U.S. patent application number 15/047197 was filed with the patent office on 2016-08-25 for electric oil pump.
The applicant listed for this patent is Hitachi Automotive Systems, Ltd.. Invention is credited to Takayuki CHIKAOKA.
Application Number | 20160245283 15/047197 |
Document ID | / |
Family ID | 56577721 |
Filed Date | 2016-08-25 |
United States Patent
Application |
20160245283 |
Kind Code |
A1 |
CHIKAOKA; Takayuki |
August 25, 2016 |
Electric Oil Pump
Abstract
An electric oil pump is provided to including: (i) a pump part
housed in a pump part-accommodating portion formed in a metal pump
housing; (ii) an electric motor part housed in an electric motor
part-accommodating portion formed in the pump housing; and (iii) a
drive control part having (a) a control part case fastened to the
pump housing and formed of synthetic resin, (b) a control board for
supplying a driving current to the electric motor part, and (c) a
metal control part cover fastened to the control part case and
accommodating the control board. In this pump, the control part
cover and the pump housing are covered with an oxide film having
corrosion resistance and heat resistance at least at their outer
surface, and the pump housing provided with the oxide film is fixed
to an automatic transmission casing in a manner to be immersed in a
hydraulic oil.
Inventors: |
CHIKAOKA; Takayuki;
(Isesaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi Automotive Systems, Ltd. |
Hitachinaka-shi |
|
JP |
|
|
Family ID: |
56577721 |
Appl. No.: |
15/047197 |
Filed: |
February 18, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04C 2/086 20130101;
F04C 2/102 20130101; F04C 13/008 20130101; F04C 2280/04 20130101;
F04C 15/0096 20130101; F04C 2230/92 20130101; F04C 2240/808
20130101 |
International
Class: |
F04C 15/00 20060101
F04C015/00; F04C 2/10 20060101 F04C002/10; F04C 2/08 20060101
F04C002/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 2015 |
JP |
2015-030113 |
Claims
1. An electric oil pump comprising: a pump part housed in a pump
part-accommodating portion formed in a metal pump housing; an
electric motor part housed in an electric motor part-accommodating
portion formed in the pump housing; and a drive control part
comprising: a control part case fastened to the pump housing and
formed of synthetic resin; a control board for supplying a driving
current to the electric motor part; and a metal control part cover
fastened to the control part case and accommodating the control
board, wherein the pump housing is fixed to a casing of an
automatic transmission in a manner to be immersed in a hydraulic
oil, and wherein the control part cover and the pump housing are
covered with an oxide film having corrosion resistance and heat
resistance at least at their outer surface, and the pump housing
provided with the oxide film is fixed to the casing of the
automatic transmission in a manner to be immersed in the hydraulic
oil.
2. An electric oil pump as claimed in claim 1, wherein the pump
housing and the control part cover are formed of aluminum alloy,
and the oxide film comprises aluminum oxide and formed on the outer
surface of the pump housing and the outer surface of the control
part cover by anodic oxidation treatment.
3. An electric oil pump as claimed in claim 2, wherein the oxide
film comprising aluminum oxide is subjected to sealing treatment.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to improvements in an electric oil
pump, and more particularly to improvements in an electric oil pump
where a drive control part which can supply a driving current to an
electric motor part for rotating a pump rotor is disposed adjacent
to the electric motor part.
[0002] In recent years, there have been proposed and developed
various idling-stop system equipped vehicles or automatic engine
stop-restart system equipped hybrid vehicles for improved fuel
economy. In these vehicles, pumps driven by an internal combustion
engine are to stop at the time when the internal combustion engine
is stopped, and therefore the presence of a pump-driving source
other than the internal combustion engine is needed. In particular,
the idling-stop system equipped vehicles, automatic engine
stop-restart system equipped hybrid vehicles and the like require
an oil pump so that a hydraulic mechanism for controlling an
automatic transmission can keep ensuring a hydraulic pressure. In
view of the above, there has been developed the trend toward the
increase of the use of an electric oil pump which imparts a
rotational force to a pump rotor by using an electric motor to
cause pumping actions.
[0003] As an electric oil pump mounted to an automatic transmission
of an automotive vehicle, there has widely been adopted an internal
gear pump of a trochoid type. In an internal gear pump, a pump
rotor is rotated by a driving rotational shaft driven by a motor,
so that an outer rotor having an inner tooth engageable with an
outer tooth of the pump rotor is rotated. With this, the volume of
a plurality of volume chambers formed between the inner tooth of
the outer rotor and the outer tooth of the pump rotor is
continuously changed thereby performing intake/discharge of a
hydraulic oil. Such an internal gear pump is disclosed in Japanese
Patent Application Publication No. 2012-207638 (Patent Document 1)
for example.
