U.S. patent application number 13/598044 was filed with the patent office on 2013-02-28 for electric pump unit.
This patent application is currently assigned to JTEKT CORPORATION. The applicant listed for this patent is Nobutsuna MOTOHASHI, Takafumi UEMOTO. Invention is credited to Nobutsuna MOTOHASHI, Takafumi UEMOTO.
Application Number | 20130052058 13/598044 |
Document ID | / |
Family ID | 46801339 |
Filed Date | 2013-02-28 |
United States Patent
Application |
20130052058 |
Kind Code |
A1 |
MOTOHASHI; Nobutsuna ; et
al. |
February 28, 2013 |
ELECTRIC PUMP UNIT
Abstract
A pump body is formed of a pump housing and a pump plate
provided in front of the pump housing. A motor housing is fixed to
a rear end of the pump housing, and accommodates a pump driving
electric motor. A bearing device that supports a motor shaft
includes a first bearing that is arranged in a closed-end hole
formed in a rear face of the pump plate and supporting a front end
portion of the motor shaft, and a second bearing that is arranged
radially inward of a cylindrical bearing support portion formed in
the pump housing and extending inside the motor housing and that
supports a middle portion of the motor shaft. A pump rotor is
arranged between the first bearing and the second bearing.
Inventors: |
MOTOHASHI; Nobutsuna;
(Katsuragi-shi, JP) ; UEMOTO; Takafumi;
(Kashiwara-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MOTOHASHI; Nobutsuna
UEMOTO; Takafumi |
Katsuragi-shi
Kashiwara-shi |
|
JP
JP |
|
|
Assignee: |
JTEKT CORPORATION
Osaka
JP
|
Family ID: |
46801339 |
Appl. No.: |
13/598044 |
Filed: |
August 29, 2012 |
Current U.S.
Class: |
417/410.4 |
Current CPC
Class: |
F01C 21/02 20130101;
F04C 11/008 20130101; F04C 2/102 20130101; F04C 2240/808 20130101;
F04C 2240/52 20130101 |
Class at
Publication: |
417/410.4 |
International
Class: |
F04C 2/08 20060101
F04C002/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2011 |
JP |
2011-188291 |
Feb 1, 2012 |
JP |
2012-019831 |
Claims
1. An electric pump unit, comprising: a pump body of a pump that
sucks in and discharges fluid, wherein the pump body includes a
pump housing and a pump plate, the pump housing forms a pump
chamber that accommodates a pump rotor, and the pump plate is
provided at one end of the pump housing; a motor housing that is
fixed to the other end of the pump housing and that accommodates a
pump driving electric motor; and the electric motor that includes a
motor shaft that is supported by a bearing device and that rotates
the pump rotor, a motor rotor that is fixed to a motor housing-side
end portion of the motor shaft, and a motor stator that is fixed to
the motor housing, wherein the bearing device includes a first
bearing that is arranged in a closed-end hole formed in the pump
plate and that supports a pump housing-side end portion of the
motor shaft, and a second bearing that is arranged radially inward
of a cylindrical bearing support portion formed in the pump housing
and extending inside the motor housing, and that supports a middle
portion of the motor shaft, and wherein the pump rotor is arranged
between the first bearing and the second bearing.
2. The electric pump unit according to claim 1, wherein the first
bearing is a plain bearing.
3. The electric pump unit according to claim 1, wherein: the pump
rotor is formed of an outer gear and an inner gear; the inner gear
is fixed to the motor shaft with axial and radial movements of the
inner gear restricted; the second bearing is a rolling bearing that
includes an inner ring, an outer ring and rolling elements; and the
inner ring is fitted to a middle portion of the motor shaft by
interference fit.
4. The electric pump unit according to claim 2, wherein: the pump
rotor is formed of an outer gear and an inner gear; the inner gear
is fixed to the motor shaft with axial and radial movements of the
inner gear restricted; the second bearing is a rolling bearing that
includes an inner ring, an outer ring and rolling elements; and the
inner ring is fitted to a middle portion of the motor shaft by
interference fit.
5. The electric pump unit according to claim 3, wherein the outer
ring of the second bearing is fitted to the bearing support portion
by interference fit.
6. The electric pump unit according to claim 4, wherein the outer
ring of the second bearing is fitted to the bearing support portion
by interference fit.
7. The electric pump unit according to claim 3, wherein: the first
bearing is formed of a cylindrical metal member; the motor shaft is
fitted to the first bearing by clearance fit; the outer ring of the
second bearing is fitted to the bearing support portion by
clearance fit; and the motor shaft is fitted to the first bearing
such that an axis of the motor shaft is located closer to an oil
discharge port side than an axis of the cylindrical metal member
is.
