Title: Electric power steering apparatus
Abstract: An electric power steering apparatus includes a speed reducing mechanism for decelerating the rotation of a rotatable shaft in an electric motor and a converting mechanism for converting the output rotation of the speed reducing mechanism into the axial movement of a steering shaft extending toward the right and left sides of a vehicle. The speed reducing mechanism includes an input pulley driven by the electric motor, an output pulley arranged with the steering shaft enclosed thereby, a belt for connecting the input pulley and the output pulley to each other, and a belt tension adjuster.
Patent Number: 6,938,722 Issued on 09/06/2005 to Sasaki, et al.
| Inventors:
|
Sasaki; Hiroto (Nara, JP);
Saruwatari; Takehiro (Kashiwara, JP);
Nakamura; Kensaku (Kashiba, JP);
Miyata; Atsuya (Osaka, JP);
Nagamatsu; Kazuaki (Kashiwara, JP);
Oka; Kunihiro (Kashihara, JP);
Murataka; Hiroshi (Yamato-Koriyama, JP);
Hironaka; Akihiro (Yamato-Koriyama, JP)
|
| Assignee:
|
Gates Unitta Asia Company (Osaka, JP);
Koyo Seiko Co., Ltd. (Osaka, JP)
|
| Appl. No.:
|
352249 |
| Filed:
|
January 28, 2003 |
Foreign Application Priority Data
| Jan 29, 2002[JP] | 2002-020346 |
| Jan 29, 2002[JP] | 2002-020347 |
| Feb 18, 2002[JP] | 2002-040327 |
| Feb 21, 2002[JP] | 2002-044911 |
| Current U.S. Class: |
180/444; 180/443; 474/101 |
| Intern'l Class: |
B62D 005/04 |
| Field of Search: |
474/101,112,133,136,134
180/443,444
|
References Cited [Referenced By]
U.S. Patent Documents
| 3636787 | Jan., 1972 | Nagafuchi et al.
| |
| 3768324 | Oct., 1973 | Vanderstegen-Drake.
| |
| 4568318 | Feb., 1986 | Johnson et al.
| |
| 4631044 | Dec., 1986 | Redmon.
| |
| 4686433 | Aug., 1987 | Shimizu.
| |
| 4825972 | May., 1989 | Shimizu.
| |
| 4838101 | Jun., 1989 | Dobberpuhl et al.
| |
| 4887992 | Dec., 1989 | Dixon.
| |
| 4889519 | Dec., 1989 | Band et al.
| |
| 5122198 | Jun., 1992 | von Hagen et al.
| |
| 6004236 | Dec., 1999 | Suzuki.
| |
| 6030305 | Feb., 2000 | Hood.
| |
| 6386313 | May., 2002 | Choi.
| |
| 6691819 | Feb., 2004 | Menjak et al.
| |
| 2004/0043854 | Mar., 2004 | Fraley et al.
| |
| Foreign Patent Documents |
| 2339520 | Aug., 1977 | FR.
| |
| 62-004673 | Jan., 1987 | JP.
| |
| 7-293647 | Nov., 1995 | JP.
| |
| 2000/-046136 | Feb., 2000 | JP.
| |
| WO 01/1595/9 | Mar., 2001 | WO.
| |
Other References
Ex. J-L Geyer, French Search Report, Mar. 8, 2005.
|
Primary Examiner: Dickson; Paul N.
Assistant Examiner: Yeagley; Daniel
Attorney, Agent or Firm: Rabin & Berdo P.C.
Claims
1. An electric power steering apparatus comprising an electric motor for producing
a steering assist force, further comprising:
a speed reducing mechanism for decelerating a rotation of a rotatable shaft in
the electric motor; and
a converting mechanism for converting an output rotation of the speed reducing
mechanism into an axial movement of a steering shaft extending toward right and
left sides of a vehicle,
the speed reducing mechanism comprising
an input pulley driven by the electric motor,
an output pulley arranged with the steering shaft enclosed thereby,
a belt for connecting the input pulley and the output pulley, and
means for adjusting a tension of the belt; wherein
the means for adjusting the tension includes means for changing a center-to-center
distance between the input pulley and the output pulley; wherein
the means for changing the center-to-center distance includes a guiding mechanism
for relatively guiding the first housing for holding the input pulley and the second
housing for holding the steering shaft in a predetermined guiding direction in
which the center-to-center distance can be changed; and wherein
the predetermined guiding direction includes a direction perpendicular to a plane
including center lines of the input pulley and the output pulley.
2. The electric power steering apparatus according to claim 1, wherein
the predetermined guiding direction includes a direction perpendicular to the
center lines of the input pulley and the output pulley.
