U.S. patent application number 11/806620 was filed with the patent office on 2007-10-11 for electric power steering assembly and method for fabricating same.
This patent application is currently assigned to Koyo Seiko Co., Ltd.. Invention is credited to Yoshikazu Kuroumaru, Ken Matsubara, Katsutoshi Nishizaki.
Application Number | 20070235248 11/806620 |
Document ID | / |
Family ID | 34463895 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070235248 |
Kind Code |
A1 |
Matsubara; Ken ; et
al. |
October 11, 2007 |
Electric power steering assembly and method for fabricating
same
Abstract
An electric power steering assembly includes an electric motor,
a reduction mechanism for reducing the speed of an output rotation
of the electric motor, and a reduction-mechanism housing
accommodating therein the reduction mechanism. The electric motor
includes: an output shaft rotatably supported by the
reduction-mechanism housing, a motor housing formed integrally with
the reduction-mechanism housing, a rotor, and a stator assembly
accommodated in an annular space defined between the rotor and the
motor housing. When the stator assembly is assembled in the annular
space via an opening at an end portion of the motor housing, a
guided portion on an outside circumference of a stator yoke is
guided by a guide portion on an inside circumference of the motor
housing.
Inventors: |
Matsubara; Ken; (Osaka,
JP) ; Kuroumaru; Yoshikazu; (Osaka, JP) ;
Nishizaki; Katsutoshi; (Mie, JP) |
Correspondence
Address: |
RABIN & Berdo, PC
1101 14TH STREET, NW
SUITE 500
WASHINGTON
DC
20005
US
|
Assignee: |
Koyo Seiko Co., Ltd.
Osaka
JP
|
Family ID: |
34463895 |
Appl. No.: |
11/806620 |
Filed: |
June 1, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10998052 |
Nov 29, 2004 |
7235905 |
|
|
11806620 |
Jun 1, 2007 |
|
|
|
Current U.S.
Class: |
180/444 ; 29/596;
310/216.004; 310/68B; 310/75R; 310/83 |
Current CPC
Class: |
B62D 5/0412 20130101;
B62D 5/0403 20130101; Y10T 29/49009 20150115 |
Class at
Publication: |
180/444 ;
310/083; 310/068.00B; 029/596; 310/075.00R; 310/217 |
International
Class: |
H02K 15/02 20060101
H02K015/02; H02K 11/00 20060101 H02K011/00; H02K 7/10 20060101
H02K007/10; B62D 5/04 20060101 B62D005/04; H02K 15/00 20060101
H02K015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2003 |
JP |
2003-400139 |
Claims
1. A method of fabricating an electric power steering assembly
which comprises: an electric motor providing steering assist; a
reduction mechanism for speed reduction of an output rotation of
the electric motor; and a reduction-mechanism housing accommodating
therein the reduction mechanism, the electric motor including: an
output shaft rotatably supported by the reduction-mechanism
housing; a rotor having an outer periphery and being rotatable
integrally with the output shaft; a cylindrical motor housing
having an inside circumference surrounding the outer periphery of
the rotor; an annular space defined between the outer periphery of
the rotor and the inside circumference of the motor housing; and an
annular stator assembly accommodated in the annular space, the
motor housing being formed integrally with the reduction-mechanism
housing; the motor housing including an end portion disposed on an
opposite side from the reduction-mechanism housing, the end portion
of the motor housing defining an opening having a size to allow the
stator assembly to be assembled in the motor housing, the electric
motor including a cover for closing the opening at the end portion
of the motor housing, the stator assembly including a cylindrical
stator yoke having an inside circumference and an outside
circumference, and being fixed in the motor housing, the inside
circumference of the motor housing including a guide portion, the
outside circumference of the stator yoke including a guided
portion, the method comprising: a first step of assembling a
sub-assembly and the stator assembly, respectively, the
sub-assembly including the reduction-mechanism housing, the output
shaft, the rotor and the motor housing; and a second step of
assembling the sub-assembly and the stator assembly to each other;
the second step wherein the stator assembly is assembled in the
annular space via the opening at the end portion of the motor
housing in a manner that the guided portion of the stator yoke is
guided by the guide portion of the motor housing thereby preventing
the stator assembly from contacting the rotor.
Description
[0001] This is a divisional application of application Ser. No.