8. The electric pump unit according to claim 4, wherein: the first
bearing is formed of a cylindrical metal member; the motor shaft is
fitted to the first bearing by clearance fit; the outer ring of the
second bearing is fitted to the bearing support portion by
clearance fit; and the motor shaft is fitted to the first bearing
such that an axis of the motor shaft is located closer to an oil
discharge port side than an axis of the cylindrical metal member
is.
Description
INCORPORATION BY REFERENCE
[0001] The disclosure of Japanese Patent Applications No.
2011-188291 filed on Aug. 31, 2011 and No. 2012-019831 filed on
Feb. 1, 2012 including the specification, drawings and abstract, is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to an electric pump unit that is used
as a hydraulic pump that supplies hydraulic pressure to, for
example, a transmission (speed change gear) of an automobile.
[0004] 2. Description of Related Art
[0005] Hydraulic pressure is supplied to a transmission of an
automobile by a hydraulic pump. In an automobile in which so-called
idle stop (idling stop) is performed, that is, an engine is
stopped, when the automobile is stopped in view of, for example,
energy saving, an electric hydraulic pump is used in order to
ensure supply of hydraulic pressure to the transmission even during
idle stop.
[0006] An electric hydraulic pump for a transmission of an
automobile is mounted in a limited space in a vehicle body.
Therefore, the electric hydraulic pump is required to be more
compact, and also required to be lighter in weight and lower in
cost. To fulfill such requirements, there is suggested an electric
pump unit in which a pump, an electric motor for driving the pump,
and a controller for the electric motor are assembled together in a
common unit housing (refer to, for example, Japanese Patent
Application Publication No. 2010-116914 (JP 2010-116914 A)).
[0007] In such a conventional electric pump unit, a motor housing
is coupled to a rear side portion of a pump body that constitutes a
pump, and an electric motor and a controller are accommodated in a
sealed motor chamber formed inside the motor housing. The electric
motor is arranged at the front side (the pump body side) inside the
motor chamber, and a substrate of the controller is fixed to a rear
end face of the electric motor. Further, a plurality of electrical
parts (electrical components and electronic components), such as
capacitors and FETs, that constitute the controller are mounted on
the substrate.
[0008] The electric motor includes a motor rotor and a motor
stator. The motor rotor is fixed to a free end portion at the rear
side of a pump drive motor shaft that is supported by a bearing
device. The motor stator is fixed to the motor housing. A pump
chamber is formed inside the pump body. The pump body has a
cylindrical bearing support portion that extends into the motor
housing, and the bearing device for the motor shaft is provided
inside the bearing support portion. The front portion of the motor
shaft enters the pump chamber, and a pump rotor of the pump is
fixed to a front-side free end portion of the motor shaft. When the
pump is an internal gear pump, an inner gear that is an inner pump
rotor is fixed to the front end portion of the motor shaft.
[0009] The bearing device includes two single-row deep groove ball
bearings that are arranged side-by-side in the axial direction. An
oil seal that seals a clearance between the pump chamber and the
bearing device is provided in the bearing support portion of the
pump body.
[0010] In the electric pump unit, two rolling bearings of the
bearing device are arranged adjacent to each other in order to
reduce the size of the electric pump unit. Thus, the motor shaft is
supported in a cantilever manner, that is, one end of the motor
shaft, on the motor rotor side, is supported, and the other end of
the motor shaft, on the pump rotor side, is a free end. In
addition, in order to reduce cost, each of the two rolling bearings
is formed of a single-row deep groove ball bearing. Furthermore, in
order to reduce assembly cost, the ball bearings are fitted to the
bearing support portion and the motor shaft by clearance fit.
[0011] When the pump is an internal gear pump, an oil suction port
and an oil discharge port are formed at symmetrical positions of
the pump housing, which correspond to a portion at which the inner
gear and an outer gear, which is an outer pump rotor, are in mesh
with each other.
[0012] In the above-described conventional electric pump unit,
during an operation of the pump, although the pressure in the oil
suction port of the pump chamber is low, the pressure in the oil
discharge port becomes high. Therefore, radial force acts on the
front end portion (pump housing-side end portion) of the motor
shaft to which the inner gear is fixed and which is supported in a
cantilever manner. As described above, the single-row deep groove
ball bearings, that is, the two rolling bearings of the bearing
device arranged side-by-side, are fitted by clearance fit.
