U.S. patent application number 09/769428 was filed with the patent office on 2001-08-23 for motor having speed reduction device.
Invention is credited to Torii, Katsuhiko, Yamamoto, Hiroaki.
Application Number | 20010015585 09/769428 |
Document ID | / |
Family ID | 26584696 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015585 |
Kind Code |
A1 |
Torii, Katsuhiko ; et
al. |
August 23, 2001 |
Motor having speed reduction device
Abstract
In a motor having a motor body and a speed reduction devise
composed of gear housing, a worm wheel, worm shaft with a worm, and
first and second bearings rotatably supporting the worm shaft on
opposite sides of the worm, the first bearing on a side of the
motor body inclines a given angle to a bending side of the worm
shaft, when the worm shaft is bent by an overload transmitted
thereto via the worm wheel. Accordingly, a locally concentrated
frictional wear of the bearing is reduced.
Inventors: |
Torii, Katsuhiko;
(Hamamatsu-city, JP) ; Yamamoto, Hiroaki;
(Kosai-city, JP) |
Correspondence
Address: |
LAW OFFICE OF DAVID G POSZ
2000 L STREET, N.W.
SUITE 200
WASHINGTON
DC
20036
US
|
Family ID: |
26584696 |
Appl. No.: |
09/769428 |
Filed: |
January 26, 2001 |
Current U.S.
Class: |
310/75R ;
310/112; 310/91 |
Current CPC
Class: |
F16D 3/12 20130101; F16D
3/02 20130101; F16D 41/10 20130101; F16H 2057/0213 20130101; F16D
41/105 20130101; Y10T 74/19842 20150115; H02K 7/081 20130101; Y10T
74/19847 20150115 |
Class at
Publication: |
310/75.00R ;
310/91; 310/112 |
International
Class: |
H02K 007/10; H02K
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2000 |
JP |
2000-24919 |
Feb 2, 2000 |
JP |
2000-25191 |
Claims
What is claimed is:
1. A motor having a speed reduction device comprising; a motor body
having a motor shaft for generating a driving force; a speed
reduction device having a gear housing, a worm shaft housed in the
gear housing, the worm shaft being provided with a worm, a worm
wheel housed in the gear housing and in mesh with the worm, and
first and second bearings provided in the housing, axial inner surf
aces of the first and second bearings being in contact with and
holding rotatably the worm shaft on opposite sides of the worm; and
a coupling device coupling an end of the motor shaft with an end of
the worm shaft on a side of the first bearing for transmitting the
driving force from the motor shaft via the worm shaft to the worm
wheel, wherein, when the worm shaft is bent by an overload
transmitted thereto via the worm wheel, the axial inner surface of
the first bearing maintains an axially widespreading face contact
with the worm shaft in at least one of a manner that, to follow the
bending of the worm shaft, the first bearing inclines a given angle
to a bending side of the worm shaft and a manner that the axial
inner surface of the first bearing is formed in a shape of
approximately following a bending shape of the worm shaft and
actually comes in contact with the worm shaft at positions more
extending axially toward the worm.
2. A motor according to claim 1, wherein the gear housing has a
bearing holding portion protruding outwardly therefrom to an extent
that the bearing holding portion readily inclines along with the
first bearing fixed thereto in order to follow the bending of the
worm shaft.
3. A motor according to claim 2, wherein the coupling portion has a
coupling bore and a tapered bore axially adjacent to the coupling
bore, a diameter of the tapered bore being larger toward an
opposite end to the coupling bore from which the motor shaft is
inserted into the coupling bore, and, further, wherein, when the
coupling portion inclines a given angle from an axis of the motor
shaft along with the bearing holding portion and the first bearing,
the motor shaft comes in contact with an inner surface of the
tapered bore.
4. A motor according to claim 2, wherein the coupling portion
comprises; a drive rotor into which the end of the motor shaft is
fitted, a driven rotor which is connected to the end of the worm
shaft and is coupled with the drive rotor, and a coupling housing
in which the drive and driven rotors are housed and which is fixed
to the gear housing and, further, wherein the bearing holding
portion is elastically deformable so as to incline more than the
coupling housing to follow the bending of the worm shaft.
5. A motor according to claim 2, wherein the coupling portion
comprises; a drive rotor having a coupling bore and a tapered bore
axially adjacent to the coupling bore, a diameter of the tapered
bore being larger toward an opposite end to the coupling bore from
which the motor shaft is inserted into the coupling bore, a driven
rotor which is connected to the end of the worm shaft and is
coupled with the drive rotor, and a coupling housing in which the
drive and driven rotors are housed and which is fixed to the gear
housing so that the inclination of the bearing holding portion for
following the bending of the worm shaft causes the coupling housing
and the drive and driven rotors to incline and the motor shaft
comes in contact with an inner surface of the tapered bore.
6. A motor according to claim 5, wherein the bearing holding
portion is formed in a cylinder shape, the first bearing being
fitted into an inner circumferential surface of the bearing holding
portion and the coupling housing being fitted into an outer
circumferential surface of the bearing holding portion.
7. A motor according to claim 6, wherein the bearing holding
portion is provided at the outer circumferential surface thereof on
a side of the gear housing with a plurality of ribs at constant
angular intervals and an axial end of the coupling housing is in
contact with the ribs.
8. A motor according to claim 1, wherein the first bearing is
provided with a first cylindrical inner circumferential portion
whose inner diameter is axially constant and a first tapered inner
circumferential portion axially adjacent to the first cylindrical
inner circumferential portion on a side of the worm, an inner
diameter of the first tapered inner circumferential portion is
larger toward an opposite side to the first cylindrical inner
circumferential portion, and, further, wherein the axial inner
surface of the first bearing actually in contact with the worm
shaft is normally the first cylindrical inner circumferential
portion and, when the worm shaft is bent, extends up to at least a
part of the first tapered inner circumferential portion.
9. A motor according to claim 8, wherein the second bearing is
provided with a second cylindrical inner circumferential portion
whose inner diameter is axially constant and a second tapered inner
circumferential portion axially adjacent to the second cylindrical
inner circumferential portion on a side of the worm, an inner
diameter of the second tapered inner circumferential portion is
larger toward an opposite side to the second cylindrical inner
circumferential portion, and, further, wherein the axial inner
surface of the second bearing actually in contact with worm shaft
is normally the second cylindrical inner circumferential portion
and, when the worm shaft is bent, extends up to at least a part of
the second tapered inner circumferential portion to maintain an
axially widespreading face contact with the worm shaft.
10. A motor according to claim 1, wherein the coupling device has a
clutch mechanism in which a rotating force of the motor shaft is
transmitted to the worm shaft and a rotation of the worm wheel is
not transmitted in reverse to the motor shaft.
11. A motor according to claim 8, wherein an inclination angle of
the first tapered inner circumferential portion is continuously or
stepwise changed toward the opposite side to the first cylindrical
inner circumferential portion.