10/998,052, filed Nov. 29, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an electric power steering
assembly and a fabrication method thereof.
[0004] 2. Description of Related Art
[0005] An electric power steering assembly is generally designed to
transmit an output rotation of an electric motor to a steering
mechanism via a reduction mechanism including a driving gear and a
driven gear accommodated in a gear housing. The electric motor is
normally constructed independently from the reduction mechanism.
Hence, an output shaft is previously assembled to the electric
motor (motor assembly) and then, the output shaft thus assembled is
coupled with the driving gear of the reduction mechanism via a
joint. More recently, however, a new design directed to the size
reduction of the assembly has been proposed, wherein the joint is
eliminated while the output shaft of the electric motor is
integrally formed with the above driving gear (see, for example,
Japanese Unexamined Patent Publication No. 2003-113909 laid open on
Apr. 18, 2003 by Japan Patent Office)
[0006] In this case, the assembly is assembled as follows. The
output shaft is first supported by the gear housing via a bearing
and then, is assembled with a rotor. The rotor is inserted in an
inside circumference of a stator previously fixed on a motor
housing. In this state, the motor housing is fixed to the gear
housing.
[0007] According to the above publication, however, the following
problems are encountered when the rotor is assembled in the stator.
Due to the magnetic force of magnets of the rotor, the rotor is
attracted toward the stator so that the rotor is not smoothly
inserted in the inside circumference of the stator. This makes the
assembly work cumbersome. Furthermore, there is a potential fear of
the rotor brought into violent contact with the magnets as
attracted by the stator. As a result, the rotor may be damaged.
[0008] It may be contemplated to employ jigs to retain the rotor
and the stator thereby preventing the rotor from being attracted
toward the stator. However, this approach requires additional labor
for removing the mounted jigs.
[0009] In view of the foregoing, it is an object of the invention
to provide an electric power steering assembly designed to reduce
the labor involved in the assembly work and to prevent the damage
on the electric motor, as well as to provide a fabrication method
thereof.
SUMMARY OF THE INVENTION
[0010] According to an embodiment of the invention for achieving
the above object, an electric power steering assembly comprises an
electric motor providing steering assist, a reduction mechanism for
speed reduction of an output rotation of the electric motor, and a
reduction-mechanism housing accommodating therein the reduction
mechanism. The electric motor includes an output shaft rotatably
supported by the reduction-mechanism housing, a rotor having an
outer periphery and rotatable integrally with the output shaft, a
cylindrical motor housing having an inside circumference
surrounding the outer periphery of the rotor, an annular space
defined between the outer periphery of the rotor and the inside
circumference of the motor housing, and an annular stator assembly
accommodated in the annular space. The motor housing is integrally
formed with the reduction-mechanism housing. The motor housing
includes an end portion arranged on an opposite side from the
reduction-mechanism housing, whereas the end portion of the motor
housing defines an opening having a size to allow the stator
assembly to be assembled in the motor housing. The electric motor
includes a cover for closing the opening at the end portion of the
motor housing. The stator assembly includes a cylindrical stator
yoke having an inside circumference and an outside circumference,
and fixed in the motor housing. The inside circumference of the
motor housing includes a guide portion, whereas the outside
circumference of the stator yoke includes a guided portion. When
the stator assembly is assembled in the annular space via the
opening at the end portion of the motor housing, the guided portion
of the stator yoke is guided by the guide portion of the motor
housing, so as to prevent the stator assembly from contacting the
rotor.
[0011] According to the embodiment, the motor housing may be used
as a guide jig during the assembly of the stator assembly.
Specifically, when the stator assembly is inserted in the annular
space between the motor housing and the rotor, the inside
circumference of the motor housing can retain the stator assembly
so as to restrict the stator assembly from radial movement despite
magnetic attraction by magnets of the rotor.
[0012] Accordingly, the stator assembly may be mounted in the
annular space quite easily. In addition, it is ensured that both
the stator assembly and the rotor are positively prevented from
contacting each other and causing damage on each other. Since the
motor housing per se is used as the guide jig for the stator
assembly, the removal of the jig following the assembly of the
stator assembly is omitted, although the conventional art requires
the removal of the jig. Thus, the labor involved in the assembly
work may be reduced even further.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic sectional view showing a general
construction of an electric power steering assembly according to
one embodiment of the invention.