Therefore, the bearing support stiffness is low, and the motor
shaft is inclined. Due to the inclination of the motor shaft, the
inner gear is inclined and rotates while being in contact with the
motor housing. Therefore, noise may occur, and abrasion may occur
in the motor rotor and the motor housing.
SUMMARY OF THE INVENTION
[0013] It is an object of the invention to provide an electric pump
unit in which the bearing support stiffness of a bearing device is
increased to reduce inclination of a motor shaft and a motor
rotor.
[0014] An aspect of the invention relates to an electric pump unit
that includes: a pump body of a pump that sucks in and discharges
fluid, wherein the pump body includes a pump housing and a pump
plate, the pump housing forms a pump chamber that accommodates a
pump rotor, and the pump plate is provided at one end of the pump
housing; a motor housing that is fixed to the other end of the pump
housing and that accommodates a pump driving electric motor; and
the electric motor that includes a motor shaft that is supported by
a bearing device and that rotates the pump rotor, a motor rotor
that is fixed to a motor housing-side end portion of the motor
shaft, and a motor stator that is fixed to the motor housing. The
bearing device includes a first bearing that is arranged in a
closed-end hole formed in the pump plate and that supports a pump
housing-side end portion of the motor shaft, and a second bearing
that is arranged radially inward of a cylindrical bearing support
portion formed in the pump housing and extending inside the motor
housing, and that supports a middle portion of the motor shaft. The
pump rotor is arranged between the first bearing and the second
bearing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Features, advantages, and technical and industrial
significance of exemplary embodiments of the invention will be
described below with reference to the accompanying drawings, in
which like numerals denote like elements, and wherein:
[0016] FIG. 1 is a longitudinal sectional view of main portions of
an electric pump unit according to a first embodiment of the
invention;
[0017] FIG. 2 is a longitudinal sectional view of main portions of
an electric pump unit according to a second embodiment of the
invention;
[0018] FIG. 3 is a longitudinal sectional view of main portions of
an electric pump unit according to a third embodiment of the
invention;
[0019] FIG. 4 is a view schematically showing an example of a
manner of assembling the electric pump unit in the first embodiment
of the invention;
[0020] FIG. 5A and FIG. 5B are views for illustrating the operation
and effect of the assembling manner shown in FIG. 4; and
[0021] FIG. 6A and FIG. 6B are views for illustrating a problem of
an assembling manner that is compared with the assembling manner
shown in FIG. 4.
DETAILED DESCRIPTION OF EMBODIMENTS
[0022] Hereinafter, an electric pump unit for a transmission of an
automobile according to embodiments of the invention will be
described with reference to the accompanying drawings. FIG. 1 is a
longitudinal sectional view of main portions of an electric pump
unit according to a first embodiment of the invention. In the
following description, the left side in FIG. 1 is defined as the
front side, and the right side in FIG. 1 is defined as the rear
side.
[0023] An electric pump unit 1 is formed by assembling a pump 3
that sucks in and discharges oil, a pump driving electric motor 4,
and a controller 5 for the electric motor 4 together in a unit
housing 2. In this example, the pump 3 is an internal gear pump,
and the motor 4 is a sensorless-controlled DC brushless motor that
has three-phase coils.
[0024] The unit housing 2 is formed of a pump body 6 of the pump 3
and a motor housing 7 that accommodates the electric motor 4 and
the controller 5.
[0025] The pump body 6 is formed of a pump housing 8 and a pump
plate 9 arranged in front of the pump housing 8. The pump housing 8
is formed in a thick plate member that extends in a direction
perpendicular to the front-rear direction, and has a pump chamber
10 at its center portion. The pump chamber 10 is open at its front
side.
[0026] The pump plate 9 is fixed to the front face of the pump
housing 8 via an O-ring 47 to close the front side of the pump
chamber 10. An outer gear 11 that serves as an outer pump rotor is
rotatably accommodated in the pump chamber 10. An inner gear 12
that serves as an inner pump rotor and that is in mesh with the
outer gear 11 is arranged radially inward of the outer gear 11. The
pump housing 8 and the pump plate 9 are made of, for example, an
aluminum alloy.
[0027] The motor housing 7 is formed of a cylindrical motor case 13
made of synthetic resin and a disc-shaped lid 14. The lid 14 is
fixed to the rear end of the motor case 13. The front end of the
motor case 13 is fixed to the rear face of the pump housing 8 via
an O-ring 48. The pump plate 9, the pump housing 8, and the motor
case 13 are fixed, at coupling portions 9a, 8a, 13a, to each other
with bolts 16. The coupling portions 9a, 8a, 13a are integrally
formed with the pump plate 9, the pump housing 8, and the motor
case 13 so as to protrude radially outward from the outer
peripheries of the pump plate 9, pump housing 8, and motor case 13,
respectively. The rear end opening of the motor case 13 is closed
by the lid 14.