[0004] A typical electric oil pump is provided including: a drive
control part for controlling the passage of electric current
through an electric motor; a stator section having a wire and iron
core for generating magnetomotive force by the electric current
passage from the drive control part; a rotor section disposed in a
space defined by the inner periphery of the stator section and
having a permanent magnet to be rotated by the magnetomotive force;
and a driving rotational shaft fixed to the rotor section by means
of press-fitting or the like so as to rotate together
therewith.
[0005] Moreover, in the recent electric oil pump, the drive control
part for running a controlled driving current into the wire portion
is getting fixed integral with the electric oil pump. The reason to
provide the drive control part integral with the electric oil pump
as mentioned above is for at least one or more purposes of:
shortening the length of wiring between the wire portion and the
drive control part to reduce the adverse effect of outside noise as
much as possible; decreasing a wiring cost; facilitating
calibration between the drive control part and a pump part;
improving handling property; and the like.
[0006] The above-discussed drive control part is provided composed
of: a control part case fastened to the side of the electric motor
part and formed of synthetic resin; a control part cover formed of
metal and so fixed as to enclose the control part case; and a
control board housed in a space defined between the control part
case and the control part cover. The reason to employ a control
part cover formed of metal as mentioned above is for letting the
cover function as a heat sink which can dissipate heat generated
from the control board to the outside. Since the control board is
equipped with an inverter circuit, a large amount of heat is
generated from a switching element comprised of MOSFET that
constitutes the inverter circuit. In order to dissipate the heat, a
control part cover formed of metal is employed.
[0007] The components of the electric motor part and those of the
pump part are accommodated in a pump housing, and the
above-mentioned control part case formed of synthetic resin is
fastened to the pump housing. The pump housing is formed of metal
and fastened to an automatic transmission casing with a fastening
bolt. Furthermore, the control part cover and the pump housing,
which are formed of metal are electrically connected with each
other through a fastening bolt formed of metal, while the automatic
transmission casing and the pump housing are also electrically
connected with each other by a fastening bolt formed of metal. The
reason to make such an arrangement is for letting static
electricity escape toward the side of the automatic transmission,
because static electricity charged on the control part case or the
control part cover can adversely affect an electric element of the
control board.
[0008] Patent Document 1: Japanese Patent Application Publication
No. 2012-207638
SUMMARY OF THE INVENTION
[0009] However, drawbacks have been encountered in the above
discussed conventional oil cooler. More specifically, this kind of
electric oil pump is usually mounted inside an engine compartment
of an automotive vehicle, so that its metal portions are liable to
corrosion due to rainwater or saltwater intruding into the engine
compartment. In particular, corrosion tends to develop at a contact
surface between a control part case and a control part cover and a
contact surface between the control part case and a pump housing
thereby allowing the intrusion of rainwater or saltwater also into
a space accommodating a control board and into the electric motor
part in due course. Hence there is a fear that the electric element
on the control board and the wire in the electric motor part cause
a short to be broken down.
[0010] Additionally, the pump housing is formed of aluminum or
aluminum alloy, and mounted in such a manner as to reside in the
interior of the automatic transmission to be immersed in a
hydraulic oil. The reason why the pump housing is mounted in the
interior of the automatic transmission is in order to reduce the
automatic transmission in axial length or outer dimension itself as
much as possible. Additionally, the pump housing is to be exposed
to the hydraulic oil, and therefore formed of aluminum or aluminum
alloy. For example, if the pump housing is formed of synthetic
resin, the synthetic resin is to swell up by the hydraulic oil so
that the pump housing cannot keep its functions.
[0011] Though the pump housing is formed of aluminum or aluminum
alloy as discussed above, the temperature of the hydraulic oil gets
increased as an automotive vehicle travels, and the heat of the
hydraulic oil is to be transmitted to the drive control part
through such a well-thermal conductive pump housing. Consequently,
there arises a fear that the drive control part cannot be normally
operated by the influence of the heat.
[0012] An object of the present invention is to provide a novel and
improved electric oil pump which can prevent a space housing a
control board and an electric motor part from water intrusion while
inhibiting the heat of the hydraulic oil from transmitting to the
drive control part.