[0014] FIG. 2 is a disassembled perspective view showing a motor
housing, a stator yoke and a cover.
[0015] FIG. 3 is a diagram for explaining a method of fabricating
the electric power steering assembly.
[0016] FIG. 4 is a diagram for explaining the method of fabricating
the electric power steering assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] A preferred embodiment of the invention is described with
reference to the accompanying drawings.
[0018] FIG. 1 is a schematic sectional view showing a general
construction of an electric power steering assembly according to
one embodiment of the invention. Referring to FIG. 1, an electric
power steering assembly 1 includes a first steering shaft 3
integrally rotatably coupled to a steering member 2 such as a
steering wheel, and a second steering shaft 5 coaxially coupled to
the first steering shaft 3 via a torsion bar 4 as allowed to rotate
relative to the first steering shaft.
[0019] The second steering shaft 5 is coupled with a steering
mechanism (not shown) including a pinion, a rack shaft and the like
via a universal joint 6, an intermediate shaft (not shown) and the
like.
[0020] Thus, a torque produced by manipulating the steering member
2 is transmitted to a steering mechanism 70 such as a rack and
pinion type steering mechanism via the first steering shaft 3, the
torsion bar 4, the second steering shaft 5, the universal joint 6
and the like, whereby road wheels (not shown) can be steered.
[0021] A torque sensor 7 is provided for sensing a quantity of
relative rotational displacement between the first steering shaft 3
and the second steering shaft 5 which are interconnected via the
torsion bar 4. The torque sensor 7 supplies a detection signal to a
control unit 8 including a microprocessor and the like. Based on
the detection signal from the torque sensor 7, the control unit 8
calculates a steering torque applied to the steering member 2.
Based on the steering torque so calculated and a vehicle-speed
detection signal from a speed sensor 9, the control unit 8 controls
voltage applied, via a driver 10, to an electric motor 11 providing
steering assist. This activates the electric motor 11, an output
rotation of which is transmitted to the second steering shaft 5 via
a reduction mechanism 12, and then to the aforesaid steering
mechanism 70 via the universal joint 6 and the like. Thus is
provided the assist for the driver steering a vehicle.
[0022] The reduction mechanism 12 includes, for example, a spur
gear mechanism as a mechanism of gear pair with parallel axes.
Specifically, the reduction mechanism 12 includes a driving gear
13, and a driven gear 14 meshed with the driving gear 13 so as to
transmit the driving force to the aforesaid steering mechanism. The
driven gear 14 is coupled with the second steering shaft 5 in a
manner to be allowed to rotate integrally therewith but inhibited
from moving axially. The driving gear 13 and the driven gear 14 are
accommodated in a reduction-mechanism housing 15. Thus is formed a
speed reducer 16 including the driving gear 13, the driven gear 14
and the reduction-mechanism housing 15. The reduction-mechanism
housing 15 is formed from, for example, an aluminum alloy and
rotatably supports the second steering shaft 5 via bearings 17,
18.
[0023] The electric motor 11 comprises a brushless motor, for
example. The electric motor 11 includes an output shaft 21
rotatably supported by the reduction-mechanism housing 15 via
bearings 19, 20 such as ball bearings, a rotor 22 having an outer
periphery 22a and integrally rotatably retained by the output shaft
21, an annular stator assembly 23 surrounding the rotor 22, a
cylindrical motor housing 25 connectable with the
reduction-mechanism housing 15 to form an integral unit, and a
cover 26.
[0024] The motor housing 25 includes an inside circumference 24
defined by a cylindrical surface retaining the stator assembly 23.
An annular space 80 is defined between the outer periphery 22a of
the rotor 22 and the inside circumference 24 of the motor housing
25. The annular space 80 accommodates the stator assembly 23
therein.
[0025] The output shaft 21 is integrally formed with the driving
gear 13 by using a single member. The output shaft 21 also serves
as a support shaft of the driving gear 13, thereby realizing a
structure excluding a joint between the output shaft 21 and the
driving gear 13. Alternatively, the output shaft 21 and the driving
gear 13 may be formed separately and the driving gear 13 may be
fixed to one end of the output shaft 21.