[0028] The electric motor 4 has a motor shaft 18 that serves as a
pump drive shaft that extends in the front-rear direction. The
motor shaft 18 is supported by a bearing device 17. The bearing
device 17 is formed of a first bearing 21 and a second bearing 22.
The first bearing 21 supports the front end portion (pump
housing-side end portion) of the motor shaft 18. The second bearing
22 supports the motor shaft 18 at its middle portion in the
front-rear direction.
[0029] The second bearing 22 is formed of two deep groove ball
bearings 51, 52 that are arranged adjacent to each other in the
front-rear direction. Each of the deep groove ball bearings 51, 52
is a sealed type bearing with grease lubrication. The deep groove
ball bearing 51 includes an inner ring 51a, an outer ring 51b, a
plurality of balls (rolling elements) 51c, and a pair of seals 51d.
The deep groove ball bearing 52 includes an inner ring 52a, an
outer ring 52b, a plurality of balls (rolling elements) 52c, and a
pair of seals 52d.
[0030] The motor shaft 18 is formed in a stepped shape. The front
portion of the motor shaft 18 extends through the center portion of
the pump housing 8 and enters the pump chamber 10, and the front
end portion of the motor shaft 18 is fitted into a closed-end hole
9b formed in the rear face of the pump plate 9.
[0031] The first bearing 21 is formed of a cylindrical bushing
(cylindrical metal member), and is fixed to the closed-end hole 9b
formed in the rear face of the pump plate 9 by interference fit.
The front end portion of the motor shaft 18 is fitted into the
first bearing 21 by clearance fit. Thus, the inner periphery of the
first bearing 21 (bushing) and the outer periphery of the front end
portion of the motor shaft 18 are slidable with respect to each
other. Thus, the first bearing 21 constitutes a plain bearing.
[0032] A cylindrical bearing support portion 15 that is smaller in
diameter than the motor case 13 is integrally formed at the center
of the rear end face of the pump housing 8, and extends into the
motor case 13.
[0033] The inner rings 51a, 52a of the deep groove ball bearings
51, 52 are fitted to the motor shaft 18 by interference fit, and
the outer rings 51b, 52b of the deep groove ball bearings 51, 52
are fitted to the bearing support portion 15 by clearance fit.
[0034] An oil seal 20 is arranged between the second bearing 22 and
the inner gear 12. The oil seal 20 seals the clearance between the
bearing support portion 15 and the motor shaft 18.
[0035] The inner gear 12 is fitted to the motor shaft 18 at a
portion close to the front end portion of the motor shaft 18 by
interference fit so as to be in contact with the rear face of the
pump plate 9. Through the interference fit (press-fitting), the
inner gear 12 is fixed to the motor shaft 18 with its axial and
radial movements restricted.
[0036] A motor rotor 23 that constitutes the motor 4 is fixed to
the rear end portion (motor housing-side end portion) of the motor
shaft 18, which protrudes rearward from the bearing support portion
15. In the motor rotor 23, a permanent magnet support member 25
made of synthetic resin is fixedly provided at the outer peripheral
portion of a cylindrical rotor body 24 and segmented permanent
magnets 26 are supported at multiple portions of the support member
25, which are equiangularly aligned in the circumferential
direction.
[0037] A motor stator 27 that constitutes the motor 4 is fixed to
the inner periphery of the motor case 13, which faces the motor
rotor 23. In the stator 27, an insulator (synthetic resin
insulator) 29 is assembled to a stator core 28 made of laminated
steel sheets and coils 30 are wound around portions of the
insulator 29. In this example, the stator 27 is molded integrally
with the inner peripheral portion of the motor case 13.
[0038] The rotor body 24 is formed of a cylindrical portion 24a and
a flange 24b. The rotor body 24 has a U-shape in lateral cross
section. The cylindrical portion 24a faces the motor stator 27. The
flange 24b extends radially outward from the rear end of the motor
shaft 18, and is integrated with the cylindrical portion 24a.
[0039] A substrate 31 of the controller 5 is fixed to the rear end
of the insulator 29, and a component 32 that constitutes the
controller 5 is mounted on the substrate 31. FIG. 1 shows only one
component 32 that is mounted on the front face of the substrate 31.
However, a component is arranged at a predetermined position of at
least one of the front face and rear face of the substrate 31. The
component 32 shown in FIG. 1 is, for example, an electrolytic
capacitor.