12. A motor according to claim 9, wherein inclination angles of the
first and second tapered inner circumferential portions are
continuously or stepwise changed toward the opposite sides to the
first and second cylindrical inner circumferential portions,
respectively.
13. A motor according to claim 1, wherein the motor shaft and the
worm shaft are coupled with each other in the coupling device to
have a radial slight clearance within which the worm shaft is
allowed to incline a given angle to an axial direction of the motor
shaft.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of Japanese Patent Applications No. 2000-24919 filed on
Feb. 2, 2000, No. 2000-25191 filed on Feb. 2, 2000, No. 2000-283360
filed on Sep. 19, 2000, and No. 2000-369722 filed on Dec. 5, 2000,
the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a motor, in particular, a
motor having a worm and a worm wheel for speed reduction (speed
reduction device), which is applicable to a power window or a
sunroof.
[0004] 2. Description of Related Art
[0005] Conventionally, a motor to be used in a power window system
has a motor body and a speed reduction device. The speed reduction
device has a gear housing in which a worm shaft coupled coaxially
with a motor shaft of the motor body and a worm wheel in mesh with
a worm formed in the worm shaft are housed. Opposite ends of the
worm shaft are rotatably held by bearings fixed in the gear
housing.
[0006] When the motor shaft is driven to rotate, the worm shaft
rotates along with the rotation of the motor shaft so that worm
wheel rotates at a lower speed and with a higher torque than the
worm shaft. Accordingly, an output shaft connected to the worm
wheel rotates to transmit its rotational force to an outside load.
Such a motor is applicable not only to the power window system but
also the other various systems in which the output shaft rotates at
a low speed and with a high torque.
[0007] However, when an overload is applied to the output shaft
during the rotation of the motor, the worm shaft receives a large
bending force in a perpendicular direction thereto (in an opposite
direction to a position where the worm wheel is located).
Therefore, the bending force together with a rotating force
transmitted from the motor shaft causes the worm shaft to bend.
Accordingly, the conventional motor has a drawback that locally
concentrated frictional wear is likely to occur in the bearings
rotatably holding the worm shaft or the gear housing made of resin
is likely to deform, resulting in reducing a motor efficiency and
generating noises.
SUMMARY OF THE INVENTION
[0008] An object of the invention is to provide a motor in which
local frictional wear of bearings rotatably holding the worm shaft
and deformation of a gear housing are limited.
[0009] To achieve the above objects, a motor has a speed reduction
devise composed of gear housing, a worm wheel, a worm shaft with a
worm, and first and second bearings rotatably supporting the worm
shaft on opposite sides of the worm. With the motor mentioned
above, when the worm shaft is bent by an overload transmitted
thereto via the worm wheel, an axial inner surface of the first
bearing maintains an axially widespreading face contact with the
worm shaft in a manner that the first bearing inclines a given
angle toward a bending side of the worm shaft to follow the bending
of the worm shaft or in a manner that the axial inner surface of
the first bearing is formed in a shape of approximately following a
bending shape of the worm shaft and actually contacts the worm
shaft at positions more extending axially toward the worm.
[0010] It is preferable that the gear housing has a bearing holding
portion protruding outwardly therefrom to an extent that the
bearing holding portion readily inclines along with the first
bearing fixed thereto in order to follow the bending of the worm
shaft.
[0011] Further, preferably, the first bearing is provided with a
first cylindrical inner circumferential portion whose inner
diameter is axially constant and a first tapered inner
circumferential portion axially adjacent to the first cylindrical
inner circumferential portion on a side of the worm, an inner
diameter of the first tapered inner circumferential portion is
larger toward an opposite side to the first cylindrical inner
circumferential portion. In the motor having the first bearing
mentioned above, the axial inner surface of the first bearing
actually in contact with the worm shaft is normally the first
cylindrical inner circumferential portion and, when the worm shaft
is bent by a given amount, extends up to at least a part of the
first tapered inner circumferential portion.
[0012] It is preferable that the second bearing has also a second
cylindrical inner circumferential portion and a second tapered
inner circumferential portion whose constructions are same as those
of the first bearing. The First and second tapered inner
circumferential portion are arranged to face each other on opposite
sides of the worm. Therefore, the respective axial inner surfaces
of the first and second bearings are formed in a shape of
approximately following the bending shape of the worm shaft and
actually contact the worm shaft at positions more extending axially
toward the worm, when the worm shaft is bent.
BRIEF DESCRIPTION OF THE DRAWING
[0013] Other features and advantages of the present invention will
be appreciated, as well as methods of operation and the function of
the related parts, from a study of the following detailed
description, the appended claims, and the drawings, all of which
form a part of this application. In the drawings:
[0014] FIG. 1 is a cross sectional view showing a motor according
to a first embodiment of the present invention;
[0015] FIG. 2 is a partly enlarged cross sectional view of the
motor of FIG. 1;
[0016] FIG. 3 is exploded perspective views of a clutch according
to the first embodiment;
[0017] FIG. 4 is a plan view of a gear housing according to the
first embodiment;
[0018] FIG. 5 is a cross sectional view taken along a line V-V of
FIG. 2;
[0019] FIG. 6 is another cross sectional view taken along a line
V-V of FIG. 2;
[0020] FIG. 7 is a further cross sectional view taken along a line
V-V of FIG. 2;
[0021] FIG. 8 is a cross sectional view showing a motor according
to a second embodiment of the present invention;
[0022] FIG. 9 is a plan view of a gear housing according to the
second embodiment;
[0023] FIG. 10 is a partly enlarged cross sectional view of the
motor of FIG. 8;
[0024] FIG. 11 is exploded perspective views of a clutch according
to the second embodiment;
[0025] FIG. 12 is a cross sectional partial view of the clutch of
FIG. 11;
[0026] FIG. 13A is another cross sectional partial view of the
clutch of FIG. 11;
[0027] FIG. 13B is a further cross sectional partial view of the
clutch of FIG. 11;
[0028] FIG. 14 is a cross sectional view showing a motor according
to a third embodiment of the present invention;
[0029] FIG. 15 is a partly enlarged cross sectional view of the
motor of FIG. 14;
[0030] FIG. 16 is a cross sectional view of a first bearing
according to the third embodiment;
[0031] FIG. 17 is a partially enlarged cross sectional view of the
first bearing of FIG. 16;
[0032] FIG. 18 is a cross sectional view taken along a line
XVIII-XVIII of FIG. 16;
[0033] FIG. 19 is a cross sectional view of a second bearing
according to the third embodiment; and
[0034] FIG. 20 is a partially enlarged cross sectional view of the
second bearing of FIG. 19.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] (First embodiment)
[0036] A motor applicable to a power window system is described
with reference to FIGS. 1 to 7. A motor 1 is composed of a partly
flat-cylindrical motor body 2, a speed deduction device 3 and a
clutch C (refer to FIG. 2)
[0037] As shown in FIG. 1, the motor body 2 is composed of a yoke
housing 4 (hereinafter called a yoke), a pair of magnets 5, a motor
shaft 6, an armature 7, a commutator 8, resin brush holders 9 and a
pair of brushes 10 for power supply.