[0026] A part of the output shaft 21, which is formed with the
driving gear 13, is accommodated in the reduction-mechanism housing
15. The other part of the output shaft 21 extends outward of the
reduction-mechanism housing 15 through an insertion hole 27. The
output shaft 21 is assembled with the aforesaid bearings 19, 20
which sandwich the driving gear 13 therebetween. The output shaft
21 is rotatably supported by support holes 28, 29 of the
reduction-mechanism housing 15 via the respectively corresponding
bearings 19, 20.
[0027] The output shaft 21 is restricted from an axial movement
relative to the reduction-mechanism housing 15 by the bearings 19,
20 and a thread member 30 threaded into the insertion hole 27 of
the reduction-mechanism housing 15. Specifically, outer rings 31,
32 of the bearings 19, 20 are fitted in individually corresponding
support holes 28, 29 of the reduction-mechanism housing 15. On the
other hand, respective inner rings 33, 34 of the bearings 19, 20
are fitted on the output shaft 21.
[0028] The outer ring 31 of the bearing 19 abuts against a step 35
of the reduction-mechanism housing 15 so as to be restricted from a
movement in a first axial direction S1 of the output shaft 21. The
inner ring 33 of the bearing 19 abuts against the driving gear 13
so as to be restricted from a movement in a second axial direction
S2 of the output shaft 21.
[0029] The inner ring 34 of the bearing 20 abuts against the
driving gear 13 so as to be restricted from a movement in the first
axial direction S1. The outer ring 32 of the bearing 20 is urged in
the first axial direction S1 of the output shaft 21 by the thread
member 30. The thread member 30 applies a pre-load to the bearings
19, 20 and also axially positions the output shaft 21.
[0030] The rotor 22 includes a spacer 36 securely fitted on an
outside circumference of the portion of the output shaft 21 that
projects from the reduction-mechanism housing 15, and a plurality
of rotor magnets 37 fixed on an outer periphery of the spacer 36 at
equal circumferential space intervals. The spacer 36 abuts against
a positioning step 38 of the output shaft 21 so as to be axially
positioned.
[0031] The motor housing 25 is formed from, for example, an
aluminum alloy. The motor hosing has openings at the both ends
thereof and surrounds the outer periphery of the rotor 22. The
motor housing 25 has a first end portion 39 and another end portion
41. The first end portion 39 is relatively farther away from the
cover 26, whereas the second end portion 40 is relatively closer to
the cover 26.
[0032] The first end portion 39 of the motor housing 25 is securely
fitted on an outside circumference of a cylindrical projection 40
of the reduction-mechanism housing 15. The cover 26 is designed to
be connected to the other end portion 41 of the motor housing
25.
[0033] The stator assembly 23 includes a cylindrical stator yoke 42
having an inside circumference 42a and an outside circumference 42b
and adapted to be fitted in the inside circumference 24 of the
motor housing 25, a plurality of stator cores 44 retained on an
inside circumference 42a of the stator yoke 42 as forming an
annular configuration, and a coil 45 wound about each of the stator
cores 44.
[0034] The stator yoke 42 is formed from a magnetic material in a
smaller thickness than that of the motor housing 25. The stator
yoke 42 is formed from the magnetic material, thereby preventing a
magnetic field within the motor housing 25 from leaking outside.
The stator yoke 42 is designed to have an outside diameter
substantially equal to an inside diameter of the motor housing 25,
so as to be clearance-fitted in the cylindrical surface defined by
the inside circumference 24 of the motor housing 25. Thus, the
stator yoke 42 is restricted from a radial movement relative to the
motor housing 25 and the rotor 22.
[0035] The inside circumference 24 of the motor housing 25 is
formed with a guide portion 81 defined by a cylindrical surface,
whereas the outside circumference 42b of the stator yoke 42 is
formed with a guided portion 82 defined by a cylindrical surface
guided by the guide portion 81.
[0036] When the stator assembly 23 is assembled in the annular
space 80 through an opening 48 at the end portion 41 of the motor
housing 25, the guided portion 82 of the stator yoke 42 is guided
by the guide portion 81 of the motor housing 25, so that the stator
assembly 23 is prevented from contacting the rotor 22.
[0037] The stator yoke 42 is formed with an annular flange 47
projected from an outside circumference of one end 46 thereof. The
stator yoke has its flange 47 received by a circumferential edge 49
of the opening 48 at the other end portion 41 of the motor housing
25, so as to be axially positioned. The flange 47 functions as an
axial positioning element for positioning the stator yoke 42 with
respect to an axial direction of the motor housing 25.