[0040] In the stator core 28, pole portions (teeth) 28b that
protrude radially inward are integrally formed at multiple portions
of the inner periphery of an annular portion 28, which are aligned
equiangularly in the circumferential direction. The distal end
portion of each pole portion 28b extends on both sides in the
circumferential direction, and the inner peripheries of the pole
portions 28b form a single cylindrical face.
[0041] The insulator 29 is formed of a pair of front and rear
halves 33, 34. Each of the halves 33, 34 is molded from synthetic
resin, such as polyphenylene sulfide (PPS) resin. The halves 33, 34
are assembled to the stator core 28 from the front side and the
rear side so as to cover the surface of the stator core 28, other
than the outer periphery of the annular portion 28a and the inner
peripheries of the pole portions 28b. The halves 33, 34
respectively have coil fitting portions 33a, 34a that cover
portions of the stator core 28, other than the inner peripheries of
the pole portions 28b. At each of the pole portions 28b of the
stator core 28, the coil 30 is wound around a portion covered with
the coil fitting portions 33a, 34a of the halves 33, 34. Substrate
mounting protruding portions 34b that extend rearward are
integrally formed at multiple portions of the rear half 34, which
are located radially outward of the coil fitting portion 34a and
which are equiangularly aligned in the circumferential direction. A
metal internal thread member 35 is embedded inside the rear end
portion of each protruding portion 34b. An internal thread is
formed on the inner periphery of each metal internal thread member
35.
[0042] The motor case 13 is integrated with the stator 27 by
molding synthetic resin, such as polyamide 66 (PA66), at the outer
peripheral portion of the stator 27 using a die. The surface of the
stator 27, other than the inner peripheries of the pole portions
28b of the stator core 28, the inner peripheries of the coil
fitting portions 33a, 34a of the insulator 29 and the rear end
faces of the protruding portions 34b, are covered with the motor
case 13. A connector 37 provided with a plurality of pins 36 is
integrally formed with the outer periphery of the motor case
13.
[0043] The lid 14 is made of synthetic resin, and is fixed to the
rear end of the motor case 13 by an appropriate method, such as
thermal welding.
[0044] The substrate 31 of the controller 5 is fixed to the
insulator 29 by screws 39 that are screwed to the internal thread
members 35 at the protruding portions 34b of the insulator 29.
Although not shown in the drawing, a plurality of bus bars is
assembled to a molded body formed of the insulator 29 and the motor
case 13, and the coils 30 of the stator 27 are electrically
connected to each other and electrically connected to the substrate
31 via the bus bars. The pins 36 of the connector 37 are also
electrically connected to the substrate 31.
[0045] Oil suction ports 40, 41 are respectively formed in the
walls of the pump housing 8 and the pump plate 9, which face each
other and which correspond to a meshing portion (in this example, a
lower-side meshing portion) at which the inner gear 12 and the
outer gear 11 of the pump 3 are in mesh with each other. Oil
discharge ports 42, 43 are respectively formed in the walls of the
pump housing 8 and the pump plate 9, which face each other and
which correspond to a meshing portion (in this example, upper-side
meshing portion) at which the inner gear 12 and outer gear 11 of
the pump 3 are in mesh with each other. The pump plate 9 has an oil
suction hole 44 and an oil discharge hole 45. The oil suction hole
44 is in communication with the oil suction port 41. The oil
discharge hole 45 is in communication with the oil discharge port
43. The wall of the pump housing 8, which faces the pump chamber
10, has an oil release groove 46. The oil release groove 46
provides communication between a hole 19, through which the motor
shaft 18 is passed, and the oil suction port 40.
[0046] When the pump 3 is driven by the electric motor 4 and the
inner gear 12 and the outer gear 11 rotate, the pressure in the oil
suction ports 40, 41 is low, and the pressure in the oil discharge
ports 42, 43 is high. Therefore, the inner gear 12 receives radial
(in this example, downward) force.
[0047] In the above embodiment, the middle portion of the motor
shaft 18 in the front-rear direction is supported by the second
bearing 22, and the front end portion of the motor shaft 18 is
supported by the first bearing 21. Therefore, the bearing support
stiffness improves, and, even when radial force due to hydraulic
pressure acts on the inner gear 12, inclination of the motor shaft
18 is prevented. As a result, it is possible to suppress slanting
of the pump 3, and to reduce noise and abrasion.
[0048] In addition, because the first bearing 21 is a plain bearing
such as a bushing, it is possible to install the first bearing 21
in a small space, and to easily ensure sites for the oil suction
port 41, the oil discharge port 43, the oil suction hole 44, the
oil discharge hole 45, and the like, in the pump plate 9.