[0038] The yoke 4 is formed in such shape as a partly flat cylinder
having a bottom. The respective magnets 5 are fixed to face each
other to longitudinally opposite inner surfaces of the yoke 4 in a
cross section perpendicular to an axis thereof. The bottom of the
yoke 4 holds a base end of the motor shaft 6 rotating in an axis of
the yoke 6. As shown in FIG. 2, a front end of the motor shaft 6 is
provided with a coupling projection 6a having two flat surfaces in
parallel to each other.
[0039] The armature 7 is fixed to a middle part of the motor shaft
6 at a position corresponding to the positions of the magnets 5.
The commutator 8 is fixed to the motor shaft on an front end side
thereof with respect to the armature.
[0040] An opening end of the yoke 4 is provided with flanges 4a
each extending longitudinally and outwardly in a cross section
perpendicular to the axis thereof. Holes 4b and 4c for positioning
are formed in the respective flanges 4a.
[0041] The brush holder 9 is fitted and fixed to the opening end of
the yoke 4. The brush holder 9 has a holder body 9a whose shape
corresponds to that of the opening end of the yoke 4 so as to cover
substantially the opening end thereof and a connector 9b protruding
outwardly in a radial direction of the motor shaft 6 from one of
the flanges 4a (on a left side in FIG. 1). The brushes 10, which
are connected in circuit with the connector 9b by wires (not
shown), are arranged on the holder body 9a on an inner side of the
yoke 4. The holder body 9a is provided in a near center thereof
with a bearing 11, which rotatably holds the motor shaft 6 on a
front end side thereof.
[0042] The brushes 10 are arranged at positions corresponding to
that of the commutator 8 and contact the commutator 8. Current is
supplied to coil wires wound on the armature 7 via the connector
9b, the brushes 10 and the commutator 8 from a control device
(outside power source), which is not shown, so that the armature,
that is, the motor shaft 6 of the motor body 2 is driven to
rotate.
[0043] The speed reduction device 3 is composed of a resin gear
housing 21, first and second bearings 22a and 22b, a worm member
23, a warm wheel 24 and an output shaft 25.
[0044] An end of the gear housing 21 (on an upper side in FIG. 1
and hereinafter called an upper end thereof) is formed in a partly
flat-cylinder shape (nearly rectangular shape) corresponding to
that of the opening end of the yoke 4 and fixed to the motor body
2. As shown in FIG. 3, the gear housing 21 is provided at the upper
end thereof with a recess 21a into which the holder body 9a of the
brush holder 9 is fitted. The upper end of the gear housing 21 is
further provided at positions corresponding to those of the holes
4b and 4c for positioning with projections 21b and 21c that are
fitted into the holes 4b and 4c, respectively. The gear housing 21
is fastened to the yoke by screws (not shown) in a state that the
projections 21b and 21c are inserted into the holes 4b and 4c and
the holder body 9a is fitted into the recess 21a.
[0045] The gear housing 21 is provided with a long recess 21f
extending longitudinally in opposite directions from a bottom
center of the recess 21a. Further, the gear housing 21 is provided
with a circular shaped clutch housing recess 21g extending radially
from a bottom center of the long recess 21f, and with a worm shaft
housing recess 21h (refer to FIG. 2) extending in an axial
direction of the motor shaft 6 from a bottom center of the clutch
housing recess 21g. Furthermore, the gear housing 21 is provided a
wheel housing recess 21i that communicates with a middle portion of
the worm shaft housing recess 21h in a perpendicular direction to
an axis thereof (on a right side in FIG. 1).
[0046] A ring shaped flange fitting recess 21j is formed at an
opening portion of the clutch housing recess 21g. Engaging recesses
21k, which extend in a longitudinal direction of the clutch housing
recess 21g, are formed continuously at longitudinally opposite ends
of the clutch housing recess 21g.
[0047] Two basement seats 21m are formed on a bottom of the long
recess 21f. Each of the basement seats 21m is arranged around each
of the engaging recesses 21. That is, the basement seat 21m has a
wall continuous to a wall of the engaging recess 21k and is formed
near in a letter lateral U shape. Column shaped engaging
projections 21n are formed on each upper surface of the basement
seats 21m on transversely opposite ends thereof.
[0048] As shown in FIG. 2, a cylindrical bearing holding portion
21p, which may relatively easily bend in a perpendicular direction
of an axis thereof, is formed so as to protrude axially from a
bottom of the clutch housing recess 21g nearly until an axial
middle portion thereof. An inner diameter of the bearing holding
portion 21p is larger than a diameter of the worm shaft housing
recess 21h and an outer diameter thereof is smaller than an inner
diameter of the clutch housing recess 21g. The bearing holding
portion 21p is provided on an outer circumferential surface on a
base side thereof with 8 pieces of ribs 21q, which are arranged
with at 45.degree. constant angular intervals and connected with an
inner surface of the clutch housing recess 21g. Each size of the
ribs 21q is so decided that a bending amount of the bearing holding
portion 21p in a perpendicular direction to an axis thereof shows a
predetermined value relative to a given value of bending load
applied thereto.
[0049] The first and second bearings 22a and 22b, which are
cylindrical metal bearings, are fitted into the bearing holding
portion 21p and into a bottom sidewall of the worm shaft housing
recess 21h (lower side of FIG. 1), respectively. An inner diameter
of the first bearing 22a is smaller than that of the warm shaft
housing recess 21h.
[0050] The worm member 23, which is made of metal, is composed of a
worm shaft 28 and a driven rotor 29 formed integrally with the worm
shaft on a side of the motor body 2 (refer to FIG. 3). The worm
shaft 28 is provided on a middle part thereof with a worm 28a and
is housed in the worm housing recess 21h. Opposite ends of the worm
shaft 28 are rotatably held by the first and second bearings 22a
and 22b.
[0051] The worm wheel 24 is in mesh with the worm 28a and housed in
the wheel housing recess 21I so as to rotate in an axial center
thereof perpendicular to the worm shaft 28 (in a perpendicular
direction to the drawing of FIG. 1). The output shaft 25 is
connected to the worm wheel 24 so as to rotate coaxially with the
worm wheel 24. The output shaft 25 is linked via a regulator (not
shown) with a wind glass (not shown).