[0013] An aspect of the present invention resides in an electric
oil pump comprising: (i) a pump part housed in a pump
part-accommodating portion formed in a metal pump housing; (ii) an
electric motor part housed in an electric motor part-accommodating
portion formed in the pump housing; and (iii) a drive control part
comprising (a) a control part case fastened to the pump housing and
formed of synthetic resin, (b) a control board for supplying a
driving current to the electric motor part, and (c) a metal control
part cover fastened to the control part case and accommodating the
control board, wherein the pump housing is fixed to a casing of an
automatic transmission in a manner to be immersed in a hydraulic
oil, and wherein the control part cover and the pump housing are
covered with an oxide film having corrosion resistance and heat
resistance at least at their outer surface, and the pump housing
provided with the oxide film is fixed to the casing of the
automatic transmission in a manner to be immersed in the hydraulic
oil.
[0014] According to the present invention, an oxide film having
corrosion resistance and heat resistance is formed at least on the
outer surface of the control part cover (formed of metal) and the
outer surface of the pump housing (also formed of metal); with
this, interfaces among the control part cover, a control part case
and the pump housing are protected from corrosion. Moreover, since
the outer surface of the pump housing to be exposed to the
hydraulic oil is covered with the oxide film having corrosion
resistance and heat resistance, the pump housing is so improved in
heat resistance as to inhibit a drive control part from receiving
the influence of the heat of the hydraulic oil.
BRIEF DESCRIPTION OF THE DRAWING
[0015] FIG. 1 is an overall perspective view of an embodiment of an
electric oil pump according to the present invention;
[0016] FIG. 2 is a vertical cross-sectional view of the electric
oil pump of FIG. 1;
[0017] FIG. 3 is an exploded perspective view of the electric oil
pump of FIG. 1; and
[0018] FIG. 4 is a cross-sectional view of fixing parts among a
control part cover, a control part case and a pump housing.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Referring now to the accompanying drawings, an embodiment of
an electric oil pump according to the present invention will
specifically be discussed; however, the invention is not limited to
the illustrated embodiment, and modifications and variations of the
illustrated embodiment will occur to those skilled in the art.
[0020] An electric oil pump is, for example, a pump to be mounded
for automatic transmission of a vehicle having an idle stop
function. The automatic transmission refers to a belt-type
continuously variable transmission (hereinafter referred to as CVT)
equipped separately with a mechanical pump driven by an engine. In
the embodiment of the present invention, the electric oil pump is
used as a hydraulic pressure supply source for automatic
transmission and therefore fixed to a casing for automatic
transmission.
[0021] At the time of stopping the engine under an idle stop
control, the mechanical pump cannot ensure a hydraulic pressure.
Additionally, if a hydraulic pressure is reduced by, for example, a
leak from a friction fastening element or a pulley in the belt-type
CVT, a certain period of time is required for ensuring a hydraulic
pressure necessary for a restart so as to cause an drivability
deterioration. In view of the above, an electric oil pump capable
of discharging a hydraulic pressure regardless of the running state
of the engine is provided in addition to the mechanical pump to
ensure such an amount of a hydraulic pressure as to compensate for
the leak from the friction fastening element or the pulley, thereby
improving the drivability at the time of running the engine and at
the time of restarting the vehicle.
[0022] FIG. 1 is a perspective view of an electric oil pump,
showing an overall configuration thereof. FIG. 2 is a
cross-sectional view of the electric oil pump of FIG. 1. Electric
oil pump 10 is constructed from electric motor part 10A, drive
control part 10B fixed adjacent to electric motor part 10A, and
pump part 10C driven by electric motor part 10A. Incidentally, the
members illustrated in FIG. 1 other than these parts will be
explained with reference to FIGS. 2 and 3.
[0023] Electric motor part 10A is provided including at least rotor
section 16 and stator section 18 as shown in FIGS. 2 and 3, and
enclosed in electric motor part-accommodating portion 24 provided
to one side of metal pump housing 20 formed of aluminum alloy or
the like.
[0024] Additionally, the above-mentioned pump housing 20 is formed
having, at the other side, pump part-accommodating portion 22 which
can accommodate pump part 10C. Pump part 10C is composed of at
least pump rotor 12 having an external gear, and outer rotor 14
having an internal gear. Pump rotor 12 and outer rotor 14 are
housed in the above-mentioned pump part-accommodating portion 22
provided at the other side of pump housing 20. Drive control part
10B is constituted of at least control part case 44, control board
46 accommodated in control part case 44, and control part cover 48
to be fixed onto control part case 44 to enclose control board
46.
[0025] Pump cover 34 constituting pump part 10C is fastened to pump
housing 20 with fastening bolt (or pump cover-fastening bolt) 60A.
