U.S. patent application number 14/202524 was filed with the patent office on 2014-09-18 for electric fluid pump.
This patent application is currently assigned to HITACHI AUTOMOTIVE SYSTEMS, LTD.. The applicant listed for this patent is HITACHI AUTOMOTIVE SYSTEMS, LTD.. Invention is credited to Shigeo KUBA.
Application Number | 20140271279 14/202524 |
Document ID | / |
Family ID | 51419277 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140271279 |
Kind Code |
A1 |
KUBA; Shigeo |
September 18, 2014 |
ELECTRIC FLUID PUMP
Abstract
An electric fluid pump includes a rotor including a permanent
magnet, and including a radially outer peripheral surface covered
by resin. An impeller faces a first axial end side of the rotor. A
support shaft is disposed in a hole, wherein the hole extends
axially of the rotor and the impeller, and through radially inside
of the rotor and the impeller. A plain bearing part is configured
to support the rotor and the impeller rotatably with respect to the
support shaft. A first groove is formed in the radially outer
peripheral surface of the rotor, and extends from the first axial
end side of the rotor to a second axial end side of the rotor
opposite to the first axial end side.
Inventors: |
KUBA; Shigeo; (Isesaki-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI AUTOMOTIVE SYSTEMS, LTD. |
Hitachinaka-shi |
|
JP |
|
|
Assignee: |
HITACHI AUTOMOTIVE SYSTEMS,
LTD.
Hitachinaka-shi
JP
|
Family ID: |
51419277 |
Appl. No.: |
14/202524 |
Filed: |
March 10, 2014 |
Current U.S.
Class: |
417/420 |
Current CPC
Class: |
F04D 13/064 20130101;
F04D 25/06 20130101; F04D 29/588 20130101; F04D 13/0606
20130101 |
Class at
Publication: |
417/420 |
International
Class: |
F04D 25/06 20060101
F04D025/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2013 |
JP |
2013-050179 |
Claims
1. An electric fluid pump comprising: a rotor including a permanent
magnet, and including a radially outer peripheral surface covered
by resin; an impeller facing a first axial end side of the rotor; a
support shaft disposed in a hole, wherein the hole extends axially
of the rotor and the impeller, and through radially inside of the
rotor and the impeller; a plain bearing part configured to support
the rotor and the impeller rotatably with respect to the support
shaft; and a first groove formed in the radially outer peripheral
surface of the rotor, and extending from the first axial end side
of the rotor to a second axial end side of the rotor opposite to
the first axial end side.
2. The electric fluid pump as claimed in claim 1, further
comprising a second groove formed in an axial end surface of the
second axial end side of the rotor, and extending from a radially
inside end side of the rotor to a radially outside end side of the
rotor.
3. The electric fluid pump as claimed in claim 2, wherein: the
permanent magnet is inside of the rotor; and the second groove
extends from a location inside of the permanent magnet outwardly in
a radial direction of the rotor.
4. The electric fluid pump as claimed in claim 2, wherein: the
rotor includes a rotor core in which the permanent magnet is
disposed; and the second groove extends from a location inside of
the rotor core outwardly in a radial direction of the rotor.
5. The electric fluid pump as claimed in claim 2, wherein the
second groove includes a longitudinal end at the radially outside
end side, wherein the longitudinal end is inside of the radially
outer peripheral surface of the rotor in a radial direction of the
rotor, and close to a longitudinal end of the first groove at the
second axial end side of the rotor in a circumferential direction
of the rotor.
6. The electric fluid pump as claimed in claim 1, wherein: the
rotor includes therein the permanent magnet as a first permanent
magnet and includes therein a second permanent magnet adjacent to
the first permanent magnet in a circumferential direction of the
rotor; and the first groove is arranged between the first permanent
magnet and the second permanent magnet in the circumferential
direction, and configured to accommodate part of a coil for
magnetizing the permanent magnets.
7. The electric fluid pump as claimed in claim 1, wherein the
electric fluid pump is a water pump configured to suck and
discharge water by rotation of the impeller.
8. An electric fluid pump comprising: a rotor including a permanent
magnet; an impeller facing a first axial end side of the rotor; a
support shaft disposed in a hole, wherein the hole extends axially
of the rotor and the impeller, and through radially inside of the
rotor and the impeller; a plain bearing part configured to support
the rotor and the impeller rotatably with respect to the support
shaft; a first groove formed in a radially outer peripheral surface
of the rotor, and extending from the first axial end side of the
rotor to a second axial end side of the rotor opposite to the first
axial end side; and a second groove formed in an axial end surface
of the second axial end side of the rotor, and extending from a
radially inside end side of the rotor to a radially outside end
side of the rotor.
9. The electric fluid pump as claimed in claim 8, wherein: the
permanent magnet is inside of the rotor; and the second groove
extends from a location inside of the permanent magnet outwardly in
a radial direction of the rotor.
10. The electric fluid pump as claimed in claim 8, wherein: the
rotor includes a rotor core in which the permanent magnet is
disposed; and the second groove extends from a location inside of
the rotor core outwardly in a radial direction of the rotor.
11. The electric fluid pump as claimed in claim 8, wherein the
second groove includes a longitudinal end at the radially outside
end side, wherein the longitudinal end is inside of the radially
outer peripheral surface of the rotor in a radial direction of the
rotor, and close to a longitudinal end of the first groove at the
second axial end side of the rotor in a circumferential direction
of the rotor.
12. The electric fluid pump as claimed in claim 8, wherein: the
rotor includes therein the permanent magnet as a first permanent
magnet and includes therein a second permanent magnet adjacent to
the first permanent magnet in a circumferential direction of the
rotor; and the first groove is arranged between the first permanent
magnet and the second permanent magnet in the circumferential
direction, and configured to accommodate part of a coil for
magnetizing the permanent magnets.
13. The electric fluid pump as claimed in claim 8, wherein the
electric fluid pump is a water pump configured to suck and
discharge water by rotation of the impeller.
14. An electric fluid pump comprising: a rotor configured to be
rotationally driven by an electromagnetic force; an impeller
disposed coaxially with the rotor; a support shaft disposed in a
hole, and configured to support the rotor and the impeller
rotatably through a plain bearing part, wherein the hole extends
axially of the rotor and the impeller, and through radially inside
of the rotor and the impeller; and an outflow forcing system
configured to force part of fluid by centrifugal force acting on
the fluid to flow out to a second axial end side of the impeller
and the rotor through a clearance between the support shaft and the
hole, wherein the fluid is sucked by rotation of the impeller from
a first axial end side of the impeller and the rotor opposite to
the second axial end side.