[0049] In addition, because the inner gear 12 is fitted to the
motor shaft 18 by interference fit, axial movement of the motor
shaft 18 is restricted to suppress a backlash. Therefore, the outer
rings 51b, 52b of the deep groove ball bearings 51, 52 may be
fitted to the bearing support portion 15 by clearance fit, and no
circlip needs to be provided between the outer rings 51b, 52b.
Therefore, it is easy to fit the bearings 51, 52, and efficiency of
assembly improves. However, in order to further improve the bearing
support stiffness, the outer rings 51b, 52b of the deep groove ball
bearings 51, 52 may be fitted to the bearing support portion 15 by
interference fit.
[0050] FIG. 2 is a longitudinal sectional view of main portions of
an electric pump unit according to a second embodiment of the
invention. The second embodiment differs from the first embodiment
in the configuration of a rotary portion including a bearing
device. Hereinafter, the same components as those in the first
embodiment will be denoted by the same reference numerals as those
in the first embodiment, and the description thereof is
omitted.
[0051] In the present embodiment, a bearing device 61 that supports
a motor shaft 60 of the electric motor 4 is formed of a first
bearing 63 and a second bearing 64. The second bearing 64 supports
the motor shaft 60 at its middle portion in the front-rear
direction. The first bearing 63 supports the front end portion of
the motor shaft 60. The first bearing 63 is a bushing as in the
case of the first embodiment. The second bearing 64 is a single
deep groove ball bearing.
[0052] The motor shaft 60 is formed in a circular columnar shape,
unlike the first embodiment in which the motor shaft is formed in a
stepped shape. In addition, the axial length of the motor shaft 60
is shorter than that in the first embodiment because the second
bearing 64 is formed of the single deep groove ball bearing.
[0053] A bearing support portion 62 that is integrally formed with
the pump housing 8 is formed of a thick portion 62a and a thin
portion 62b that is located behind the thick portion 62a. The thick
portion 62a is smaller in inside diameter and larger in outside
diameter than the thin portion 62b. An inward flange 62c is
provided on the inner periphery at the boundary between the thick
portion 62a and the thin portion 62b.
[0054] The second bearing 64 is arranged on the inner periphery of
the thick portion 62a, and an oil seal 65 is arranged on the inner
periphery of the thin portion 62b. The oil seal 65 seals the
clearance between the bearing support portion 62 and the motor
shaft 60. The interference of the oil seal 65 is slightly smaller
than that in the first embodiment.
[0055] The second bearing 64 is arranged such that an inner gear 12
(pump rotor) is interposed between the second bearing 64 and the
first bearing 63. The second bearing 64 is an open-type deep groove
ball bearing that has an inner ring 64a, an outer ring 64b, and a
plurality of balls (rolling elements) 64c. The inner ring 64a is
fitted to the middle portion of the motor shaft 60 by interference
fit, and the outer ring 64b is fitted to the thick portion 62a of
the bearing support portion 62 by interference fit.
[0056] A front end-side portion of the motor shaft 60 is coupled to
the inner gear 12 by a dowel pin 66. The dowel pin 66 is a coupling
member for coupling the motor shaft 60 to the inner gear 12 such
that the motor shaft 60 and the inner gear 12 rotate together with
each other and do not move relative to each other in the axial
direction. Thus, the inner gear 12 is fixed to the motor shaft 60
with its axial and radial movements restricted. The coupling member
may be a pin, such as a spiral pin, or a key, instead of the dowel
pin 66.
[0057] A motor rotor 67 is fixed to the rear end portion (motor
housing-side end portion) of the motor shaft 60. The motor stator
27 is provided at the same position as that in the first
embodiment. A rotor body 68 of the motor rotor 67 is formed of a
cylindrical portion 68a and a flange 68b. The cylindrical portion
68a faces the motor stator 27. The flange 68b extends radially
outward from the rear end of the motor shaft 61, and is integrated
with the cylindrical portion 68a. Because the axial length of the
motor shaft 60 is shorter than that in the first embodiment, the
rotor body 68 is formed in a shape (the lateral sectional shape is
an 1-shape) in which the flange 68b is fixed to substantially the
center of the cylindrical portion 68a in the axial direction.
[0058] In this second embodiment as well as in the first
embodiment, the middle portion of the motor shaft 60 in the
front-rear direction is supported by the second bearing 64, and the
front end portion of the motor shaft 60 is supported by the first
bearing 63. Thus, the bearing support stiffness improves, and, even
when radial force due to hydraulic pressure acts on the inner gear
12, inclination of the motor shaft 60 is prevented. Thus, it is
possible to suppress slanting of the pump 3, and to reduce noise
and abrasion. In addition, because the inner ring 64a and the outer
ring 64b of the second bearing 64 are fitted by interference fit,
the bearing support stiffness is further improved.