Likewise, control part case 44 and control part cover 48, which are
constituting drive control part 10B, are jointly fastened to pump
housing 20 at the side close to electric motor part 10A with
fastening bolt (or control part case-fastening bolt) 62A. More
specifically, control part case 44 and control part cover 48 are
jointly fastened, at least at one point, to pump housing 20 with
fastening bolt 62A. Furthermore, control part case 44 and control
part cover 48 are fastened to each other at five points with
fastening bolts (or control part cover-fastening bolts) 64A.
[0026] The structure of electric oil pump 10 will be explained in
detail by reference to FIG. 2. Electric oil pump 10 is provided to
include: pump part 10C composed of pump rotor 12 having an external
gear and outer rotor 14 having an internal gear; and electric motor
10A composed of rotor section 16 joined with pump rotor 12 and
stator section 18. Stator section 18 is wound with wire 18A, and an
end of the wire 18A is drawn into drive control part 42.
[0027] Pump part 10C and electric motor 10A are housed in electric
motor part-accommodating portion 24 provided at one end surface of
pump housing 20 and pump part-accommodating portion 22 provided at
the other end surface of pump housing 20, respectively. More
specifically, the pump housing 20 is formed having: pump
part-accommodating portion 22 which can accommodate outer rotor 14
rotatably therein at the side of the other end surface; electric
motor part-accommodating portion 24 which can support stator
section 18 fixedly at its inner periphery and at its opening
defined at the one end surface while accommodating rotor section 16
and the like therein; and bracket 26 axially outside the electric
motor part-accommodating portion 24, the bracket 26 being
attachable to automatic transmission casing 52. Incidentally, pump
housing 20 is a metal product formed of aluminum alloy.
[0028] The above-mentioned pump housing 20 is mounted in such a
manner as to reside in the interior of the automatic transmission
to be immersed in a hydraulic oil. The reason why pump housing 20
is mounted in the interior of the automatic transmission is in
order to reduce the automatic transmission in axial length or outer
dimension itself as much as possible. Additionally, pump housing 20
is formed of aluminum or aluminum alloy because it is to be exposed
to the hydraulic oil. If pump housing 20 is formed of synthetic
resin, the synthetic resin is to swell up by the hydraulic oil so
that pump housing 20 cannot keep its functions. This is the reason
why pump housing 20 is formed of aluminum or aluminum alloy.
[0029] As shown in FIG. 2, automatic transmission casing 52 is
formed with pump-accepting recess CA in its interior. In the state
where pump housing 20 is accommodated in the pump-accepting recess
CA, the outer periphery of pump housing 20 is filled with the
hydraulic oil. The hydraulic oil is adapted to circulate by the
pumping action.
[0030] On the upper surface of the fixing bracket 26 formed as a
part of pump housing 20, control part case-fixing section 54 formed
as a part of control part case 44 is mounted. The control part
case-fixing section 54 is pierced with metal bush 56 the both ends
of which are annularly opening, by insert molding. Fastening bolt
58A is provided to pierce bush 56 and fixing bracket 26 and then
screwed into automatic transmission casing 52, thereby fastening
electric oil pump 10 to automatic transmission casing 52. A similar
bracket is also provided at two other positions of pump housing 20,
though not shown, thereby fastening electric oil pump 10 to
automatic transmission casing 52 by the same structure.
[0031] Inside pump housing 20, there is provided a bearing portion
30 for rotatably supporting driving rotational shaft 28 which
connects pump rotor 12 to rotor section 16. This bearing portion 30
takes on such an arrangement that the inner peripheral surface
thereof rotatably supports the outer peripheral surface of the
medial region of driving rotational shaft 28. Incidentally, the
medial region refers to a region between pump rotor 12 and rotor
section 16 and therefore not limited to the midpoint of driving
rotational shaft 28.
[0032] Moreover, bearing portion 30 is formed at bulkhead 31
provided for dividing pump part-accommodating portion 22 and
electric motor part-accommodating portion 24 from each other. The
bearing portion 30 is the so-called plain bearing and formed with a
certain length of crevice between the inner peripheral surface of
bearing portion 30 and the outer peripheral surface of driving
rotational shaft 28. A hydraulic oil on the discharge side (or the
higher pressure side) is adapted to be introduced into this crevice
through oil introduction passage 33. Furthermore, seal member 32
for sealing driving rotational shaft 28 is provided on the upper
side of driving rotational shaft 28 and bearing portion 30.
[0033] Pump cover 34 is provided with: discharge port 36
cylindrically prolonged to communicate with an outlet of pump part
10C; and intake port 38 communicating with an inlet of pump part
10C. Seal ring 40 is attached to the tip end of the outer periphery
of discharge port 36.