15. The electric fluid pump as claimed in claim 14, wherein the
electric fluid pump is a water pump configured to suck and
discharge water by rotation of the impeller.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an electric fluid pump.
[0002] Japanese Patent Application Publication No. 2006-296125
discloses an electric fluid pump that includes a rotor and an
impeller rotatably supported with respect to a support shaft
disposed in a hole, wherein the hole extends axially of the rotor
and the impeller, and through radially inside of the rotor and the
impeller.
SUMMARY OF THE INVENTION
[0003] In the electric fluid pump described above, it is possible
that depositing of foreign objects between the support shaft and
the hole may wear the support shaft and others.
[0004] In view of the foregoing, it is desirable to provide an
electric fluid pump in which a support shaft and others are
suppressed from being worn.
[0005] According to one aspect of the present invention, an
electric fluid pump comprises: a rotor including a permanent
magnet, and including a radially outer peripheral surface covered
by resin; an impeller facing a first axial end side of the rotor; a
support shaft disposed in a hole, wherein the hole extends axially
of the rotor and the impeller, and through radially inside of the
rotor and the impeller; a plain bearing part configured to support
the rotor and the impeller rotatably with respect to the support
shaft; and a first groove formed in the radially outer peripheral
surface of the rotor, and extending from the first axial end side
of the rotor to a second axial end side of the rotor opposite to
the first axial end side.
[0006] According to another aspect of the present invention, an
electric fluid pump comprises: a rotor including a permanent
magnet; an impeller facing a first axial end side of the rotor; a
support shaft disposed in a hole, wherein the hole extends axially
of the rotor and the impeller, and through radially inside of the
rotor and the impeller; a plain bearing part configured to support
the rotor and the impeller rotatably with respect to the support
shaft; a first groove formed in a radially outer peripheral surface
of the rotor, and extending from the first axial end side of the
rotor to a second axial end side of the rotor opposite to the first
axial end side; and a second groove formed in an axial end surface
of the second axial end side of the rotor, and extending from a
radially inside end side of the rotor to a radially outside end
side of the rotor.
[0007] According to a further aspect of the present invention, an
electric fluid pump comprises: a rotor configured to be
rotationally driven by an electromagnetic force; an impeller
disposed coaxially with the rotor; a support shaft disposed in a
hole, and configured to support the rotor and the impeller
rotatably through a plain bearing part, wherein the hole extends
axially of the rotor and the impeller, and through radially inside
of the rotor and the impeller; and an outflow forcing system
configured to force part of fluid by centrifugal force acting on
the fluid to flow out to a second axial end side of the impeller
and the rotor through a clearance between the support shaft and the
hole, wherein the fluid is sucked by rotation of the impeller from
a first axial end side of the impeller and the rotor opposite to
the second axial end side.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a sectional view of an electric fluid pump
according to an embodiment of the present invention, taken along a
plane containing a rotation axis or central axis of the electric
fluid pump.
[0009] FIG. 2 is a perspective view of a rotator (an impeller, a
rotor, etc.) of the electric fluid pump.
[0010] FIG. 3 is a plan view of the rotator of the electric fluid
pump, showing a second axial end side of the rotator.
[0011] FIG. 4 is a schematic partial sectional view of the electric
fluid pump, taken along a plane containing a rotation axis of the
rotator of the electric fluid pump.
[0012] FIG. 5 is a partial sectional view of the electric fluid
pump with a magnetizing yoke, taken along a plane perpendicular to
a rotation axis of the rotor, with reference to a comparative
example.
DETAILED DESCRIPTION OF THE INVENTION
Overall Configuration
[0013] According to an embodiment of the present invention, an
electric fluid pump 1 is a water pump configured to suck and
discharge cooling water as a coolant or cooling medium and as
working fluid. Electric fluid pump 1 is designed for cooling, and
arranged in a circulating system connected to a radiator. For
example, when mounted on a hybrid electric vehicle, electric fluid
pump 1 supplies cooling water to an internal combustion engine, a
drive electric motor, an inverter, and others. Electric fluid pump
1 is formed as a unit, including a pumping section 2, a motor
section 3, a support shaft 4, and a control section 5 in a housing
6. Motor section 3 is configured as a drive section to drive the
pumping section 2. Control section 5 is configured to control
operation of motor section 3. Housing 6 is formed by coupling a
pump cover 61, a pump body 62, and a board housing 63. FIG. 1 is a
sectional view of electric fluid pump 1 taken along a plane
containing a rotation axis or central axis "O" of electric fluid
pump 1. FIG. 2 is a perspective view of a rotator (an impeller 20,
a rotor 31, etc.) of electric fluid pump 1. The axis O is defined
as an ideal rotation axis of the rotator with respect to housing 6,
and also identical to a central axis of support shaft 4. The
central axis or rotation axis of the rotator is represented by "P".
For ease of explanation, an x-axis is defined as extending along
the axis O (or axis P). The direction from motor section 3 (or
rotor 31) to pumping section 2 (or impeller 20) is defined as an
x-axis positive direction. FIG. 3 is a plan view of the rotator of
the electric fluid pump, showing an x-axis negative side or second
axial end side of the rotator.
Pumping Section
[0014] Pumping section 2 includes impeller 20. Impeller 20 is
rotatably mounted in a pumping chamber R1 in housing 6, which is
defined by pump cover 61 and pump body 62. Housing 6 includes a
suction port "IN" and a discharge port "OUT", wherein suction port
IN extends along the axis O and has an opening to pumping chamber
R1, and discharge port OUT extends from the periphery of pumping
chamber R1 in a plane perpendicular to the axis O and has an
opening to the outside of pumping chamber R1. By rotation of
impeller 20, cooling water is sucked through the suction port IN
into pumping chamber R1, and then flows through a discharge passage
radially outside of impeller 20, and is then discharged under
pressure through the discharge port OUT. Electric fluid pump 1 is a
centrifugal pump configured to apply pressure to the cooling water
in a radial direction by centrifugal force acting on the cooling
water when impeller 20 is rotating. Impeller 20 includes a
plurality of blades 201, and is formed of resin, as shown in FIG.