[0059] In addition, because the motor shaft 60 and the inner gear
12 are coupled to each other by the dowel pin 66, axial movement of
the motor shaft 60 is restricted to suppress a backlash.
[0060] In addition, because the flange 68b of the rotor body 68 is
fixed to substantially the center portion of the cylindrical
portion 68a in the axial direction, the rotor body 68 is
well-balanced in comparison with the rotor body 24 in the first
embodiment in which the flange 24b is fixed to the rear end portion
of the cylindrical portion 24a. As a result, it is possible to
prevent runout of the motor rotor 67.
[0061] The rear portion of the bearing support portion 62 is the
thin portion 62b in order to avoid contact with the motor rotor 67.
Further, the front portion that does not contact the motor rotor 67
is the thick portion 62a. Because the outer ring 64b of the second
bearing 64 is fitted to the thick portion 62a by interference fit,
it is possible to sufficiently provide interference between the
bearing support portion 62 and the outer ring 64b. Thus, no
additional slipping prevention measures (such as prevention of
axial movement using a circlip) need to be taken. In addition,
because stiffness increases owing to the inward flange 62c,
deformation of the bearing support portion 62 at the time of
press-fitting of the oil seal 65 is prevented, and interference is
stable.
[0062] FIG. 3 is a longitudinal sectional view of main portions of
an electric pump unit according to a third embodiment of the
invention. The third embodiment differs from the second embodiment
in the configuration of a bearing device including an oil seal.
Hereinafter, the same components as those in the first and second
embodiments will be denoted by the same reference numerals as those
in the first and second embodiments, and the description thereof is
omitted.
[0063] A bearing device 71 according to the present embodiment is
formed of a first bearing 73 and a second bearing 74, as in the
case of the first and second embodiments.
[0064] A bearing support portion 72 that is integrally formed with
the pump housing 8 is formed of a thick portion 72a and a thin
portion 72b located behind the thick portion 72a. The thick portion
72a is equal in inside diameter to the thin portion 72b and is
larger in outside diameter than the thin portion 72b. An inward
flange 72c is provided at the front end portion of the thick
portion 72a. An oil seal 75 is arranged radially inward of the
thick portion 72a, and the second bearing 74 is arranged radially
inward of the thin portion 72b.
[0065] The first bearing 73 is a bushing, as in the cases of the
first and second embodiments. The second bearing 74 is a sealed
type deep groove ball bearing with grease lubrication, and includes
an inner ring 74a, an outer ring 74b, a plurality of balls (rolling
elements) 74c, and a pair of seals 74d.
[0066] The second bearing 74 is arranged such that an inner gear 12
(pump rotor) and the oil seal 75 are interposed between the second
bearing 74 and the first bearing 73. The second bearing 74 is
arranged such that the inner ring 74a is fitted to the middle
portion of the motor shaft 60 by interference fit and the outer
ring 74b is fitted to the thin portion 72b of the bearing support
portion 72 by interference fit.
[0067] In the third embodiment, the positional relationship between
the oil seal 75 and the second bearing 74 is inverted from that in
the second embodiment. Thus, the second bearing 74 is arranged near
the rear end portion of the motor shaft 60 and, as compared with
the second embodiment, the distance between the first bearing 73
and the second bearing 74 is increased. Thus, the bearing support
stiffness is further improved.
[0068] As in the case of the second embodiment, the lateral
sectional shape of the motor rotor 67 is an I-shape. This shape is
effective in preventing runout of the motor rotor 67.
[0069] In the first embodiment described above, the outer rings
51b, 52b of the two deep groove ball bearings 51, 52 that
constitute the second bearing 22 are fitted to the bearing support
portion 15 of the pump housing 8 by clearance fit. In addition, the
front end portion of the motor shaft 18 is fitted into the first
bearing 21 by clearance fit. An example of the assembling manner in
this case is shown in FIG. 4.
[0070] In FIG. 4, the assembly is performed such that an axis 18a
of the motor shaft 18 is closer to the oil discharge port side than
an axis 21a of the first bearing 21 is. Note that, although the
clearance formed by the clearance fit is actually approximately
several tens of .mu.m (e.g. approximately 20 .mu.m on the first
bearing 21 side, and approximately 10 .mu.m on the second bearing
22 side), the clearance is schematically illustrated in an
exaggerated manner in FIG. 4.