[0034] Control part case 44 constituting drive control part 42 is
fixed onto pump housing 20 at the side of electric motor
part-accommodating portion 24 in a manner to enclose electric motor
part-accommodating portion 24. Incidentally, drive control part 42
as shown in FIG. 2 and drive control part 10B as shown in FIG. 1
are the same, though their reference numerals are different.
[0035] Drive control part 42 is constituted of: control part case
44 attached to pump housing 20 and formed of synthetic resin;
control board 46 accommodated in control part case 44; and metal
control part cover 48 formed of aluminum alloy and fixed onto
control part case 44 to enclose control board 46.
[0036] Control board 46 is provided with an inverter circuit which
can supply a controlled electric current to wire 18A wound around
stator section 18 of electric motor part 10A. Connector terminal 50
is disposed between control part case 44 and control part cover 48
to supply a controlled signal or electric power to an electric
element mounted on the control board 46.
[0037] Control part cover 48 is adapted to function as a heat sink
for dissipating heat generated from the electric element of control
board 46 to the outside, and therefore formed of metal. Since
control board 46 is thus provided with the inverter circuit, a
large amount of heat is generated from a switching element
comprised of MOSFET that constitutes the inverter circuit. In order
to dissipate the heat, control part cover 48 formed of metal is
used.
[0038] In electric oil pump 10 having an arrangement as mentioned
above, the start and the end of wire 18A wound around stator
section 18 constituting electric motor part 10A are connected with
an input terminal (not shown) and a neutral terminal (not shown)
attached to control part case 44, respectively, through a through
hole (not shown) formed in control part case 44 of drive control
part 42 fixed adjacent to electric motor part-accommodating portion
24. Accordingly, a driving signal controlled by the inverter
circuit is supplied to wire 18A to rotate rotor section 16 of
electric motor part 10A, thereby finally rotating pump rotor 12 to
produce the pumping action.
[0039] Electric oil pump 10 having such an arrangement is mounted
inside an engine compartment of an automotive vehicle as mentioned
above, so that corrosion is developed at a contact surface between
control part case 44 and control part cover 48 and a contact
surface between control part case 44 and pump housing 20 due to
rainwater or saltwater intruding into the engine compartment
thereby allowing the intrusion of rainwater or saltwater also into
a space accommodating control board 46 and into electric motor
part-accommodating portion 24 soon. Hence the electric element on
control board 46 and wire 18A in electric motor part 10A often
cause a short to be broken down.
[0040] This corrosion is considered to develop through a mechanism
as below. Now the mechanism will be explained, on the assumption
that a crevice defined between plastic control part case 44 and
aluminum alloy control part cover 48 is subjected to an intrusion
of saltwater and thus crevice corrosion is caused at the
interface.
[0041] At the interface, an anode reaction where Al dissolves
(Al.fwdarw.Al.sup.3++3.sup.e-) and a cathode reaction
(O.sub.2+2H.sub.2O+4.sup.e-.fwdarw.4OH.sup.-) are to develop. When
the anode reaction is so progressed as to increase the number of
Al.sup.3+, Cl.sup.- comes to migrate thereto from the periphery so
that the concentration of Cl.sup.- in the crevice is also
increased. Simultaneously, Al.sup.3+ causes hydrolysis to start
releasing H+(Al.sup.3++3H.sub.2O.fwdarw.Al(OH).sub.3+3H.sup.+)
thereby reducing pH. Thus corrosion of aluminum at the interface is
accelerated through these reactions.
[0042] In order to prevent control part cover 48 and pump housing
20 exposed to outside air from corrosion, an embodiment of the
present invention was presented in such a manner as to form an
oxide film having corrosion resistance and heat resistance on the
outer surfaces of control part cover 48 and pump housing 20 which
are brought into contact with control part case 44.
[0043] As the oxide film having corrosion resistance and heat
resistance, an embodiment of the present invention was arranged to
form a film of aluminum oxide on the outer surfaces of control part
cover 48 and pump housing 20 (both of them are formed of aluminum
alloy) to prevent corrosion by conducting anodic oxidation
treatment thereon. By having formed a film of aluminum oxide, it
becomes possible to suppress the above-mentioned reactions.
[0044] The anodic oxidation treatment is carried out by previously
shaping control part cover 48 and pump housing 20 into their
respective final forms, masking regions not needed to form an oxide
film (a film of aluminum oxide), immersing control part cover 48
and pump housing 20 in an electrolytic cell charged with an acidic
electrolyte solution such as sulfuric acid, and then causing
electrolysis where control part cover 48 and pump housing 20 serves
as anode, thereby forming an oxide film comprised of aluminum oxide
on the surface of aluminum or aluminum alloy.