2. Impeller 20 is arranged at a first axial end side (x-axis
positive side end) of rotor 31, and substantially coaxially with
rotor 31, and formed integrally with rotor 31, and faces the
suction port IN in the x-axis direction. Each blade 201 is arranged
to extend outward in a radial direction from axis P. For example,
each blade 201 is inclined in an opposite direction to the
rotational direction of impeller 20 as followed outwardly in the
radial direction, so that blades 201 are arranged in a centrifugal
pattern as a whole. At the x-axis positive side of impeller 20, a
shroud 21 is arranged to cover half of the radially outer periphery
of impeller 20, and thereby guide the flow of the cooling water. An
O-ring S1 is disposed as a sealing member between pump cover 61 and
pump body 62, for ensuring liquid tightness of pumping chamber
R1.
Motor Section
[0015] Motor section 3 is of a revolving-field type, wherein
permanent magnets 32 as a field magnet source are provided at rotor
31, and also of a DC brushless motor. Motor section 3 is of a
so-called inner rotor type, including a stator 30 and a rotor 31,
wherein stator 30 has a hollow-cylindrical shape, and is
accommodated in a motor chamber R2 defined by pump body 62 and
others, and rotor 31 is disposed radially inside of stator 30.
Motor section 3 is an interior permanent magnet motor (IPM motor)
in which permanent magnets 32 are embedded in rotor 31. Stator 30
includes a stator core 30a and a plurality of coils 30b, wherein
stator core 30a has an annular shape, and coils 30b are wounded
around stator core 30a. When coils 30b are energized, stator 30
causes a magnetic flux radially inside of stator core 30a.
[0016] Rotor 31 includes a magnetic pole holding part 31a and a
shaft part 31b. Magnetic pole holding part 31a includes a rotor
core 310 and permanent magnets 32, and forms a cylindrical part
facing the radially inner peripheral surface of stator 30 with a
small radial clearance. The radially outer peripheral surface of
magnetic pole holding part 31a is covered by resin, and the axial
end surface (top surface) of the x-axis positive side and the axial
end surface (bottom surface) of the x-axis negative side of
magnetic pole holding part 31a are also covered by resin. Inside of
magnetic pole holding part 31a, a plurality of magnetic poles are
held to correspond to the coils 30b of stator 30, wherein north
poles and south poles are arranged alternately in the
circumferential direction. Magnetic pole holding part 31a is
rotationally driven by magnetic interaction (i.e. a magnetic force)
with stator 30. Shaft part 31b of rotor 31 is formed of resin, and
has a central axis substantially identical to the axis P similar to
magnetic pole holding part 31a. The diameter (or radial size) of
the outer periphery of shaft part 31b is slightly smaller than that
of the inner periphery of rotor core 310 described below. The first
axial end side of shaft part 31b is fixed to the x-axis negative
side of impeller 20, and the second axial end side of shaft part
31b is fixed to the x-axis positive side of magnetic pole holding
part 31a. The shaft part 31b rotates together with magnetic pole
holding part 31a as a solid unit, and thereby transmits a torque to
drive rotationally the impeller 20.
[0017] Rotor 31, which is composed of magnetic pole holding part
31a and shaft part 31b, is formed integrally with impeller 20 by
injection of resin into a mold. Alternatively, impeller 20 may be
prepared separately from rotor 31, and then fixed to rotor 31. A
support hole 313 is defined to extend along the axis P and has a
central axis identical to the axis P, extending axially of rotor 31
and impeller 20, and through radially inside of rotor 31 and
impeller 20. The radial size (or diameter) of a major part of
support hole 313 is set to increase gradually as followed from the
x-axis positive side to the x-axis negative side. At the x-axis
positive side end of shaft part 31b (where shaft part 31b is
connected to impeller 20), the end portion of the x-axis positive
side of support hole 313 is formed with a first bearing holding
part 314 which has a cylindrical shape and has a larger diameter
than the x-axis positive side end of the major part of support hole
313. On the other hand, at the x-axis negative side end of shaft
part 31b, the end portion of the x-axis negative side of support
hole 313 is formed with a second bearing holding part 315 which has
a cylindrical shape and has a larger diameter than the x-axis
negative side end of the major part of support hole 313.
[0018] A first bush 7a as a first bearing is fixedly mounted to
first bearing holding part 314. First bush 7a includes a
hollow-cylindrical body part 70 and a flange part 71, wherein the
outer periphery of body part 70 is fitted with the inner periphery
of first bearing holding part 314, and flange part 71 is provided
at the first axial end side of body part 70 and is engaged with the
x-axis positive side of impeller 20. A second bush 7b as a second
bearing is fixedly mounted to second bearing holding part 315.
Second bush 7b includes a hollow-cylindrical body part 70 and a
flange part 71, wherein the outer periphery of body part 70 is
fitted with the inner periphery of second bearing holding part 315,
and flange part 71 is provided at the first axial end side of body
part 70 and is engaged with the x-axis negative side of magnetic
pole holding part 31a of rotor 31. First and second bushes 7a, 7b
are plain bearings (or sliding bearings) made of a kind of resin
material superior in wear resistance.
[0019] Support shaft 4 is fixedly mounted to housing 6, extending
through the support hole 313 of rotor 31 and impeller 20. Support
shaft 4 supports rotor 31 and impeller 20 rotatably through the
first and second bushes 7a, 7b. The radial size (or diameter) of
the inner peripheral surface of each bush 7a, 7b is smaller than
that of support hole 313, and is slightly larger than that of the
outer peripheral surface of support shaft 4. Namely, there is a
slight radial clearance between the inner periphery of each bush
7a, 7b and the outer periphery of support shaft 4, so that first
and second bushes 7a, 7b can slide with respect to support shaft 4.
First and second bushes 7a, 7b support the rotor 31 and impeller 20
rotatably with respect to support shaft 4. The first axial end (or
x-axis positive side end) of support shaft 4 is formed with a
larger-diameter part 40. The radial size (or diameter) of the major
part of support shaft 4 except the larger-diameter part 40 is
substantially constant in the x-axis direction. The size of the
radial clearance between the inner periphery of the major part of
support hole 313 and the outer periphery of the major part of
support shaft 4 is set to increase gradually as followed from the
x-axis positive side to the x-axis negative side.
[0020] Pump cover 61 is formed with a travel restriction part 610.