3. The electric power steering apparatus according to claim 1, wherein
the guiding mechanism includes a guiding mechanism having a screw for connecting
the opposite portions of the first housing for holding the input pulley and the
second housing for holding the steering shaft and a screw insertion hole composed
of a slot provided in one of the opposite portions and extending in the predetermined
guiding direction.
4. The electric power steering apparatus according to claim 1, wherein
the means for changing the center-to-center distance further comprises a screw
which can relatively drive the first and second housings in the predetermined guiding
direction.
5. The electric power steering apparatus according to claim 1, wherein
the means for changing the center-to-center distance further comprises an elastic
member for relatively urging the first and second housings in the predetermined
guiding direction.
6. The electric power steering apparatus according to claim 1, wherein
the means for adjusting the tension includes a tensioner having a fixed member,
a movable member, a tensioner pulley supported on the movable member so as to be
rotatable and engaging with the belt, and urging means for urging the tensioner
pulley through the movable member in the direction in which tension is applied
to the belt.
7. The electric power steering apparatus according to claim 6, wherein
a slack side of the belt is pressed toward a tension side by the tensioner pulley
so that a belt wrap contact area on the input pulley expands.
8. The electric power steering apparatus according to claim 7, wherein
a pitch circle diameter of the input pulley is within a range of 12 to 30 mm,
and
a center angle of the input pulley, corresponding to the belt wrap contact area
on the input pulley, is within a range of 135 to 210 degrees.
9. The electric power steering apparatus according to claim 1, wherein
the belt comprises a cocked belt, and
the input pulley and the output pulley respectively comprise a toothed pulley.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The present invention corresponds to and claims benefit of applications No. 2002-020347
and No. 2002-020346 filed with the Japan Patent Office on Jan. 29, 2002, an application
No. 2002-040327 filed with the Japan Patent Office on Feb. 18, 2002, and an application
No. 2002-044911 filed with the Japan Patent Office on Feb. 21, 2002, all the disclosures
of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic power steering apparatus that
generates a steering assist force by an electric motor.
2. Description of Related Arts
In a rack assist type electronic power steering apparatus, the rotation of an
electric motor is decelerated through a pulley/belt mechanism, and is then converted
into the axial movement of a rack shaft through a screw ball mechanism enclosing
a rack shaft (see JP-B-4-28583, for example).
In this case, a belt is interposed in a power transmission path between the electric
motor and the rack shaft. Accordingly, a shock load and vibration from the rack
shaft are not transmitted to the electric motor.
However, vibration may be generated in the belt due to fluctuations in the
tension of the belt, and transmitted to a housing to propagate into a vehicle chamber,
to be noise.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an electric power steering apparatus
capable of reducing vibration and noise.
The present invention relates to an electric power steering apparatus comprising
an electric motor for producing a steering assist force. The apparatus further
comprises a speed reducing mechanism for decelerating the rotation of a rotatable
shaft in the electric motor; and a converting mechanism for converting the output
rotation of the speed reducing mechanism into the axial movement of a steering
shaft extending toward the right and left sides of a vehicle. The speed reducing
mechanism comprises an input pulley driven by the electric motor, an output pulley
arranged with the steering shaft enclosed thereby, a belt for connecting the input
pulley and the output pulley, and a tension adjusting mechanism for adjusting the
tension of the belt.
According to the present invention, the tension of the belt is properly
adjusted, thereby making it possible to prevent inferior operation and noise generation
caused by too much slack in the belt.
The tension adjusting mechanism may include a center-to-center distance changing
mechanism for changing a center-to-center distance between the input pulley and
the output pulley. The tension adjusting mechanism may comprise a fixed member,
a movable member, a tensioner pulley supported on the movable member so as to be
rotatable and engaging with the belt, and urging means for urging the tensioner
pulley through the movable member in the direction in which tension is applied
to the belt.
It is preferable that a supporting shaft in the input pulley is elastically supported
on a housing.