[0052] The motor shaft 6 is coupled via the clutch C with the worm
shaft 28. The clutch C, as shown in FIGS. 2 and 3, has the driven
rotor 29, a collar 31, a plurality of (3) rollers 32, a support
element 33, a stopper 34, a drive rotor 35 and a ball 36. The
collar 31 is composed of a cylindrical outer ring 31a, a flange 31b
extending radially and outwardly from an end (upper end in FIG. 2)
of the outer ring 31a and a pair of engagement portions 31c
extending radially and outwardly further from the flange portion
31b at 180.degree. angular intervals.
[0053] The outer ring 31a of the collar 31 is fitted into the
clutch housing recess 21g and the flange portion 31b thereof is
fitted into the flange fitting recess 21j. The collar 31 is
prevented from rotating since the engagement portions are fitted to
the engaging recesses 21k. Another end (lower end in FIG. 2) of the
outer ring 31a is fitted to reach a position near a front end
(upper end in FIG. 2) of the bearing holding portion 21p and not to
interfere the bending of the bearing holding portion 21p. The
driven rotor 29 is arranged inside the outer ring 31a.
[0054] As shown in FIG. 3, the driven rotor 29 has a shaft portion
29a extending coaxially from a base portion of the worm shaft 28
toward the motor body 2 (toward the motor shaft 6) and 3 pieces of
engaging projections 29b extending radially and outwardly from the
shaft portion 29a at 120.degree. constant angular intervals. Each
circumferential width of the engaging projections 29b becomes wider
in a radially outward direction. A radial outer surface of the
engaging projection 29b constitutes a control surface 41. A radial
distance between an inner circumferential surface 31d of the outer
ring 31a and the control surface 41 varies in a rotating direction.
The control surface 41 is a flat surface, the radial distance from
which to the inner circumferential surface 31d is shorter toward an
end of the driven rotor 29 in a rotating direction. As shown in
FIGS. 2 and 3, a round hole 29c is provided in an axial center of
the shaft portion 29a on a side of the motor body 2 (motor shaft
6). The driven rotor 29, as shown in FIG. 3, is provided with ribs
29d for reinforcing the engaging projections 29b. The ribs 29d are
formed to link circumferential side surfaces of the engaging
projections 29b at leading ends thereof on a side of the worm shaft
28 and adjacent circumferentially to each other.
[0055] The rollers 32, which are metal and formed in a near column
shape, are arranged between the control surface 41 and the inner
circumferential surface 31d. Each diameter of the rollers 32 is
smaller than a distance between a center 41a of the control surface
41 (middle part in a rotating direction) and the inner
circumferential surface 31d of the outer ring 31a and is larger
than a distance between an end 41b or 41c of the control surface
41(end part in a rotating direction) and the inner circumferential
surface 31d of the outer ring 31a. That is, the distance of the
roller 32 is equal to a distance between a middle 41d of a portion,
which bridges the center 41a and the end 41b or 41c of the control
surface 41, and the inner circumferential surface 31d of the outer
ring 31a.
[0056] A resin supporting element 33 holds rotatably the rollers 32
arranged substantially in parallel to each other at constant
intervals. As shown in FIGS. 2 and 3, the supporting elements 33 is
composed of a ring portion 33a, 3 inner extending portions 33b, 3
pairs of roller supports 33c and 3 connecting portions 33d.
Diameter of the ring portion 33a is larger than that of the outer
ring 31a. The 3 inner extending portions 33b are provided in a
radially inside circumference of the ring portion 33a at constant
angular intervals. Each pair of the roller supports 33c extends
axially from circumferentially inside and opposite ends of each of
the inner extending portions 33b. Each of the connecting portions
33d is formed in an arc shape to connect the roller supports 33c
adjacent to each other. Further, the each pair of the roller
supports 33c is provided at leading ends thereof with retainers 33e
facing each other in a circumferential direction. Each of the
rollers 32 is held not to move in axial and circumferential
directions of the ring portion 33a by the each pair of the roller
supports 33c, each of the inner extending portions 33b and each
pair of retainers 33e. The supporting element 33, which holds the
rollers 32, is assembled to the collar 31 in such a manner that
each of the roller supports 33c is inserted into an inside of the
outer ring 31a, while the rollers 32 are held between the control
surface 41 and the inner circumferential surface 31d, and the ring
portion 33a puts on and comes in contact with the flange 31b.
[0057] A stopper 34 is made of a metal sheet having even thickness.
The stopper 34 has a ring shaped contacting portion 34a whose
diameter is almost equal to that of the ring portion 33a of the
support element 33 and extending portions extending radially and
outwardly from the contacting portion 34a at 180.degree. angular
intervals. As shown in FIG. 2, outer and inner diameters of the
contacting portion 34a are equal to those of the outer ring 31a.
Each of the extending portions 34b is provided with fixing portions
34c to correspond to the engaging projections 21n of the gear
housing 21 so that the fixing portions are arranged at four corners
of the stopper 34. The stopper 34 is fixed to the gear housing by
fitting the engaging projections 21n into the fixing portions 34c.
The contacting portion 34a of the stopper 34 is arranged on an
upper surface (upper side in FIG. 1) of the ring portion 33a. As
the ring portion 33a of the support element 33 contacts the
contacting portion 34a, the stopper 34, together with the support
element 33, serves to restrict each axial movement of the rollers
32.
[0058] As shown in FIGS. 2 and 3, each of the extending portions
34b is provided at a near center thereof with a restricting portion
34d, which is formed by cutting and bending a part of the extending
portion 34b. Each end of the restricting portions contacts each
engagement portions 31c of the collar 31 so that an axial movement
of the collar is restricted.
[0059] The drive rotor 35, which is made of resin, has a shaft
portion 35a, a disk portion 35b whose diameter is larger than that
of the shaft portion 35a, and an extending portion 35c extending
axially from an axial center of the disk portion 35b. The drive
rotor 35 is provided with a ball housing recess 35d extending from
an end of the extending portion 35c until a middle of the disk
portion 35b. A wall of the ball housing recess 35d perpendicular to
an axis thereof is formed in a spherical shape. A ball 36 is held
in the ball housing recess 35d in a state that a part of the ball
36 exposes out of the end of the extending portion 35c.
[0060] The drive rotor 35 is provided at an axial center thereof
with a coupling bore 35e having two flat surfaces in parallel to
each other, which extends axially from a base end (upper end in
FIG. 2) of the shaft portion 35a to communicate to the ball housing
recess 35d. The drive rotor 35 is linked with the motor shaft 6
without rotating relative to the motor shaft 6 in such a manner
that the coupling projection 6a of the motor shaft 6 is coupled
with the coupling bore 35e. The extending portion 35c is almost
housed in the round hole 29c of the driven rotor 29 and the ball
36, which partly exposes out of the end of the extending portion
35c, is in contact with a bottom of the round hole 29c.