Travel restriction part 610 is supported by a rib 611 and is placed
at the axis O, wherein rib 611 projects from the inner periphery of
the x-axis negative side of suction port IN of pump cover 61. The
x-axis positive side end of support shaft 4 is fixed to travel
restriction part 610 by fitting in through hole 612 of travel
restriction part 610. The x-axis positive side of support shaft 4
is thus supported by housing 6. The axial end surface of the x-axis
negative side of travel restriction part 610 and the flange part 71
of first bush 7a face each other through a small clearance in the
x-axis direction, wherein a washer 8 is disposed in this clearance
to surround the support shaft 4. Movement of impeller 20 and rotor
31 in the x-axis positive direction is restricted by sliding
contact between the flange part 71 of first bush 7a and the washer
8. A holder part 64 is fixedly mounted to the axial end of the
x-axis negative side of pump body 62. The larger-diameter part 40
of support shaft 4 is fixedly mounted to holder part 64 by fitting
in a through hole 640 of holder part 64. The x-axis negative side
of support shaft 4 is thus held by housing 6. Movement of rotor 31
and impeller 20 in the x-axis negative direction is restricted by
sliding contact between the flange part 71 of second bush 7b and
larger-diameter part 40.
Stator Accommodation Chamber and Rotor Accommodation Chamber
[0021] The x-axis positive side of pump body 62 is formed with a
separation wall part 620 which projects from the outer periphery of
pump body 62 inward in the radial direction. The radially inner
side of separation wall part 620 is formed with a
hollow-cylindrical projection part 621 which projects toward the
x-axis negative side. The x-axis positive side of the radially
inner side of separation wall part 620 is formed with a recess 622
which accommodates an x-axis negative side part of the outer
periphery of impeller 20. The motor chamber R2 in pump body 62 is
separated by separation wall member 65 to define a stator
accommodation chamber R21 and a rotor accommodation chamber R22.
Separation wall member 65 has a thin hollow-cylindrical shape and
is made of nonmagnetic metal. Separation wall member 65 includes an
outer wall part 650, a flange part 651, a larger-diameter part 652,
a flange part 653, and a smaller-diameter part 654, wherein outer
wall part 650 has a hollow-cylindrical shape, and flange part 651
extends radially outward from the opening of the x-axis positive
side of outer wall part 650, and larger-diameter part 652 has a
hollow-cylindrical shape extending toward the x-axis positive side
from the outer peripheral edge of flange part 651, and
smaller-diameter part 654 has a hollow-cylindrical shape extending
toward the x-axis negative side from the inner peripheral edge of
flange part 653. The radial size (or diameter) of to the inner
periphery of outer wall part 650 is set substantially equal to that
of the inner periphery of separation wall part 620 (projection part
621) of pump body 62, so that the inner peripheral surfaces of
outer wall part 650 and separation wall part 620 (projection part
621) are continuous and flush with each other.
[0022] The x-axis positive side end (flange part 651) of separation
wall member 65 is disposed at the x-axis negative side end of
projection part 621 of separation wall part 620 of pump body 62.
The x-axis positive side end of a hollow-cylindrical part 641 of
holder part 64 is disposed at the x-axis negative side end of
separation wall member 65, wherein the hollow-cylindrical part 641
projects toward the x-axis positive side radially outside of
through hole 640. Accordingly, stator accommodation chamber R21 is
defined radially outside of separation wall member 65 by the inner
peripheral surface of pump body 62 (including the x-axis negative
side surface of separation wall part 620), and the radially outer
peripheral surface of separation wall member 65, and the surface of
the x-axis positive side of part of holder part 64 radially outside
of the cylindrical part 641 (including the radially outer
peripheral surface of cylindrical part 641). Stator accommodation
chamber R21 has a closed annular space in which stator 30 is
mounted.
[0023] On the other hand, rotor accommodation chamber R22 is
defined radially inside of separation wall member 65 by the
radially inner peripheral surface of separation wall part 620
(projection part 621) of pump body 62, and the radially inner
peripheral surface of separation wall member 65, and the surface of
the x-axis to positive side of part of holder part 64 radially
inside of cylindrical part 641. Rotor 31 is rotatably mounted in
rotor accommodation chamber R22. Rotor accommodation chamber R22 is
an open space constantly communicating with the pumping chamber R1
at the x-axis positive side through a clearance between the x-axis
negative side of the outer periphery of impeller 20 and the
separation wall part 620 (recess 622) of pump body 62, and is
filled with the cooling water supplied from the pumping chamber R1.
Rotor accommodation chamber R22 communicates with pumping chamber
R1 through a clearance between support hole 313 (and the inner
peripheral surfaces of first and second bushes 7a, 7b) and support
shaft 4.
[0024] An O-ring S2 as a sealing member is disposed between the
radially outside of projection part 621 of separation wall part 620
and the radially inside of larger-diameter part 652 of separation
wall member 65 in pump body 62. Moreover, an O-ring S3 as a sealing
member is disposed between the radially inside of cylindrical part
641 of holder part 64 and the radially outside of smaller-diameter
part 654 of separation wall member 65. Accordingly, fluid
communication between the radially inside and the radially outside
of separation wall member 65 is shut off. In this way, stator
accommodation chamber R21 and rotor accommodation chamber R22 are
liquid-tightly separated by O-rings S2 and S3, preventing the
cooling water from flowing from rotor accommodation chamber R22
into stator accommodation chamber R21 (and a board accommodation
chamber R3 detailed below).
Control Section
[0025] Board housing 63 is attached to pump body 62, covering an
x-axis negative side opening of pump body 62, and defining therein
the board accommodation chamber R3. Board accommodation chamber R3
is defined between board housing 63 and holder part 64. Control
section 5 includes a board 50, capacitors, etc., wherein board 50
is a driver for supplying a drive current to motor section 3, and
is accommodated in board accommodation chamber R3. An electric
circuit (a CPU, transistors, etc.) is mounted on board 50, wherein
these circuit components and capacitors constitute a converter
system and a control circuit system. The converter system is
configured to receive electric supply from a battery as a direct
current power supply, and supply an alternating current to the
coils 30b of motor section 3. The control circuit system is
configured to control the converter system. The x-axis negative
side end surface of board housing 63 substantially parallel to
board 50 is formed with a heat sink.