[0045] By forming a film of aluminum oxide, it becomes possible to
solve the above-mentioned problem that corrosion is developed at a
contact surface between control part case 44 and control part cover
48 and a contact surface between control part case 44 and pump
housing 20 due to rainwater or saltwater intruding into the engine
compartment thereby allowing the intrusion of rainwater or
saltwater also into a space accommodating control board 46 and into
electric motor part-accommodating portion 24 soon.
[0046] Additionally, there is another problem of the temperature of
a hydraulic oil. More specifically, pump housing 20 is accommodated
in pump-accepting recess CA filled with a hydraulic oil. As an
automotive vehicle travels, the temperature of the hydraulic oil
gets increased, so that the heat of the hydraulic oil is to be
transmitted to drive control part 42 through pump housing 20 formed
of aluminum or aluminum alloy. Consequently, there arises a fear
that drive control part 42 cannot be normally operated by the
influence of the heat.
[0047] An electric oil pump according to an embodiment of the
present invention significantly receives changes in temperature
environment since it is used in an automatic transmission of an
automotive vehicle. When the hydraulic oil has low temperatures,
the hydraulic oil exhibits high viscosity and therefore the
electric current that flows through an electric motor for driving
the pump becomes large and the amount of heat generated from the
electric motor is increased; however, since the temperature of the
hydraulic oil itself and that of a working environment itself are
low, such an amount of heat as to cause problems is not transmitted
to drive control part 42.
[0048] On the contrary, when the hydraulic oil has high
temperatures, the hydraulic oil exhibits low viscosity and
therefore the electric current that flows through an electric motor
for driving the pump becomes small and the amount of heat generated
from the electric motor is decreased; however, the intense heat of
the hydraulic oil is transmitted to drive control part 42 from all
around the surfaces of pump housing 20, thereby adversely affecting
drive control part 42.
[0049] In order to suppress the amount of heat to be transmitted
from all around the surfaces of pump housing 20 immersed in the
hydraulic oil, an embodiment of the present invention was arranged
to conduct the anodic oxidation treatment on all the surfaces of
pump housing 20 intended to be brought into contact with the
hydraulic oil. An improvement in heat resistance can be expected by
forming a film of aluminum oxide on the surfaces as discussed
above. The oxide film comprising aluminum oxide is about one-thirds
of pure aluminum in thermal conductivity and therefore sufficiently
functions as a heat shield film.
[0050] Incidentally, an oxide film comprising aluminum oxide is
formed with fine pores at its surface. These fine pores cause a
deterioration of corrosion resistance. Hence sealing treatment is
performed for sealing these fine pores. Sealing treatment is
performed in a manner to increase the volume of the oxide film by
heating the film in boiling water or steam thereby sealing the fine
pores. Though the sealing treatment is mainly carried out for
enhancing the corrosion resistance, the heat resistance is also
improved. Therefore, in the case of shielding heat generated from
the hydraulic oil as in the embodiment of the present invention, it
serves as a particularly effective treatment.
[0051] When performing the anodic oxidation treatment, control part
cover 48 and pump housing 20 are previously shaped into their
respective final forms, then regions not needed to form an oxide
film (a film of aluminum oxide) are masked, then control part cover
48 and pump housing 20 are immersed in an electrolytic cell charged
with an acidic electrolyte solution such as sulfuric acid, and then
electrolysis where control part cover 48 and pump housing 20 serves
as anode is initiated thereby forming an oxide film comprising
aluminum oxide on the surface of aluminum or aluminum alloy.
[0052] Control part cover 48 and pump housing 20 having final
shapes are immersed in an electrolytic cell to cause electrolysis
therein as mentioned above; therefore, a threaded box portion of
pump housing 20 into which fastening bolt 62A is screwed thereby
electrically connecting control part cover 48 with pump housing 20
is simultaneously insulated by the oxide film, so that it becomes
impossible to let static electricity escape through fastening bolt
62A.
[0053] In addition, a through hole of pump housing 20 into which
fastening bolt 58A is inserted thereby electrically connecting
automatic transmission casing 52 with pump housing 20 is also
simultaneously insulated by the oxide film, so that it becomes
impossible to let static electricity escape through fastening bolt
58A.
[0054] As a countermeasure, masking with rubber plug or the like is
conducted on the threaded box portion of pump housing 20 into which
fastening bolt 62A for electrically connecting control part cover
48 with pump housing 20 is screwed and a portion defining the
through hole of pump housing 20 where fastening bolt 58A for
electrically connecting automatic transmission casing 52 with pump
housing 20 is inserted, so as not to form the oxide film comprising
aluminum oxide on these portions.