[0061] As shown in FIG. 3, the drive rotor 35 is provided on an end
side (lower side in FIG. 2) of the disk portion 35b with a
plurality (3 pieces) of fan shaped projections 42 which extend
radially and outwardly and protrude axially from the end of the
disk portion 35b at constant angular intervals (at predetermined
angular positions). As shown in FIG. 5, each of the projections 42
has a large arc shaped surface, whose diameter is slightly smaller
that that of the inner circumferential surface 31d of the outer
ring 31a and is formed along the inner circumferential surface 31d.
That is, the projections 42 of the drive rotor 35 are able to
axially pass through a center bore of the contacting portion 34a of
the stopper 34. Each of the projections 42 has a fitting groove 42a
(refer to FIG. 5) extending radially from a radial inside thereof
to a middle part thereof. The projections 42 are placed between the
respective engaging projections 29b of the driven rotor 29 and
between the respective rollers (respective roller supports 33c ) in
the outer ring 31a.
[0062] Rubber buffers 43 are fitted into and fixed to the
respective fitting grooves 42a. Each of the buffer 43 has a shock
absorb portion 43a protruding radially and inwardly from the
fitting groove 42a and extending in a circumferential direction
thereof. A circumferential width of the shock absorb portion 43a,
as shown in FIG. 5, is slightly larger than that of an inner
circumferential surface of the projection 42.
[0063] When the drive rotor 35 rotates counterclockwise (an arrow Y
direction in FIG. 5) to a certain position relative to the driven
rotor 29, a one side surface 43b of the shock absorb portion 43a
(on a counterclockwise side) comes in contact with a first buffer
surface 29e of the engaging projection 29b on a clockwise and
radially inner side thereof. When the drive rotor 35 rotates
counterclockwise further from the certain position, a side surface
42b of the projection 42 on a counterclockwise and radially inner
side thereof comes in contact with a first contacting surface 29f
of the engaging projection 29b on a clockwise and radially outer
side thereof. Since the shock absorb portion 43a is deformed in a
circumferential direction thereof, the drive rotor 35 may rotate
counterclockwise further from the certain position (refer to FIG.
6).
[0064] On the other hand, when the drive rotor 35 rotates clockwise
(an arrow Z direction in FIG. 5) to a certain position relative to
the driven rotor 29, another side surface 43c of the shock absorb
portion 43a (on a clockwise side) comes in contact with a second
buffer surface 29g of the engaging projection 29b on a
counterclockwise and radially inner side thereof. When the drive
rotor 35 rotates clockwise further from the certain position,
another side surface 42c of the projection 42 on a clockwise and
radially inner side thereof comes in contact with a second
contacting surface 29h of the engaging projection 29b on a
counterclockwise and radially outer side thereof. Since the shock
absorb portion 43a is deformed in a circumferential direction
thereof, the drive rotor 35 may rotate clockwise further from the
certain position.
[0065] As shown in FIG. 6, the roller 32 is located at a position
corresponding to the center 41a of the control surface 41 in a
state that the side surface 42b of the projection 42 contacts the
first contacting surface 29f of the engaging projection 29b and a
first pressing surface 42d of the projection 29b on a
counterclockwise and radially outer side thereof contacts the
roller support 33c.
[0066] Further, the roller 32 is located at a position
corresponding to the center 41a of the control surface 41 in a
state that the another side surface 42c of the projection 42
contacts the second contacting surface 29h of the engaging
projection 29b and a second pressing surface 42e of the projection
29b on a clockwise and radially outer side thereof contacts the
roller support 33c.
[0067] An operation of the motor 1 for the power window system
mentioned above is described below.
[0068] When the motor body 2 is driven to rotate the motor shaft 6
in a counterclockwise direction (the arrow Y direction in FIG. 5),
the drive rotor 35 (projections 42) rotates together with and in a
same direction to the motor shaft 6. Then, as shown in FIG. 6, when
the side surface 42b of the projection 42 contacts the first
contacting surface 29f of the engaging projection 29b and the first
pressing surface 42d of the projection 29b contacts the roller
support 33c, the roller 32 is at a position (neutral position)
corresponding to the center 41a of the control surface 41.
[0069] As the one side surface 43b of the shock absorb portion 43a
contacts the first buffer surface 29e of the engaging projection
29b in advance before the side surface 42b of the projection 42
contacts the first contacting surface 29f, a shock on contacting is
small.
[0070] At the neutral position, the driven rotor 29 is rotatable
relative to the collar 31 since the rollers 32 are not held between
the control surfaces 41 of the engaging projections 29b and the
inner circumferential surface 31d of the outer ring 31a.
Accordingly, as the drive rotor 35 further rotates
counterclockwise, a rotating force of the drive rotor 35 is
transmitted from the projections 42 to the driven rotor 29 so that
the driven rotor 29 rotates together with the drive rotor 35. At
this time, the rollers receive a rotating force in the same
direction (the arrow Y direction) from the first pressing surface
42d and move in the same direction.
[0071] To the contrary, when the motor shaft 6 rotates in a
clockwise direction (The arrow Z direction in FIG. 5), the rollers
32 are at the neutral position similarly as mentioned above. In
this state, the driven rotor 29 is rotatable relative to the collar
31 since the rollers 32 are not held between the control surfaces
41 of the engaging projections 29b and the inner circumferential
surface 31d of the outer ring 31a. Accordingly, a rotating force of
the drive rotor 35 is transmitted from the projections 42 to the
driven rotor 29 so that the driven rotor 29 rotates together with
the drive rotor 35.
[0072] Then, the worm shaft 28 rotates together with the driven
rotor 29 so that the worm wheel and the output shaft 25 rotates for
closing or opening the window glass linked with the output shaft
25.
[0073] On the other hand, when a load is applied to the output
shaft 25 in a state that the motor 1 stops, the load causes the
driven rotor 29 to rotate clockwise (the arrow Z direction in FIG.
5). As a result, each of the rollers 32 is moved relative to the
driven rotor 29 toward the end 41b (the middle 41d) of the control
surface 41 of the engaging projection 29b. As shown in FIG. 7, when
the roller 32 makes a relative movement up to the middle 41d, the
roller 32 is held (rocked) between the control surface 41 and the
inner circumferential surface 31d of the outer ring 31a. As the
outer ring 31a is fixed, further rotation of the driven rotor 29 is
prevented without a follow rotation of the drive rotor 35.
[0074] To the contrary, when the driven rotor 29 is rotated in a
counterclockwise (the arrow Y direction in FIG. 5), each of the
rollers 32 is moved relative to the driven rotor 29 toward the end
41c (the middle 41d) of the control surface 41 of the engaging
projection 29b, since the drive rotor stops. Then, when the roller
32 makes a relative movement up to the middle 41d, the roller 32 is
held (rocked) between the control surface 41 and the inner
circumferential surface 31d of the outer ring 31a. As the outer
ring 31a is fixed, further rotation of the driven rotor 29 is
prevented without a follow rotation of the drive rotor 35.
[0075] As mentioned above, even if large load is applied to the
output shaft 25, the rotation of the driven rotor 29 is prevented.