Configuration of Rotor
[0026] Magnetic pole holding part 31a includes rotor core 310 that
is formed in a hollow-cylindrical shape by layering a plurality of
annular electromagnetic steel sheets in the direction of axis P as
shown in FIGS. 1 and 5. Rotor core 310 includes a plurality of
insertion holes 311 (six insertion hole 311 in this example), in
each of which permanent magnet 32 is inserted and mounted. Each
insertion hole 311 extends in the x-axis direction, wherein the
x-axis positive side end of insertion hole 311 is closed by the
x-axis positive side end portion of rotor core 310, and the x-axis
negative side end of insertion hole 311 is open at the x-axis
negative side end surface of rotor core 310. The openings of
insertion holes 311 are arranged around the axis P, forming six
edges of a hexagonal shape as viewed in the x-axis direction. Each
permanent magnet 32 has a plate shape. The number of permanent
magnets 32 is six in this example. Each permanent magnet 32 is
inserted and mounted in insertion hole 311 of rotor core 310 before
permanent magnet 32 is magnetized, and thereby embedded in magnetic
pole holding part 31a, and then magnetized by magnetizing yoke 9.
This forms a plurality magnetic poles arranged in the
circumferential direction.
[0027] As shown in the left side of FIG. 5, the outer periphery of
rotor core 310 is formed with recesses 312 which are close to the
ends of two adjacent insertion holes 311 in the circumferential
direction around axis P, and extend in the axial direction of rotor
31. Each recess 312 includes a first recessed portion 312a and a
second recessed portion 312b, wherein first recessed portion 312a
is relatively shallow and is close to the intermediate point
between two adjacent insertion holes 311, and second recessed
portion 312b is relatively deeper, and is located substantially at
the center of first recessed portion 312a in the circumferential
direction, and extends inward in the radial direction between two
adjacent insertion holes 311. The provision of recess 312 serves to
minimize the distance from the circumferential end of insertion
hole 311 to the outer peripheral surface of rotor core 310 (recess
312). The number of recesses 312 is equal to that of insertion
holes 311, which is six in this example.
[0028] Before rotor 31 and impeller 20 are formed integrally, a
holder 33 is assembled to rotor core 310 in which permanent magnets
32 are mounted, as shown in FIG. 1. Holder 33 is a part made of
resin for holding the permanent magnets 32. When a
hollow-cylindrical part 33a of holder 33 is fixed by fitting to the
inner periphery of rotor core 310 from the x-axis negative side, a
flange part 33b of holder 33 covers the opening of the x-axis
negative side of each insertion hole 311, and thereby prevents
permanent magnet 32 from being dropped from insertion hole 311. The
x-axis negative side surface of holder 33 is formed with a
plurality of recesses 330 (six recesses 330 in this example) which
extend radially and are arranged around axis P at substantially
equal intervals. Each recess 330 is fitted with a first projection
portion of the mold (or zig), thereby positioning the rotor core
310 (the assembly of permanent magnets 32 and holder 33) in the
mold. This positioning allows a second projection portion of the
mold to slightly enter the recess 312 formed at the outer periphery
of rotor core 310, and thereby sets rotor core 310 (the assembly of
permanent magnets 32 and holder 33) in the mold, wherein the second
projection portion is formed in the mold and extends in the x-axis
direction. Rotor 31 and impeller 20 are formed of resin integrally
with each other by injection of resin into the mold under the
condition described above. The flange part 33b of holder 33 may be
formed to cover partially the opening of the x-axis negative side
of each insertion hole 311 (namely, making the insertion hole 311
partially opened). In this case alternative case, the resin
material is supplied into each insertion hole 311 through the
partial opening, so that it is unnecessary to fix permanent magnets
32 in insertion holes 311, which results in a reduction of the
manufacturing cost.
[0029] The thus formed radially outer peripheral surface of rotor
31 is formed with a plurality of recesses referred to as first
grooves 316 (six first grooves 316 in this example), each of which
extends in the axial direction similar to recess 312 of rotor core
310, and is formed by drawing the second projection portion of the
mold, as shown in FIGS. 2 and 3. The x-axis negative side surface
of rotor 31 is formed with a plurality of recesses referred to as
second grooves 317 (six second grooves 317 in this example), each
of which extends radially similar to recess 330 of holder 33, and
is formed by drawing the first projection portion of the mold. As
shown in FIG. 2, each first groove 316 is formed in the radially
outer peripheral surface of rotor 31 (magnetic pole holding part
31a), and extends from the first axial end side (x-axis positive
side) to the second axial end side (x-axis negative side),
specifically, extends over the entire axial length of rotor 31
(magnetic pole holding part 31a). In other words, the x-axis ends
of first groove 316 are not closed as viewed in the x-axis
direction, but are open at the axial ends of rotor 31 (magnetic
pole holding part 31a). As shown in FIG. 5, each first groove 316
is located between two permanent magnets 32 (insertion holes 311)
adjacent to each other in the circumferential direction. The width
(in the circumferential direction) and the depth (in the radial
direction) of first groove 316 are set so that part of magnetizing
yoke 9 that is a coil for magnetizing the permanent magnets 32 can
be put in first groove 316.
[0030] As shown in FIG. 3, each second groove 317 is formed in the
bottom surface of the second axial end side (x-axis negative side)
of rotor 31 (magnetic pole holding part 31a), and extends from the
radially inside of rotor 31 to the radially outside of rotor 31.
The radially outside end of second groove 317 (or the longitudinal
end of second groove 317 at the radially outside of rotor 31) is
located radially inside of the radially outer peripheral surface of
rotor 31, and shifted from and has no overlap with the first
grooves 316 in the circumferential direction of rotor 31
(specifically, located at a substantially intermediate position
between two adjacent first grooves 316). As shown in FIG. 1, each
second groove 317 extends from a location radially inside of
permanent magnet 32 toward the radially outside. Specifically, each
second groove 317 extends from a location slightly radially inside
of rotor core 310 toward the radially outside.
Functions of Pump
[0031] The following describes functions of electric fluid pump 1.