[0055] The configuration of electric oil pump 10 will concretely be
explained by reference to FIGS. 3 and 4. FIG. 3 is an exploded
perspective view showing electric oil pump 10 of FIG. 2 from above
and slightly diagonally, while FIG. 4 is an enlarged
cross-sectional view showing cross sections of fixing parts among
control part cover 48, control part case 44 and pump housing
20.
[0056] Since the components of electric oil pump 10 had
specifically been discussed by reference to FIG. 2, FIG. 3 will be
referred to for explanation about a method of fixing pump cover 34,
pump housing 20, control part case 44 and control part cover
48.
[0057] As shown in FIG. 3, pump housing 20 is formed having, at its
one side, pump part-accommodating portion 22 in which pump rotor 12
having an external gear and outer rotor 14 having an internal gear
are accommodated. Pump part-accommodating portion 22 in which pump
rotor 12 and outer rotor 14 are housed is enclosed by pump cover
34, and tightly fastened with fastening bolt 60A screwed into
threaded hole 60B formed in pump housing 20.
[0058] Furthermore, pump housing 20 is formed having, at the other
side, electric motor part-accommodating portion 24, in which at
least rotor section 16 and stator section 18 are housed. In this
state control part case 44 is fastened to pump housing 20 in a
manner to enclose electric motor part-accommodating portion 24.
[0059] Control board 46 is firmly fastened to control part case 44
with fastening bolts 66A, and additionally enclosed by control part
cover 48 fixed to control part case 44. In this arrangement,
fastening bolt 64A is piercingly inserted into a fixing hole formed
in cover-fixing section 64B of control part cover 48 and screwed
into a threaded hole formed in case-fixing section 64C of control
part case 44, thereby fastening control part cover 48 and control
part case 44 to each other.
[0060] Moreover, control part cover 48 and control part case 44 are
jointly fastened to pump housing 20 with fastening bolt 62A. In
this arrangement, fastening bolt 62A is piercingly inserted into a
fixing hole formed in cover-fixing section 62B of control part
cover 48 and a through hole formed in case-piercing section 62C of
control part case 44 and screwed into threaded hole 62D formed in
pump housing 20, thereby fastening control part cover 48, control
part case 44 and pump housing 20 to each other.
[0061] Pump cover 34, pump housing 20, control part case 44 and
control part cover 48 are fastened by the above-mentioned fixing
method. Then, a method of fixing pump housing 20, control part case
44, control part cover 48 and automatic transmission casing 52
according to the embodiment of the present invention will be
discussed in detail.
[0062] An embodiment of the present invention is based on the
premise that pump housing 20 and control part cover 48 shaped into
final forms and then immersed in an electrolytic cell has
previously been subjected to anodic oxidation treatment but the
surfaces of threaded box portions into which fastening bolts for
conducting static electricity are to be screwed are masked with
rubber plug or the like so as not to form the oxide film comprising
aluminum oxide thereon. Additionally, pump part-accommodating
portion 22 and a space for housing seal member 32 are also masked
with a masking member, and therefore the oxide film comprising
aluminum oxide is not formed thereon.
[0063] As shown in FIG. 4, control part cover 48 is fixed on the
upper surface of control part case 44 formed of synthetic resin.
Control part cover 48 is formed of aluminum alloy, and therefore
the surface thereof is covered with oxide film 66 formed of
aluminum oxide produced by anodic oxidation treatment. Control part
case 44 is formed integral with threaded metal bush 68 (formed of
aluminum) into which fastening bolt 64A is to be screwed, by insert
molding. This threaded metal bush 68 is disposed corresponding to
the threaded hole of case-fixing section 64C illustrated in FIG.
3.
[0064] Fastening bolt 64A is piercingly inserted into the fixing
hole formed in cover-fixing section 64B of control part cover 48
and screwed into threaded metal bush 68, thereby tightly fastening
control part cover 48 and control part case 44 to each other. The
fixing hole of cover-fixing section 64B has an inner diameter
larger than the outer diameter of a threaded portion of fastening
bolt 64A, and the inner peripheral surface of fixing hole of
cover-fixing section 64B had been covered with a rubber plug and
therefore not covered with oxide film 66. With this, fastening bolt
64A and aluminum alloy that resides inside control part cover 48
are electrically connected with each other.