Accordingly, the window glass linked with the output shaft 25 is
never opened or closed by its gravity or the load from outside.
[0076] Further, as the clutch C has a slight clearance between an
outer surface of the drive rotor 35 (the large arc surfaces of the
projections) and the inner circumferential surface 31d of the outer
ring 31a, alignment gaps (radial displacement and inclination) as
to axes of the drive rotor 35, the collar 31 and the driven rotor
29 are allowed, if they fall within a given range. That is, the
clutch C serves to allow a given amount of alignment gap (radial
displacement and inclination) between the motor shaft 6 and the
worm shaft 28.
[0077] When an overload is applied to the output shaft 25 during a
driving operation of the motor 1, a middle part of the worm shaft
28 receives a large bending force in a perpendicular direction
thereto (in an arrow X direction in FIG. 1) so that the bending
force together with a rotating force transmitted from the motor
shaft 6 causes the worm shaft 28 to bend. As the bearing holding
portion 21p is formed to readily bend from a body of the gear
housing 21, the first bearing 22a and the bearing holding portion
21p are inclined by following the bending of the worm shaft 28 so
that a large frictional force, which is concentrated locally, is
not applied to an axial end of the first bearing 22a.
[0078] Further, when a rotating force is applied to the output
shaft 25 while the motor stops, the middle part of the worm shaft
28 receives a large bending force in a perpendicular direction
thereto (in an arrow X direction in FIG. 1) which causes the worm
shaft 28 to bend since a reverse rotation is prevented by the
clutch C. As the bearing holding portion 21p is formed to readily
bend from a body of the gear housing 21, the first bearing 22a and
the bearing holding portion 21p are inclined by following the
bending of the worm shaft 28 so that a large frictional force,
which is concentrated locally, is not applied to an axial end of
the first bearing 22a.
[0079] As mentioned above, in the motor according to the first
embodiment, local frictional wear of the first bearing 22a is
limited. Further, the gear housing 21 is prevented from deforming
plastically to such an extent that a relative position between the
worm shaft housing recess 21h and the wheel housing recess 21i is
changed. As a result, a motor efficiency reduction and a noise
generation are prevented.
[0080] Further, even if the worm shaft 28 and the bearing holding
portion 21p are bent and inclined within the given range mentioned
above due to the overload applied to the output shaft 25, the motor
shaft 6 is not be bent and inclined.
[0081] (Second embodiment)
[0082] A motor according to a second embodiment is described with
reference to FIGS. 8 to 13B. The motor is composed of a motor body
51, a speed reduction device 52 and a clutch 53. The motor body 51
has a cylindrical yoke 54 having a bottom, bearings 55a and 55b
that are fixed to the yoke 54, a motor shaft 56 rotatably held by
the bearings 55a and 55b, and an armature fixed to the motor shaft
56. The motor shaft 56 is provided at an end thereof (an end on an
opening end side of the yoke 4 and shown on a right side in FIG. 8)
with a coupling portion 56a whose cross section is formed in a
letter D shape.
[0083] The speed reduction device 52 is composed of a resin gear
housing 21 whose end (left side end in FIG. 8) is fastened by
screws to the yoke 54, first and second bearings 59 and 60, a worm
shaft 61, a warm wheel 62 and an output shaft 63.
[0084] The gear housing 58 is provided with a worm shaft housing
recess 64 extending in an axial direction of the motor shaft 56
from an end thereof (left side end in FIG. 8), and a wheel housing
recess 65 that communicates with a middle portion of the worm shaft
housing recess 64 in a perpendicular direction to an axis thereof
(on an upper side in FIG. 8).
[0085] As shown in FIG. 10, the gear housing 58 is further provided
at an end (opening end) of the worm shaft housing recess 64 with a
recess 66 whose inner diameter is larger than that of the worm
shaft housing recess 64.
[0086] A bearing holding portion 67, which may be bent
perpendicularly to an axis thereof, is formed to protrude out of
the gear housing 58 into the recess 66 on a bottom side. The
bearing holding portion 67, whose inner diameter is larger than
that of the worm shaft housing recess 64 and whose outer diameter
is smaller that an inner diameter of the recess 66, is formed in a
cylindrical shape to extend axially until about a middle portion of
the recess 66. An inside bottom surface 67a bridging an inner
surface of the bearing holding portion 67 and an inner surface of
the worm shaft housing recess 64 is located at a position more
protruding in the recess 66 than that an outer bottom surface
bridging an outer surface of the bearing holding portion 67 and an
inner surface of the recess 66. The bearing holding portion 67 is
provided on an outer circumferential surface on a base side thereof
(right side in FIGS. 8 and 10) with 8 pieces of ribs 68, which are
arranged with at 45.degree. constant angular intervals and
connected with the inner surface of the recess 66. Each size of the
ribs 68 is so decided that a bending amount of the bearing holding
portion 67 in a perpendicular direction to an axis thereof shows a
predetermined value relative to a given value of bending load
applied thereto.
[0087] The bearing holding portion 67 is provided on an outer
surface on a front-end side thereof with a serration 69 having a
plurality of nearly triangle teeth.
[0088] The first bearing 59, which is a cylindrical sliding
bearing, is fitted into the bearing holding portion 67 so that an
end thereof (right side end in FIGS. 8 and 10) is in contact with
the inner bottom surface 67a. An inner diameter of the first
bearing 59 is smaller than that of the worm shaft housing recess
64. The second bearing 60 is fitted into a bottom sidewall of the
worm shaft housing recess 64.
[0089] The worm shaft 61 is provided on a middle part thereof with
a worm 70 and is housed in the worm housing recess 64. Opposite
ends of the worm shaft 61 are rotatably held by the first and
second bearings 59 and 60. The worm shaft 61 is provide at an end
thereof (left side in FIG. 8) with an engaging recess whose cross
section is formed nearly in a square shape.
[0090] The worm wheel 62 is in mesh with the worm 70 and housed in
the wheel housing recess 65 so as to rotate in an axial center
thereof perpendicular to the worm shaft 61 (in a perpendicular
direction to the drawing of FIG. 8). The output shaft 63 is
connected to the worm wheel 62 so as to rotate coaxially with the
worm wheel 62.
[0091] The motor shaft 56 is coupled via the clutch 53 with the
worm shaft 61. The clutch 53, as shown in FIG. 11, has a clutch
housing 71, a drive rotor 72, a ball 73, driven rotor 74, a
plurality of (3) rollers 72, and a ring 76.