The rotor 31 of motor section 3 is rotatably mounted to support
shaft 4, and is applied with a torque resulting from the magnetic
flux generated by stator 30 in response to a control signal
outputted by control section 5. Rotation of rotor 31 causes the
impeller 20 to rotate and thereby causes pumping section 2 to
operate. Rotation of impeller 20 causes fluid to be sucked from the
x-axis positive side into pumping chamber R1, and causes major part
of the fluid to be discharged through the discharge port OUT. In
the present embodiment, it is configured so that part of the sucked
fluid can smoothly flow between support shaft 4 and support hole
313. FIG. 4 is a schematic partial sectional view of electric fluid
pump 1, showing flow of the part of the fluid by an arrow of a
long-dashed short-dashed line. Rotor accommodation chamber R22
communicates with pumping chamber R1 through a clearance CL4
between the x-axis negative side of the outer periphery of impeller
20 and the separation wall part 620 (recess 622) of pump body 62,
and is filled with the cooling water. The clearance CL1 between the
support hole 313 (and the inner peripheral surfaces of first and
second bushes 7a, 7b) and the support shaft 4 communicates with
pumping chamber R1 at the x-axis positive side and rotor
accommodation chamber R22 at the x-axis negative side, and is
filled with the cooling water. The clearance CL2 between the x-axis
negative side surface of magnetic pole holding part 31a and the
x-axis positive side surfaces of holder part 64 and flange part 653
of separation wall member 65, and the clearance CL3 between the
radially outer peripheral surface of magnetic pole holding part 31a
and the radially inner peripheral surface of outer wall part 650 of
separation wall member 65, constitute part of rotor accommodation
chamber R22, and are filled with the cooling water.
[0032] Rotation of rotor 31 (magnetic pole holding part 31a) causes
centrifugal force to act on the cooling water in clearance CL2, and
thereby causes the cooling water in clearance CL2 to be pressed
toward the radially outside, and be sent to a space at the x-axis
positive side of magnetic pole holding part 31a through the
clearance CL3. When the cooling water in clearance CL2 is pressed
toward the radially outside (into clearance CL3), the cooling water
is sucked from the clearance CL1 into clearance CL2 (the function
of the centrifugal pump). Accordingly, as shown in FIG. 4, when
impeller 20 (and rotor 31) is rotating, part of the fluid sucked
into pumping chamber R1 from the x-axis positive side is sucked
from the clearance CL1 into clearance CL2, and also sent from
clearance CL2 into the space of the x-axis positive side of
magnetic pole holding part 31a through clearance CL3, and then
discharged through clearance CL4 and discharge port OUT.
[0033] First and second bushes 7a, 7b function as plain bearings in
the cooling water, so that the use environment of first and second
bushes 7a, 7b is hard about wearing. Specifically, if a foreign
object is trapped and deposited between bush 7a, 7b and support
shaft 4, it may promote wear of first and second bushes 7a, 7b
and/or support shaft 4. In the present embodiment, this problem is
overcome by the feature that electric fluid pump 1 includes a flow
forcing system for forcing the flow of part of the working fluid.
This serves to prevent depositing of foreign objects in clearance
CL1 (particularly, in the clearance between bush 7a, 7b and support
shaft 4), and thereby suppress wear of first and second bushes 7a,
7b and support shaft 4.
[0034] Specifically, the radially outer peripheral surface of rotor
31 (magnetic pole holding part 31a) is formed with first grooves
316 extending in the x-axis direction. First groove 316 serves to
increase the flow sectional area of water flow in clearance CL3,
and thereby force the cooling water to flow from clearance CL2 to
clearance CL3 by centrifugal force, and force the cooling water to
flow from the clearance CL1 to the clearance CL2. In this way,
first grooves 316 constitute an outflow forcing system configured
to force part of fluid by centrifugal force acting on the fluid to
flow out to the clearance CL2 through the clearance CL1
(particularly, between the support shaft 4 and first and second
bushes 7a, 7b). In this embodiment, first groove 316 is formed over
the entire length of rotor 31 (magnetic pole holding part 31a) in
the axial direction, so that both of the x-axis ends of first
groove 316 are opened. This serves to smooth the inflow of the
cooling water from clearance CL2 to clearance CL3 and the outflow
from clearance CL3 to the x-axis positive side of magnetic pole
holding part 31a, and thereby force the flow of the cooling water
in clearance CL1. It may be configured so that first groove 316
does not extend over the entire length of magnetic pole holding
part 31a and one or both of x-axis ends of first groove 316 is
closed. In the present embodiment, the radially outer peripheral
surface of rotor 31 (magnetic pole holding part 31a) is covered by
resin, in which first grooves 316 are formed. This serves to
produce the advantageous effects described above, while suppressing
corrosion of rotor core 310 and others.
[0035] The bottom surface of the x-axis negative side of rotor 31
(magnetic pole holding part 31a) is formed with second grooves 317
extending radially. Second groove 317 serves to increase the flow
sectional area of water flow in clearance CL2, and thereby force
the cooling water to flow from clearance CL1 to clearance CL2 by
centrifugal force. In this way, second grooves 317 constitute the
outflow forcing system as well as first grooves 316. In this
embodiment, second groove 317 extends from the location radially
inside of permanent magnet 32 toward the radially outside. This
serves to shorten the distance from clearance CL1 to the radially
inside end of second groove 317, and thereby smooth the outflow of
the cooling water from clearance CL1 to clearance CL2.
Specifically, second groove 317 extends from the location radially
inside of rotor core 310 (in which permanent magnets 32 are
embedded) toward the radially outside. This serves to shorten the
distance from clearance CL1 to the radially inside end of second
groove 317, and thereby enhance the function of electric fluid pump
1 described above.
[0036] It is optional that second groove 317 is not along a radial
straight line passing through the axis P, but may be along a
straight line extending from the radially inside to the radially
outside without passing through the axis P. As viewed in the x-axis
direction, the shape of second groove 317 is not limited to a
straight shape but may be a curbed shape. One or both of the radial
ends of second groove 317 may be opened. For example, second groove
317 may extend over the entire radial length of the bottom surface
of the x-axis negative side of rotor 31 (magnetic pole holding part
31a), so that both longitudinal ends of second groove 317 are
opened.
[0037] In the present embodiment, the radially outside end of
second groove 317 is located radially inside of the radially outer
peripheral surface of rotor 31 (magnetic pole holding part 31a) and
shifted from first grooves 316 in the circumferential direction.
Actual water flow in clearance CL2 has a component in the
circumferential direction as well as a component in the radial
direction passing through the axis P. Accordingly, even in the
configuration where the longitudinal end of second groove 317 at
the radially outside of rotor 31 is closed to the clearance CL3,
the flow path from the longitudinal end of second groove 317 to the
x-axis negative, side of first groove 316 is shortened, as compared
to cases where the shifting from first groove 316 is not adopted.