[0038] FIG. 2 is a fragmentary disassembled perspective view
schematically showing the motor housing 25, the stator yoke 42 and
the cover 26. Referring to FIG. 2, the flange 47 of the stator yoke
42 is restricted from a rotation relative to the circumferential
edge 49 of the opening 48 of the motor housing 25 by a pin 50. The
pin 50 functions as a circumferential positioning element for
positioning the stator yoke 42 with respect to a circumferential
direction of the motor housing 25.
[0039] Specifically, the flange 47 of the stator yoke 42 is formed
with a pin insertion hole 51. A plural number of pin insertion
holes 51 (two pin insertion holes formed according to the
embodiment) are formed through the flange 47 at equal
circumferential space intervals. Furthermore, pin insertion holes
52 are formed in the circumferential edge 49 of the opening 48 of
the motor housing 25. The pin insertion holes 52 are formed at
places individually corresponding to the pin insertion holes 51.
The pins 50 are inserted through the corresponding pin insertion
holes 51 and are further press-fitted in the corresponding pin
insertion holes 52 to be fixed therein.
[0040] Returning to FIG. 1, the stator cores 44 are arranged on the
cylindrical surface of the inside circumference 43 of the stator
yoke 42 at equal circumferential space intervals. The stator cores
44 are connected with one another to form an annular configuration
as a whole. The stator cores 44 are fixed to the cylindrical
surface of the inside circumference 43 of the stator yoke 42 by
press-fit for example. The stator yoke 42 surrounds the rotor 22 in
coaxial relation therewith. The coil 45 of the stator assembly 23
is connected with a connector 66, which is led out through
connector insertion holes 64, 65 of the stator yoke 42 and the
motor housing 25 so as to be exposed outside. The cover 26 is
formed from, for example, an aluminum alloy. One side face 26a of
the cover 26 is pressed against the flange 47 of the stator yoke 42
so as to close the opening 48 at the other end portion 41 of the
motor housing 25.
[0041] The electric motor 11 further includes a resolver 53 as
rotation angle detecting members for sensing a rotation angle of
the output shaft 21. The resolver 53 supplies a detection signal to
the control unit 8.
[0042] The resolver 53 includes a resolver rotor 54 as a movable
member integrally rotatably retained on an. outside circumference
of the other end of the output shaft 21, and a resolver stator 56
as a stationary member surrounding the resolver rotor 54 as
retained on an inside circumference of a retaining portion 55
defined by a cylindrical projection projected from the one side
face 26a of the cover 26. Thus is formed a cover assembly 57
including the cover 26 and the resolver stator 56.
[0043] Referring to FIG. 1 and FIG. 2, the cover 26 is fixed to the
circumferential edge 49 of the opening 48 at the other end portion
41 of the motor housing 25 by a screw 58 as a fixing member for
fixing the cover 26. As retained by the motor housing 25, the cover
26 may be turned for adjustment of the position of the resolver
stator 56.
[0044] Specifically, the cover 26 comprises a disk having a central
axis 90 disposed coaxially with the cylindrical motor housing 25.
The cover 26 includes a plurality (say two) of screw insertion
holes 59 of an arcuate form about the aforesaid central axis
90.
[0045] The screw insertion holes 59 are arranged on a circle about
the central axis 90 of the cover 26 with equal spacing and extended
along a circumferential direction of the cover 26. The flange 47 of
the stator yoke 42 is formed with screw insertion holes 60 at
places individually corresponding to the screw insertion holes 59.
Furthermore, the circumferential edge 49 of the opening 48 of the
motor housing 25 is formed with screw holes 61 (only one of which
is shown in FIG. 2) at places individually corresponding to the
screw insertion holes 59.
[0046] The cylindrical projection defining the aforesaid retaining
portion 55 of the cover 26 is formed coaxially with the central
axis 90. That is, the resolver stator 56 is disposed coaxially with
the central axis 90.
[0047] The screws 58 (as fixing members) are inserted through the
individually corresponding screw insertion holes 59 and screw
insertion holes 60 and threaded into the individually corresponding
screw holes 61. As a result, the cover 26 together with the flange
47 of the stator yoke 42 are fixed to the circumferential edge 49
of the opening 48 at the end portion 41 of the motor housing 25 by
these screws 58.