[0092] The drive rotor 72, which is made of resin, has a shaft
portion 72a and a disk portion 72b whose diameter is larger than
that of the shaft portion 72a. The drive rotor 72 is provided at a
center thereof with a spherical shaft hole 72c and a coupling bore
72d whose cross section is formed in a letter D shape and which is
adjacent to a base end (lower side in FIG. 11) of the spherical
shaft hole 72c. The coupling portion 56a of the motor shaft 56 is
coupled with the coupling bore 72d, as shown in FIG. 11, without a
relative rotation to the coupling bore 72d. The disk portion 72b is
further provided adjacent to the coupling bore 72d with a tapered
portion 72e whose diameter is larger toward an opening from which
the motor shaft 56 (coupling portion 56a) is inserted into the
coupling bore.
[0093] The disk portion 72b is provided on a front side thereof
(upper side in FIG. 11) with a plurality (3 pieces) of projections
81, which extend along an outer circumferential surface thereof and
in an axial direction thereof at constant angular intervals so that
openings 83 are formed between the projections adjacent to each
other. As shown in FIG. 12, each of the projections 81 is provided
on an inner wall surface thereof (radially inner surface) with a
protruding piece 81a protruding toward a center thereof so that a
plurality of (3) fan shaped engaging grooves 82, which are
positioned between the protruding pieces 81a adjacent to each other
and communicate with each other on center axial sides thereof, are
formed at constant angular intervals.
[0094] As shown FIG. 11, the ball 73, which is made of metal, is
housed rotatably in the spherical shaft hole 72c not to drop out
therefrom.
[0095] The driven rotor 74 has a disk portion 74a and a fitting
portion 74b whose cross section is formed in a square shape and
which protrudes from a center thereof toward a front end thereof
(upper side in FIG. 11). The fitting portion 74b, as shown in FIG.
10, is fixed to the engaging recess 61a of the worm shaft 61
without a relative rotation thereto.
[0096] As shown in FIG. 12, the disk portion 74a is provided with a
plurality of (3 pieces) of fan shaped engagement projections 84
extending radially and outwardly at constant angular intervals. The
engagement projections 84 are rotatably housed in the engaging
grooves 82. The driven rotor 74 is in a point contact with the ball
73 housed in the spherical shaft hole 72c and a rotation thereof is
smooth.
[0097] Each of the engagement projections is provided with a
control surface 84a which is formed by cutting off straight an
outer circumferential surface from opposite ends toward a center
thereof so that a diameter of the center is shorter than the end
thereof.
[0098] The drive rotor 72 housing the driven rotor 74 is housed
rotatably in a clutch housing 71 with a slight clearance between an
inner surface of the clutch housing 71 and an outer surface
thereof.
[0099] As shown in FIG. 11, the clutch housing 71 has a nearly
cylindrical outer ring 71a and a bottom portion 71b having a center
hole 71c at an axial center thereof. The shaft portion 72a of the
drive rotor 72 is inserted rotatably into the center hole 71c. The
outer ring 71a is provided at inner circumferential surface on an
opening side thereof with a serration 71d having a plurality of
nearly triangle teeth groove. As shown in FIG. 10, the serration 69
of the bearing holding portion 67 is fitted into the serration 71d
until an end of the outer ring 71a on an opening side thereof comes
in contact with the ribs 68.
[0100] As shown in FIG. 12, rollers 75 are arranged in a space
formed by an inner circumferential surface of the outer ring 71a,
respective first and second surfaces 83a and 83b of the openings 83
and the control surfaces 84a of the engagement projections 84.
[0101] Each of the rollers 75, which is a column, is arranged in
such a manner that a center axis thereof is in parallel to that of
the clutch 53. Each diameter of the rollers 75 is smaller than a
distance between a center of the control surface 84a and the inner
circumferential surface of the outer ring 71a and is larger than a
distance between an end of the control surface 84a and the inner
circumferential surface of the outer ring 71a. The ring 76 is
arranged on a front end (upper side in FIG. 11) of the driven rotor
74. The ring 76, which is made of resin, is press fitted into the
outer ring 71a of the clutch housing 71 so that axial movements of
rollers 75 are restricted.
[0102] As shown in FIG. 13A, when the drive rotor 72 rotates 81b in
a direction shown by an arrow (clockwise), a side surface 84b
(counterclockwise side) of the engagement projection 84 comes in
contact with and is pressed by a side surface 81b (clockwise side)
of the protruding piece 81a. To the contrary, when the drive rotor
72 rotates counterclockwise, another side surface 84c (clockwise
side) of the engagement projection 84 comes in contact with and is
pressed by another side surface 81c (counterclockwise side) of the
protruding piece 81a. In cases mentioned above, as each of the
rollers 75 is pushed by the opening 83 to locate at a position
corresponding to a center of the control surface 84a, a rotation of
the driven rotor 74 is not interrupted and the driven rotor 74
rotates together with the driven rotor 72.
[0103] On the other hand, as shown in FIG. 13B, when the driven
rotor 74 rotates in a direction shown by an arrow
(counterclockwise), each of the rollers 75 makes a relative
movement toward an end of the control surface 84a and held (rocked)
between the control surface 84a and the inner circumferential
surface of the outer ring 71a. To the contrary, when the driven
rotor 74 rotates, each of the rollers 75 makes a relative movement
toward another end of the control surface 84a and held (rocked)
between the control surface 84a and the inner circumferential
surface of the outer ring 71a. Since the outer ring 71a is fixed to
the speed reduction device (bearing holding portion 67), further
rotation of the driven rotor 74 is prevented without a follow
rotation of the drive rotor 72.
[0104] As the clutch 53 has a slight clearance between the outer
circumferential surface of the drive rotor and the inner
circumferential surface of the clutch housing 71, a radial relative
movement of the drive rotor 72 to the clutch housing 71 within a
given range (by a length of the clearance) is allowed. Further,
since the coupling bore 72d has the tapered portion 72e, an
inclination of the motor shaft 56 to a center axis of the coupling
bore 72d at a given angular range (by an inclination angle of the
tapered portion 72e) is allowed. That is, the clutch 53 serves to
allow a given amount of alignment gap (radial displacement and
inclination) between the motor shaft 56 and the worm shaft 61.
[0105] With the motor mentioned above, when the motor body 51 is
driven to rotate the motor shaft 56, a driving force is transmitted
via the clutch 53 to the worm shaft 61 so that the worm shaft 61
rotates. Then, the worm wheel 62 rotates at a lower rotating speed
and a higher torque than the worm wheel 61. Accordingly, the output
shaft 63 rotates to transmit the rotating force to an outside load
according to the rotation of the worm wheel 62.
[0106] When an overload is applied to the output shaft 63 during a
driving operation of the motor, a middle part of the worm shaft 61
receives a large bending force in a perpendicular direction thereto
(in an arrow X direction in FIG. 8) so that the bending force
together with a rotating force transmitted from the motor shaft 56
causes the worm shaft 61 to bend. As the bearing holding portion 67
is formed to readily bend from a body of the gear housing 58, the
first bearing 59 and the bearing holding portion 67 are inclined by
following the bending of the worm shaft 61 so that a large
frictional force, which is concentrated locally, is not applied to
an axial end of the first bearing 59.