This serves to smooth the outflow of the cooling water from
clearance CL2 to clearance CL3, and thereby force the flow of the
cooling water in clearance CL1.
[0038] An additional groove may be provided to extend from the
longitudinal end of second groove 317 at the radially outside of
rotor 31 to the x-axis negative side end of first groove 316.
[0039] In the present embodiment, not only the radially outer
peripheral surface of rotor 31 (magnetic pole holding part 31a) but
also the axial end surfaces of rotor 31 are covered by resin,
wherein the axial end surface (bottom surface) of the x-axis
negative side is formed with second grooves 317. This serves to
obtain the advantageous effects described above, while reliably
suppressing corrosion of rotor core 310 and permanent magnets 32.
The feature that the recess formed by drawing the first projecting
portion of the mold (or zig) is used as second groove 317,
simultaneously provides the positioning means used for forming the
rotor 31 and impeller 20, and the flow forcing means, and thereby
reduces the manufacturing cost. Moreover, the feature that the
recess 330 formed in holder 33 is used to form second groove 317,
serves to simultaneously obtain the prevention of drop of permanent
magnets 32 by holder 33 and the ease of forming by the positioning
by recess 330, in addition to the advantageous effect described
above.
[0040] The flow sectional area of clearance CL1 between the inner
peripheral surface of the major part of support hole 313 and the
major part of support shaft 4 is set to increase gradually as
followed from the x-axis positive side to the x-axis negative side.
This serves to force the flow of the cooling water in clearance CL1
from the x-axis positive side to the x-axis negative side.
[0041] In the case where the outer peripheral surface of rotor 31
(magnetic pole holding part 31a) is covered by resin as in the
present embodiment, it may adversely affect the efficiency of
magnetizing the permanent magnets 32. FIG. 5 is a partial sectional
view of electric fluid pump 1 with magnetizing yoke 9, taken along
a plane perpendicular to the axial direction of rotor 31 (magnetic
pole holding part 31a), with reference to a comparative example.
The left side of FIG. 5 shows the present embodiment in which rotor
core 310 is formed with recesses 312 and the radially outer
peripheral surface of magnetic pole holding part 31a is formed with
first grooves 316. The right side of FIG. 5 shows the comparative
example in which no recess 312 and no first groove 316 is provided.
The magnetic field caused by one of magnetizing yokes 9 is shown by
a plurality of lines of magnetic force encompassing the magnetizing
yoke 9. In the case where the radially outer peripheral surface of
magnetic pole holding part 31a is covered by resin, the distance
from magnetizing yoke 9 to permanent magnet 32 is increased by the
thickness of film of resin, as compared to the cases no resin film
is provided. Accordingly, in the case where no first groove 316 is
provided, it is possible in general that the number of the lines of
magnetic force of magnetizing yoke 9 that fail to reach the
permanent magnet 32 is increased to reduce the magnetizing
efficiency.
[0042] In contrast, in the present embodiment, first groove 316 is
provided between two adjacent permanent magnets 32 in the
circumferential direction, to allow part of magnetizing yoke 9 to
be placed in first groove 316. Since magnetizing is performed under
the condition where part of magnetizing yoke 9 is located in first
groove 316, the distance between magnetizing yoke 9 and permanent
magnet 32 is shortened by the amount of entrance of magnetizing
yoke 9 into first groove 316, and thereby increase the number of
magnetic lines of magnetizing yoke 9 that reach the permanent
magnet 32. This enhances the magnetizing efficiency. In other
words, by commonality of the means for enhancing the magnetizing
efficiency and the means for forcing the outflow of cooling water,
it is possible to simplify the structure and thereby reduce the
manufacturing cost. In view of the magnetizing operation by
magnetizing yoke 9, it is preferable that first groove 316 has a
straight shape extending in the x-axis direction.
[0043] If first groove 316 is formed without forming the recess 312
in rotor core 310, the thickness of the resin covering the radially
outer peripheral surface of magnetic pole holding part 31a becomes
uneven between the portion where first groove 316 is formed and the
remaining portion, which is disadvantageous in the efficiency of
resin forming. This may also result in an increase in the radial
size of magnetic pole holding part 31a. In contrast, in the present
embodiment, the feature that rotor core 310 is formed with recess
312, and first groove 316 is formed in the position corresponding
to recess 312, serves to enhance the magnetizing efficiency even in
the configuration where the outer peripheral surface of magnetic
pole holding part 31a is covered by resin, and also enhance the
facility of forming by making the thickness of resin uniform. Even
if the radially outer peripheral surface of magnetic pole holding
part 31a is not covered by resin, it is naturally possible to
enhance the magnetizing efficiency by magnetizing under the
condition where part of magnetizing yoke 9 is placed in recess 312
of rotor core 310. The second groove 317, which is formed in the
bottom surface of the x-axis negative side of rotor 31 (magnetic
pole holding part 31a), is used as a means for positioning (as a
recess to be engaged with a zig) when the magnetizing is performed.
In this way, by commonality of the positioning means during
magnetizing and the outflow forcing means, it is possible to reduce
the manufacturing cost.
Advantageous Effects
[0044] The following summarizes the features of the present
embodiment and produced advantageous effects.
[0045] <1> An electric fluid pump (1) includes: a rotor (31,
magnetic pole holding part 31a) including a permanent magnet (32),
and including a radially outer peripheral surface covered by resin;
an impeller (20) facing a first axial end side of the rotor (31); a
support shaft (4) disposed in a hole (support hole 313), wherein
the hole (313) extends axially of the rotor (31) and the impeller
(20), and through radially inside of the rotor (31) and the
impeller (20); a plain bearing part (first and second bushes 7a,
7b) configured to support the rotor (31) and the impeller (20)
rotatably with respect to the support shaft (4); and a first groove
(316) formed in the radially outer peripheral surface of the rotor
(31), and extending from the first axial end side of the rotor (31)
to a second axial end side of the rotor (31) opposite to the first
axial end side. This serves to force the flow of the fluid in a
clearance (CL1) between the support shaft (4) and the hole (313) by
the first groove (316), and thereby prevent depositing of foreign
objects between the support shaft (4) and the plain bearing part
(7a, 7b), and suppress the support shaft (4) and others from being
worn. The covering the radially outer peripheral surface of the
rotor (31) by resin, serves to suppress corrosion of a rotor core
(310) and others of the rotor (31).