[0071] The assembly is usually performed such that the axis 21a of
the first bearing 21 coincides with the axis 18a of the motor shaft
18 and therefore the front end portion of the motor shaft 18 is
located at the middle between the oil suction port 41 and the oil
discharge port 43, as shown in FIG. 6A. In contrast to this,
according to the present embodiment, as shown in FIG. 4 and FIG.
5A, the assembly is performed such that the front end portion of
the motor shaft 18 is located closer to the oil discharge port side
than to the oil suction port side. In this way, the hydraulic
pressure on the oil suction port side becomes lower than the
hydraulic pressure on the oil discharge port side when the
hydraulic pressure is applied, and the clearance on the oil suction
port side is larger than the clearance on the oil discharge port
side before the hydraulic pressure is applied.
[0072] The pump 3 of the electric pump unit 1 according to the
invention is a pump that operates when a vehicle is placed in
idling stop and an engine is stopped. Therefore, when the pump 3 is
operating, the other parts are at a standstill. Accordingly, if the
acoustic pressure of the noise generated from the pump 3 is high, a
driver may feel uncomfortable. Therefore, it is necessary to reduce
the level of noise that is generated from the pump 3.
[0073] If the assembly is performed as shown in FIG. 6A, the axis
18a of the motor shaft 18 and the axis 21a of the first bearing 21
coincide with each other when the hydraulic pressure is not
applied. When the hydraulic pressure is applied, the hydraulic
pressure on the oil discharge port side becomes high, and
therefore, the front end portion of the motor shaft 18 is pushed
toward the oil suction port side as shown in FIG. 6B. Thus, the
motor shaft 18 may slide over the first bearing 21 on the oil
suction port side. The sliding noise may increase the low-frequency
(281 to 2245 Hz) acoustic pressure.
[0074] In contrast to this, if the assembly is performed as shown
in FIG. 5A, the axis 18a of the motor shaft 18 is already located
closer to the oil discharge port side than to the oil suction port
side when the hydraulic pressure is not applied. When the hydraulic
pressure is applied, the hydraulic pressure becomes high on the oil
discharge port side. Therefore, as shown in FIG. 5B, the front end
portion of the motor shaft 18 is pushed toward the oil suction port
side. At this time, the clearance on the oil discharge port side,
which has been small, is increased. If the clearance is equal to or
larger than 10 .mu.m, an oil film is formed between the motor shaft
18 and the first bearing 21 and therefore the motor shaft 18
rotates without being in friction contact with the first bearing
21. In this way, it is possible to reduce the low frequency (281 to
2245 Hz) acoustic pressure due to the sliding noise between the
motor shaft 18 and the first bearing 21.
[0075] In order to obtain a clearance as shown in FIG. 5A, the
motor shaft 18 may be brought closer to the oil discharge port side
by applying a load of, for example, 5 to 30N to the motor shaft
18.
[0076] By performing the assembly as described above, it is
possible to reduce the low-frequency acoustic pressure, and it is
possible to suppress fluctuation of the acoustic pressure by
reducing the variations of the assembled position. Further, it is
possible to improve the durability by reducing occurrence of the
friction contact between the first bearing 21 and the motor shaft
18.
[0077] In the above embodiments, the first bearings 21, 63, 73 of
the bearing devices 17, 61, 71 are bushings that serve as plain
bearings, and the second bearings 22, 64, 74 are formed of deep
groove ball bearings. However, the invention is not limited to this
configuration. The first bearing may be a rolling bearing, and the
second bearing may be a rolling bearing other than a deep groove
ball bearing. When the first bearing is a rolling bearing, the
first bearing is desirably formed of a needle roller bearing. The
needle roller bearing, for example, includes a cylindrical outer
ring, a plurality of needle rollers arranged along the bore surface
of the outer ring and a cage that retains the plurality of needle
rollers. The outer ring is fixedly press-fitted to the peripheral
wall of the closed-end hole 9b. If the first bearing is formed of a
needle roller bearing instead of a ball bearing, it is possible to
easily ensure sufficient assembling efficiency and sufficient space
for ports even when the rolling bearing is used.
[0078] The overall configuration of the electric pump unit and the
configuration of the portions of the electric pump unit are not
limited to those in the above-described embodiments, and may be
modified as needed.
[0079] In addition, the invention may also be applied to an
electric pump unit other than an electric pump unit for a
transmission.
[0080] With the electric pump unit according to the invention, it
is possible to increase the bearing support stiffness of the
bearing device to thereby reduce inclination of the motor shaft and
inclination of the pump rotor.
* * * * *