[0107] Further, when a rotating force is applied to the output
shaft 63 while the motor stops, the middle part of the worm shaft
61 receives a large bending force in a perpendicular direction
thereto (in an arrow X direction in FIG. 8) which causes the worm
shaft 61 to bend since a reverse rotation is prevented by the
clutch 53 As the bearing holding portion 67 is formed to readily
bend from a body of the gear housing 58, the first bearing 59 and
the bearing holding portion 67 are inclined by following the
bending of the worm shaft 61 so that a large frictional force,
which is concentrated locally, is not applied to an axial end of
the first bearing 59.
[0108] As mentioned above, in the motor according to the second
embodiment, local frictional wear of the first bearing 59 is
limited. Further, the gear housing 58 is prevented from deforming
plastically to such an extent that a relative position between the
worm shaft housing recess 64 and the wheel housing recess 65 is
changed. As a result, a motor efficiency reduction and a noise
generation are prevented.
[0109] Further, even if the worm shaft 61 and the bearing holding
portion 67 are bent and inclined within the given range mentioned
above due to the overload applied to the output shaft 63, the motor
shaft 56 is not be bent and inclined due to the tapered surface
72e.
[0110] Furthermore, as the inner surface of the bearing holding
portion 67 holds the first bearing 59 and the outer surface of the
bearing holding portion 67 is in an serration engagement with the
clutch housing 71, the construction of the gear housing 58 is not
complicated and an axial length of the motor becomes shorter.
[0111] Since the clutch housing 71 is inserted into the bearing
holding portion 67 until the end thereof comes in contact with the
ribs 68, axial positioning of the clutch 53 is easy.
[0112] Moreover, instead of engaging the serration 71d of the
clutch housing 71 with the serration 69 formed at the outer
circumferential surface of the bearing holding portion 67, the
clutch housing 71 may be held by a holding portion provided
separately from the bearing holding portion 67 in the gear housing
or the outer ring 71a of the clutch housing 71 may be fitted into
the recess 66 of the gear housing.
[0113] Further, instead of forming the bearing holding portion 21p
or 67 according to the first or second embodiment in the
cylindrical shape, the bearing holding portion 21p or 67 may be
composed of a first and second holding pieces each of which has a
shape formed by cutting a cylindrical body at 90.degree. and which
are arranged to face each other.
[0114] (Third embodiment)
[0115] A motor according to a third embodiment is described with
reference to FIGS. 14 to 20. The motor according to the third
embodiment is similar to the motor according to the second
embodiment. A difference is that, instead of the first and second
bearings 59 and 60 each having a through-hole whose diameter is
axially constant, each of first and second bearings 180 and 190 of
the third embodiment has a through- hole provided with a
cylindrical portion and a tapered portion adjacent to the
cylindrical portion, as shown in FIGS. 14 and 15.
[0116] The first bearing 180 is a cylindrical oil retaining bearing
made of porous sintered metal having bores in which lubricant oil
is contained. As shown in FIGS. 16 to 18, the first bearing 180 has
an axially extending through-hole 182. An inner circumferential
surface 184 of the through-hole 182 is composed of a cylindrical
portion 186, whose diameter is axially constant, on an opposite
side of the worm 70 and a tapered portion 188, whose diameter is
larger toward an opening end on a side of the worm 70, adjacent to
the cylindrical portion 186.
[0117] The tapered portion 188 is constituted by first to third
taper portions 188A, 188B and 188C, as shown in FIG. 16. Further,
as shown in FIG. 17, taper angles .theta.1, .theta.2 and .theta.3
of the first to third taper portions 188A, 188B and 188C are larger
toward the opening end. That is, a relation of
.theta.1<.theta.2<.theta.3 is satisfied.
[0118] To connect smoothly the respective taper angles .theta. 1,
.theta.2 and .theta.3 form the cylindrical portion 186 toward the
first to third taper portions 188A, 188B and 188C, respective
boundary portions thereof are provided with round surfaces.
Further, as shown in FIG. 18, the inner circumferential surface 184
of the through-hole 182 is provided with a finely finished surface
189 formed by partly filling up the bores.
[0119] The second bearing 190, similar to the first bearing 180, is
a cylindrical oil retaining bearing made of porous sintered metal
having bores in which lubricant oil is contained. As shown in FIGS.
19 and 20, the second bearing 190 has an axially extending
through-hole 192. An inner circumferential surface 194 of the
through-hole 192 is composed of a cylindrical portion 196, whose
diameter is axially constant, on an opposite side of the worm 70
and a tapered portion 198, whose diameter is larger toward an
opening end on a side of the worm 70, adjacent to the cylindrical
portion 196.
[0120] The tapered portion 198 is constituted by fourth to sixth
taper portions 198A, 198B and 198C, as shown in FIG. 19. Further,
as shown in FIG. 20, taper angles .theta.4, .theta.5 and .theta. 6
of the fourth to sixth taper portions 198A, 198B and 198C are
larger toward the opening end. That is, a relation of
.theta.4<.theta.5<.theta.6 is satisfied.
[0121] Further, the inner circumferential surface 194 of the
through-hole 192 is provided with a finely finished surface 199,
similar to the finished surface 189, formed by partly filling up
the bores.
[0122] In the motor having the first and second bearings 10 and
190, when an overload is applied to the output shaft 63 during a
driving operation of the motor, a middle part of the worm shaft 61
receives a large bending force in a perpendicular direction thereto
(in an arrow X direction in FIG. 14) so that the bending force
together with a rotating force transmitted from the motor shaft 56
causes the worm shaft 61 to bend.
[0123] As the first and second bearing 180 and 190, which rotatably
hold the worm shaft 61, have the cylindrical portions 186 and 196
and the tapered portions 188 and 198 whose taper angles are larger
gradually toward the worm 70, axial inner surfaces of the first and
second bearing 180 and 190 actually in contact with the worm shaft
61 extends up to the tapered portions 188 and 198 to follow
approximately a bending shape of the worm shaft 61 so that axially
widespreading face contacts with the worm shaft 61 are
maintained.
[0124] At this time, the worm shaft 61 is mainly in slidable
contact with the finely finished surfaces 189 and 199 of the first
and second bearings 180 and 190, against which the worm shaft 61 is
pushed due to the bending thereof. Accordingly, local frictional
wear of the bearings 180 and 190 are limited, and a motor
efficiency reduction and a noise generation are also prevented.
[0125] Further, the bearing holding portion 67 may be designed to
incline a certain angle together with first bearing 180, as
mentioned in the second embodiment, or not to incline by adjusting
the size or the strength of the ribs 68. If the bearing holding
portion 67 inclines the certain angle, an axial length of the
tapered portion 188 of the first bearing 180 in actual contact with
the worm shaft 61 becomes shorter.
* * * * *