[0048] With the screws 58 loosely threaded in the screw holes 61,
the cover 26 may be turned about the central axis 90 thereof,
thereby adjusting the position (phase) of the resolver stator 56
relative to the resolver rotor 54. The adjustable range corresponds
to a range in which the screws 58 are relatively movable in the
screw insertion holes 59.
[0049] The, foregoing description is about the general construction
of the electric power steering assembly 1. Next, description is
made on a method of fabricating the electric power steering
assembly 1. FIG. 3 and FIG. 4 are diagrams for explaining the
method of fabricating the electric power steering assembly 1.
[0050] Referring to FIG. 3 and FIG. 4, the method of fabricating
the electric power steering assembly 1 comprises: a first step of
assembling a sub-assembly 62 and the stator assembly 23,
respectively; a second step of assembling the sub-assembly 62 and
the stator assembly 23 to each other; a third step of fixing the
stator assembly 23 to the sub-assembly 62 in a manner to inhibit
the relative rotation thereof; and a fourth step of assembling the
cover assembly 57 to the motor housing 25 and adjusting the
position of the resolver stator 56.
[0051] The sub-assembly 62 includes the reduction-mechanism housing
15, the output shaft 21, the rotor 22, the motor housing 25 and the
resolver rotor 54. That is, the reduction-mechanism housing 15 in
the state of the sub-assembly 62 is unitized with the motor housing
25 while retaining the output shaft 21 via the bearings 19, 20.
Furthermore, the outer peripheries of the rotor 22 and the resolver
rotor 54, which are retained by the output shaft 21, are protected
as surrounded by the motor housing 25.
[0052] The second step is carried out as follows. Firstly, through
the opening 48 at the other end portion 41 of the motor housing 25,
an end 63 of the stator yoke 42 of the stator assembly 23 is fitted
into the cylindrical surface of the inside circumference 24 of the
motor housing 25(along the second axial direction S2).
[0053] Next, the stator yoke 42 of the stator assembly 23 is pushed
into the motor housing toward the reduction-mechanism housing 15
(along the first axial direction S1 indicated by a hollow arrow).
In this process, the guided portion 82 of the stator yoke 42 of the
stator assembly 23 is guided by the guide portion 81 on the inside
circumference 24 of the motor housing 25, as allowed to move
axially but restricted from radial movement. Thus, the stator
assembly 23 is fitted in the annular space 80 between the motor
housing 25 and the rotor 22. The stator assembly 23 so fitted is
axially positioned by way of the flange 47 of the stator yoke 42
received by the circumferential edge 49 of the opening 48 of the
motor housing 25.
[0054] Referring to FIG. 2 and FIG. 4, the third step is carried
out as follows. The pins 50 are inserted through the individually
corresponding pin insertion holes 51 in the stator yoke 42 of the
stator assembly 23 and then, are pressed into the individually
corresponding pin insertion holes 52 of the motor housing 25.
[0055] After the stator assembly 23 is fixed in the sub-assembly
62, the fourth step is carried out as follows. The cover 26 is
abutted against the flange 47 of the stator yoke 42 of the stator
assembly 23 in a manner. to allow the resolver stator 56 to
surround the resolver rotor 54. Then, the screws 58 are inserted
through the individually corresponding screw insertion holes 59 of
the cover 26 and the individually corresponding screw insertion
holes 60 of the stator yoke 42 and then, are threaded into the
individually corresponding screw holes 61 of the motor housing 25.
In this process, the cover assembly 57 is turned for adjusting the
circumferential position (phase) of the resolver stator 56 before
the screws 58 are fully threaded in or in a state where the screw
insertion holes 59 are free to move relative to the screws 58.
[0056] According to the embodiment as described above, the motor
housing 25 as assembled into the state of the sub-assembly 62 is
adapted to cover the outer peripheries of the rotor 22 and the
resolver rotor 54, thereby protecting the rotor 22 and the resolver
rotor 54. This prevents the rotor 22 and the resolver rotor 54 from
being damaged by a foreign article which may inadvertently contact
the rotor or the resolver rotor when another component is assembled
to the sub-assembly 62 or the sub-assembly 62 is transported.