[0046] <2> The electric fluid pump (1) further includes a
second groove (317) formed in an axial end surface of the second
axial end side of the rotor (31), and extending from a radially
inside end side of the rotor (31) to a radially outside end side of
the rotor (31). This serves to force the flow of the fluid in a
clearance (CL1) between the support shaft (4) and the hole (313) by
the second groove (317), and thereby prevent depositing of foreign
objects between the support shaft (4) and the plain bearing part 1c
(7a, 7b), and suppress the support shaft (4) and others from being
worn.
[0047] <3> In the electric fluid pump (1): the permanent
magnet (32) is inside of the rotor (31); and the second groove
(317) extends from a location inside of the permanent magnet (32)
outwardly in a radial direction of the rotor (31). This serves to
shorten the distance from the clearance (CL1) between the support
shaft (4) and the hole (313) to the longitudinal end of the second
groove (317) at the radially inside of the rotor (31), and thereby
force the flow of the fluid in the clearance (CL1).
[0048] <4> In the electric fluid pump (1): the rotor (31)
includes a rotor core (310) in which the permanent magnet (32) is
disposed; and the second groove (317) extends from a location
inside of the rotor core (310) outwardly in a radial direction of
the rotor (31). This serves to shorten the distance from the
clearance (CL1) between the support shaft (4) and the hole (313) to
the longitudinal end of the second groove (317) at the radially
inside of the rotor (31), and thereby force the flow of the fluid
in the clearance (CL1).
[0049] <5> In the electric fluid pump (1), the second groove
(317) includes a longitudinal end at the radially outside end side,
wherein the longitudinal end is inside of the radially outer
peripheral surface of the rotor (31) in a radial direction of the
rotor (31), and close to a longitudinal end of the first groove
(316) at the second axial end side of the rotor (31) in a
circumferential direction of the rotor (31). This serves to shorten
the distance from the end of the second groove (317) at the
radially outside of the rotor (31) to the x-axis negative side end
of the first groove (316), and thereby force the flow of the fluid
in the clearance (CL1), even in the configuration where the end of
the second groove (317) at the radially outside is not opened to
the radially outer peripheral surface of the rotor (31).
[0050] <6> In the electric fluid pump (1): the rotor (31)
includes therein the permanent magnet (32) as a first permanent
magnet (32) and includes therein a second permanent magnet (32)
adjacent to the first permanent magnet (32) in a circumferential
direction of the rotor (31); and the first groove (316) is arranged
between the first permanent magnet (32) and the second permanent
magnet (32) in the circumferential direction, and configured to
accommodate part of a coil for magnetizing the permanent magnets
(32). This enhances the efficiency of magnetizing the permanent
magnet (32).
[0051] <7> An electric fluid pump (1) includes: a rotor (31)
configured to be rotationally driven by an electromagnetic force;
an impeller (20) disposed coaxially with the rotor (31); a support
shaft (4) disposed in a hole (support hole 313), and configured to
support the rotor (31) and the impeller (20) rotatably through a
plain bearing part (first and second bushes 7a, 7b), wherein the
hole (313) extends axially of the rotor (31) and the impeller (20),
and through radially inside of the rotor (31) and the impeller
(20); and an outflow forcing system (first groove 316, second
groove 317) configured to force part of fluid by centrifugal force
acting on the fluid to flow out to a second axial end side of the
impeller (20) and the rotor (31) through a clearance (CL1) between
the support shaft (4) and the hole (313), wherein the fluid is
sucked by rotation of the impeller (20) from a first axial end side
of the impeller (20) and the rotor (31) opposite to the second
axial end side. This serves to force the flow of the fluid in a
clearance (CL1) between the support shaft (4) and the hole (313) by
the outflow forcing system (316, 317), and thereby prevent
depositing of foreign objects between the support shaft (4) and the
plain bearing part (first and second bushes 7a, 7b), and thereby
suppress the support shaft 4 and others from being worn.
[0052] <8> In the electric fluid pump (1), the electric fluid
pump (1) is a water pump configured to suck and discharge water
(cooling water) by rotation of the impeller (20). This water pump
can produce the advantageous effects described above. The covering
the radially outer peripheral surface of the rotor (31, magnetic
pole holding part 31a) by resin, serves to suppress corrosion of a
rotor core (310) and others of the rotor (31) by contact with
water.
MODIFICATIONS
[0053] The embodiment described above may be modified. Although the
working fluid of the pump is water as cooling water as a coolant
medium and the configuration described above is applied to the
water pump in this embodiment, the configuration of the first
groove and others may be applied to another electric fluid pump as
long as the electric fluid pump includes a support shaft supporting
a rotor and an impeller rotatably through plain bearings, wherein
the support shaft is disposed in a hole, wherein the hole extends
axially of the rotor and the impeller, and through radially inside
of the rotor and the impeller. The coolant medium is not limited to
water.
[0054] The plain bearings may be formed integrally with the rotor
or the support shaft. In other words, the outer periphery of the
support shaft or the inner periphery of the hole where the support
shaft is disposed may be used also as a plain bearing. In this
modification, it is possible to reduce the number of parts and the
number of assembling operations. In the present embodiment, first
and second bushes 7a, 7b are provided as plain bearings separated
from rotor 31. This allows to select a material for first and
second bushes 7a, 7b independently of the material of rotor 31,
wherein the material of first and second bushes 7a, 7b may be one
superior in bearing performance and wear resistance, and thereby
enhance the function of first and second bushes 7a, 7b. First and
second bushes 7a, 7b are not limited to the positions in the x-axis
direction, the sizes, and the number in the shown example. Although
first and second bushes 7a, 7b are fixed to rotor 31, and first and
second bushes 7a, 7b slide with respect to the components (support
shaft 4 and others) stationary to housing 6 in the present
embodiment, it may be modified so that first and second bushes 7a,
7b is fixed to the components (support shaft 4 and others)
stationary to housing 6, and rotor 31 slides with respect to first
and second bushes 7a, 7b.
[0055] The entire contents of Japanese Patent Application
2013-050179 filed Mar. 13, 2013 are incorporated herein by
reference.
[0056] Although the invention has been described above by reference
to certain embodiments of the invention, the invention is not
limited to the embodiments described above. Modifications and
variations of the embodiments described above will occur to those
skilled in the art in light of the above teachings. The scope of
the invention is defined with reference to the following
claims.
* * * * *