of the rotor). The motor rotor and pump impeller
are thus integrated so that a drive shaft is not required.
Elimination of the drive shaft also permits elimination of shaft
seals for the pump.
[0064] FIG. 9 illustrates an alternative embodiment of the rotor.
Rotor 900 similarly includes a bore 910 and a plurality of pumping
blades 920. The rotor includes additional features to create
hydrostatic thrust forces while rotating. In one embodiment, the
rotor has a grooved bore. In particular, the bore has one or more
helical grooves 950. The bore grooves have a non-zero axial pitch.
The groove is in fluid communication with the working fluid of the
pump during operation of the pump.
[0065] Alternatively or in addition to the grooved bore, the rotor
includes a plurality of grooves 940 located at a periphery of the
rotor. The peripheral grooves may be located exclusively on the
non-bladed portion of the rotor as illustrated in which case the
peripheral grooves extend from a lower face 922 to an upper face
924 of the rotor. In an alternative embodiment, the peripheral
grooves extend from the lower face 922 to the top of the blades 920
as indicated by groove 942. The peripheral grooves and bore grooves
provide hydrostatic thrust during rotation of the rotor. Various
embodiments include the bore groove, the peripheral grooves, or
both.
[0066] FIG. 10 illustrates another embodiment of the rotor. Rotor
1000 includes a bore 1010, a non-bladed portion 1030, and a
plurality of pumping blades 1020. The rotor may have grooves 1050
within the bore. The rotor includes paddles 1040 located at the
periphery of the rotor. The paddles 1040 are distinct from any
pumping blades 1020. The grooved bore and peripheral paddles
provide hydrostatic thrust during rotation of the rotor. Various
embodiments include the bore groove, the peripheral paddles, or
both.
[0067] Aside from any magnetic or hydrostatic bearings, the pump
may include a hydrodynamic bearing as described with respect to
FIGS. 1 and 4. Hydrodynamic bearings rely on the geometry and the
relative motion of two surfaces to generate pressure. The rotor or
the housing or both may include features to support a hydrodynamic
bearing. Various surface geometries suitable for hydrodynamic
bearings include grooves and tapers. The groove or taper patterns
and location of the grooves or tapers may be chosen to meet
specific design constraints. In various embodiments, one of the
hydrodynamic surfaces has grooves arranged in a spiral or a spiral
herringbone pattern.
[0068] Referring to FIG. 9, for example, the rotor may include
features at its periphery to generate a radial hydrodynamic
bearing. The radius of the periphery of the non-bladed portion of
the rotor 930, for example, may vary in size to create a taper
between the grooves. Referring to 970 (a), the radial distances
(R1, R2) measured from the center of the rotor to two different
points along the periphery of the rotor between the grooves is
substantially the same such that R1=R2. Referring to 970 (b), the
radial distances (R1, R2) measured from the center of the rotor to
two different points between the grooves of the rotor are
substantially distinct. In one embodiment, R1<R2 to create a
tapered outer periphery between the grooves.
[0069] FIGS. 11A and 11B illustrate embodiments of surface
geometries suitable for thrust or journal hydrodynamic bearings.
The surface geometries comprise groove patterns for axial (thrust)
and radial (journal) hydrodynamic bearings. The groove patterns may
be located on either the rotor or on an associated portion of the
housing (or spindle).
[0070] FIG. 11A illustrates a groove pattern for an axial
hydrodynamic bearing. Although the groove pattern is illustrated as
being disposed on the bottom of rotor 1100 (see, e.g., reference
124 of FIG. 1), the groove pattern may alternatively be located on
the lower housing portion that faces the bottom of the rotor (see,
e.g., reference 118 of FIG. 1).
[0071] Rotor 1100 includes a plurality of nested grooves. Grooves
1102 and 1104, for example, form a curved groove pair that is
"nested" within another groove pair 1106. The illustrated groove
patterns may also be described as a herringbone or spiraled
herringbone pattern. When the rotor rotates in the direction
indicated, hydrodynamic thrust forces (i.e., orthogonal to the
rotor base) are generated to push the bottom of the rotor away from
the facing lower housing portion when the clearance between the
bottom of the rotor and the lower housing portion falls below a
pre-determined threshold.
[0072] FIG. 11B illustrates one embodiment of a rotor bore
cross-section 1150 exhibiting a groove pattern suitable for a
radial hydrodynamic bearing relative to the rotor axis of rotation
1190. This groove pattern may reside on the rotor bore surface as
shown or on the periphery of the rotor. Alternatively, the groove
pattern may reside on the spindle or on the wall of the pumping
chamber (opposing the periphery of the rotor). As with the example
of FIG. 11A, the grooves are nested. This pattern is referred to as
a herringbone groove. With respect to FIGS. 11A or 11B, the grooves
may be chemically, thermally, or mechanically etched into the
surface they are disposed upon.
[0073] The grooved bore and peripheral grooves or paddles
effectively generate auxiliary hydrostatic thrust forces that are
applied to the backside of the rotor. These auxiliary hydrostatic
axial forces supplement the hydrostatic forces generated by the
impeller blades.
[0074] In various embodiments, the axial hydrostatic bearing may be
combined with a radial hydrodynamic bearing as discussed with
respect to FIGS. 1 and 4. Referring to FIG. 9, the grooved bore 910
may support both hydrodynamic journal bearing as well as an axial
(thrust) hydrostatic bearing. Preferably, however, the bore is not
relied upon for both hydrodynamic journal and thrust bearings.
Hydrostatic thrust and hydrodynamic journal bearings may, however,
be combined at the periphery of the rotor. Obviously, the rotors of
FIGS. 8-9 have greater suitability for the peripheral hydrodynamic
bearing than the paddled rotor of FIG. 10.
[0075] FIG. 12 illustrates the pump 1210 operationally coupled to
move a working fluid 1240 from a source 1220 to a destination 1230.
A first working fluid conduit 1222 couples the source to the pump
inlet 1214. A second working fluid conduit 1232 couples the pump
outlet 1216 to the destination. The working fluid is the fluid
moved by the pump from the source to the destination. In a medical
application, for example, the working fluid might be blood. In one
embodiment, the source and destination are arteries such that the
pump moves blood from one artery to another artery.
[0076] Various "contactless" bearing mechanisms have been described
as alternatives to mechanical contact bearings for rotary pumps. In
particular, rotor, impeller, and housing design features are
provided to achieve hydrodynamic, hydrostatic, or magnetic
bearings. These design features may be used in conjunction with
each other, if desired.
[0077] In the preceding detailed description, the invention is
described with reference to specific exemplary embodiments thereof.
Various modifications and changes may be made thereto without
departing from the broader spirit and scope of the invention as set
forth in the claims. The specification and drawings are,
accordingly, to be regarded in an illustrative rather than a
restrictive sense.
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