[0065] On the other hand, pump housing 20 is fixed on the bottom
surface of control part case 44 formed of synthetic resin. Pump
housing 20 is also formed of aluminum alloy, and therefore the
surface thereof is covered with oxide film 66 formed of aluminum
oxide produced by anodic oxidation treatment. Fastening bolt 62A
which can fasten control part case 44 and control part cover 48
jointly to pump housing 20 has the function of leading static
electricity charged on the outer surface of control part cover 48
to aluminum alloy that resides inside control part cover 48.
[0066] Fastening bolt 62A is piercingly inserted into the fixing
hole formed in cover-fixing section 62B of control part cover 48
and the through hole formed in case-piercing section 62C of control
part case 44 and screwed into threaded hole 62D formed in pump
housing 20. The fixing hole formed in cover-fixing section 62B of
control part cover 48 has an inner diameter larger than the outer
diameter of a threaded portion of fastening bolt 62A, and the inner
peripheral surface of the fixing hole of cover-fixing section 62B
had been covered with a rubber plug and therefore not covered with
oxide film 66. With this, fastening bolt 62A and aluminum alloy
that resides inside control part cover 48 are electrically
connected with each other.
[0067] The through hole formed in case-piercing section 62C of
control part case 44 is defined by an annularly-shaped metal bush
70 (formed of aluminum) through which fastening bolt 62A pierces,
the metal bush 70 being formed integral with control part case 44
by insert molding. Metal bush 70 has the function of receiving a
load that control part case 44 formed of synthetic resin is to
receive at the time when fastening bolt 62A is screwed thereinto,
to prevent the breakdown of control part case 44. Metal bush 70
also has an inner diameter larger than the outer diameter of the
threaded portion of fastening bolt 62A.
[0068] The threaded region of fastening bolt 62A is screwed into
the threaded region of threaded hole 62D of pump housing 20,
thereby firmly fastening control part case 44 and control part
cover 48 to each other with fastening bolt 62A between the head of
fastening bolt 62A and threaded hole 62D of pump housing 20. The
threaded region of threaded hole 62D of pump housing 20 had been
covered with a rubber plug and therefore not covered with oxide
film 66. With this, fastening bolt 62A and aluminum alloy that
resides inside pump housing 20 are electrically connected with each
other.
[0069] As indicated in FIG. 4 by a thick arrow, at least static
electricity charged on the outer surface of control part cover 48
is adapted to flow from threaded hole 62D of pump housing 20 to
aluminum alloy that resides inside pump housing 20. With this,
static electricity can ensure its conductive passage at least as
far as pump housing 20.
[0070] Then, electric oil pump thus establishing the static
electricity-conductive passage is mounted on automatic transmission
casing 52 at automobile manufacturers; at this time, the embodiment
of the present invention uses pump-fastening bolt 58A for fastening
electric oil pump 10 to automatic transmission casing 52. A
threaded region of threaded hole 58C formed in pump housing 20 had
been masked with a rubber plug and therefore not covered with oxide
film 66. Accordingly aluminum alloy that resides inside pump
housing 20 and fastening bolt 58A also serve as a static
electricity-conductive passage.
[0071] Pump-fastening bolt 58A is screwed into threaded hole 58C
and additionally screwed into screw-fixing portion 52B of automatic
transmission casing 52, thereby tightly fastening pump housing 20
to automatic transmission casing 52. Pump-fastening bolt 58A and
automatic transmission casing 52 are electrically connected with
each other as a matter of course, so that static electricity on
control part cover 48 runs through passages as indicated by a thick
arrow in FIG. 4 thereby finally escaping into automatic
transmission casing 52.
[0072] As discussed above, the present invention provides an
electric oil pump with such an arrangement as to accommodate a pump
housing in a recess formed in an automatic transmission and filled
with a hydraulic oil while forming an oxide film having corrosion
resistance and heat resistance at least on the outer surface of a
control part cover (formed of metal) and the outer surface of the
pump housing (also formed of metal).
[0073] According to the present invention, an oxide film having
corrosion resistance and heat resistance is formed at least on the
outer surface of the control part cover (formed of metal) and the
outer surface of the pump housing (also formed of metal); with
this, interfaces among the control part cover, a control part case
and the pump housing are protected from corrosion. Moreover, since
the outer surface of the pump housing to be exposed to the
hydraulic oil is covered with the oxide film having corrosion
resistance and heat resistance, the pump housing is so improved in
heat resistance as to inhibit a drive control part from receiving
the influence of the heat of the hydraulic oil.
[0074] The entire contents of Japanese Patent Application
2015-030113 filed Feb. 19, 2015 are herein incorporated by
reference. Although the invention has been described above by
reference to certain embodiments and examples of the invention, the
invention is not limited to the embodiments and examples described
above. Modifications and variations of the embodiments and examples
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
* * * * *