[0057] The stator assembly 23 is previously assembled independently
from the sub-assembly 62, thereby allowing the individual
components 42, 44, 45 of the stator assembly 23 to be fitted in the
cylindrical surface of the inside circumference 24 of the motor
housing 25 in one operation. This leads to a noticeable
labor-saving assembly work.
[0058] The stator cores are normally fixed to the inside
circumference of the motor housing by shrinkage fitting. Hence, the
stator cores are prone to impaired alignment precisions which
result from inconsistent thermal expansion/contraction of the motor
housing subjected to the shrinkage fitting. However, the embodiment
does not use the shrinkage fitting for fixing the stator cores 44,
thus obviating the aforesaid drawback of impaired alignment
precisions. As a result, the stator cores 44 may be assembled with
higher precisions.
[0059] The motor housing 25 may also be used as a guide jig during
the assembly of the stator assembly 23. Specifically, when the
stator assembly 23 is fitted in space between the motor housing 25
and the rotor 22, the cylindrical surface of the inside
circumference 24 of the motor housing 25 can retain the stator
assembly 23 so as to restrict the stator assembly 23 from the
radial movement despite the magnetic attraction by the rotor
magnets 37.
[0060] Consequently, the stator assembly 23 can be fitted in space
between the motor housing 25 and the rotor 22 quite easily. In
addition, it is ensured that the stator assembly 23 and the rotor
22 are positively prevented from contacting each other to cause
damage on each other. Since the motor housing 25 per se is used as
the guide jig for the stator assembly 23, the removal of the jig
following the assembly of the stator assembly 23 is omitted,
although the conventional art requires the removal of the jig.
Thus, the labor involved in the assembly work can be reduced even
further.
[0061] Furthermore, the stator assembly 23 may easily be axially
positioned relative to the motor housing 25 by way of the flange 47
(as an axial positioning element) which is provided at the stator
yoke 42 and which is received by the circumferential edge 49 of the
opening 48 of the motor housing 25. Of the stator assembly 23, the
portion to be disposed externally of the motor housing 25, or the
flange 47 of the stator yoke 42 is provided with the pins 50 (as
circumferential positioning elements). This facilitates the fixing
of the stator assembly 23 to the motor housing 25.
[0062] The cover assembly 57 including the cover 26 and the
resolver stator 56 is formed, thereby permitting one operation to
assemble the resolver stator 56 along with the cover 26 to the
opening 48 at the other end portion 41 of the motor housing 25.
Thus, the labor involved in the assembly work is reduced even
further. The method is arranged such that a step of fixing the
stator assembly 23 in the motor housing 25 is followed by a step of
fixing the cover 26. Thus, the stator assembly 23 is prevented from
being turned along with the cover assembly 57 when the cover
assembly 57 is turned. Hence, the position of the resolver stator
56 may be adjusted with high precisions.
[0063] The invention is not limited to the contents of the
foregoing embodiments. For instance, the motor housing 25 may be
integrally formed with the reduction-mechanism housing 15 in one
piece. The pins 50 may be press-fitted in the pin insertion holes
51 of the stator yoke 42, so that the stator assembly 23 may be
fixed in the motor housing 25 as restricted from the rotation and
axial movement relative to the motor housing. The number of the
pins 50 or of the screws 58 may be 1, or may be 3 or more. A screw
may be used in place of the pin 50. Alternatively, the pin 50 and
the screw 58 may be formed in one piece such that the positioning
and the fixing of the stator assembly 23 and the cover assembly 57
may be accomplished in one operation.
[0064] The driving gear and the driven gear are not limited to the
spur gear and helical gear may also be used. Alternatively, there
may be used a reduction mechanism including a worm shaft as the
driving gear and a worm wheel as the driven gear.
[0065] While the invention has been described in detail with
respect to specific embodiments thereof, it will be appreciated
that those skilled in the art, upon attaining an understanding of
the foregoing, may readily conceive of alterations to, variations
of, and equivalents to these embodiments. Accordingly, the scope of
the present invention should be assessed as that of the appended
claims and any equivalents thereto.
[0066] The present application corresponds to Japanese Patent
Application No. 2003-400139 filed with Japan Patent Office on Nov.
28, 2003, the whole disclosure of which is incorporated hereinto by
reference.
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