It is preferable that a pair of input pulleys, a pair of output pulleys, and a
pair of belts are respectively provided, and the input pulley and the output pulley
which correspond to each other are connected to each other by a corresponding belt.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing the schematic configuration of an electric
power steering apparatus according to a first embodiment of the present invention;
FIG. 2 is a cross-sectional view of a principal part of the electric power steering
apparatus according to the first embodiment;
FIG. 3 is a cross-sectional view taken along a line III—III shown in FIG. 2;
FIG. 4 is a cross-sectional view of a principal part of an electric power steering
apparatus according to a second embodiment of the present invention;
FIG. 5 is a cross-sectional view of a principal part of an electric power steering
apparatus according to a third embodiment of the present invention;
FIG. 6 is a cross-sectional view of a principal part of an electric power steering
apparatus according to a fourth embodiment of the present invention;
FIG. 7 is a cross-sectional view of a principal part of an electric power steering
apparatus according to a fifth embodiment of the present invention;
FIG. 8 is a cross-sectional view taken along a line VIII—VIII shown in
FIG. 7;
FIG. 9 is a cross-sectional view showing a sixth embodiment of the present invention;
FIG. 10 is a cross-sectional view of a principal part of an electric power steering
apparatus according to a seventh embodiment of the present invention;
FIG. 11 is a cross-sectional view taken along a line XI—XI shown in FIG. 10;
FIG. 12 is an enlarged view of a principal part of an input pulley and a belt
in the seventh embodiment;
FIG. 13 is a cross-sectional view of a principal part of an electric power steering
apparatus according to an eighth embodiment of the present invention;
FIG. 14 is an enlarged view of a supporting structure of an input pulley and
an input shaft in the eighth embodiment;
FIG. 15 is a cross-sectional view of a principal part of an electric power steering
apparatus according to a ninth embodiment of the present invention;
FIG. 16 is an enlarged view of a principal part of an input pulley and a belt
in the ninth embodiment;
FIG. 17 is a schematic view showing a phase shift between a pair of input pulleys
in the ninth embodiment; and
FIG. 18 is a cross-sectional view of a principal part of an electric power steering
apparatus according to a tenth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Preferred embodiments of the present invention will be described while
referring to the drawings.
First Embodiment
FIG. 1 is a schematic view showing the schematic configuration of an electric
power steering apparatus according to a first embodiment of the present invention.
Referring to FIG. 1, an electric power steering apparatus (EPS)
1 comprises
a steering shaft
3 connected to a steering wheel
2 serving as a steering
member, and a rack shaft
6 serving as a steering shaft having a pinion gear
4 provided at a front end of the steering shaft
3 and a rack gear
5 engaging with the pinion gear
4 and extending toward the right
and left sides of a vehicle.
Tie rods
7 are respectively coupled to both ends of the rack shaft
6.
Each of the tie rods
7 is connected to a corresponding wheel
8 through
a corresponding knuckle arm (not shown). When the steering wheel
2 is operated
so that the steering shaft
3 is rotated, the rotation is converted into
the linear motion of the rack shaft
6 along the right and left sides of
the vehicle by the pinion gear
4 and the rack gear
5. Consequently,
the rolling steering of the wheel
8 is achieved.
The steering shaft
3 is divided into an input shaft
9 connecting
with the steering wheel
2 and an output shaft
10 connecting with
the pinion gear
4. The input and output shafts
9 and
10 are
coaxially connected to each other through a torsion bar
11.
There is provided a torque sensor
12 for detecting a steering torque
by the amount of displacement of the relative rotation between the input shaft
9 and the output shaft
10 through the torsion bar
11. The
results of the detection of the torque by the torque sensor
12 are given
to a control section
13. In the control section
13, a voltage to
be applied to an electric motor
15 for assisting steering through a driver
14 is controlled on the basis of the results of the detection of the torque,
the results of the detection of the vehicle speed, etc. The rotation of a rotatable
shaft
16 (see FIG. 2) in the electric motor
15 is decelerated through
a speed reducing mechanism
17 including a pulley/belt mechanism. The output
rotation of the speed reducing mechanism
17 is converted into the axial
movement of the rack shaft
6 through a converting mechanism
18, so
that steering is assisted. The electric power steering apparatus
1 is of
a so-called rack assist type.
Then, FIG. 2 is an enlarged view of a principal part of the electric power
steering apparatus
1, and FIG. 3 is a schematic cross-sectional view along
a line III—III shown in FIG.
2.
Referring to FIGS. 2 and 3, a motor housing
20 in the electric motor
15 is fixed to a second housing
19 through a first housing
21.
The electric motor
15 is provided side by side with the second housing
19.
The first housing
21 holds an input pulley
28, described later, in
the speed reducing mechanism
17. The second housing
19 functions
as a rack housing accommodating the rack shaft
6.
The first housing
21 has a cylindrical shape as a whole, and is provided
with mounting flanges
22 serving as a pair of opposite portions to have
an approximately Ω shape in cross section. The second housing
19 has
mounting flanges
23 serving as opposite portions which are respectively
opposed to the mounting flanges
22 in the first housing
21. Both
the mounting flanges
22 and
23 are fastened to each other by a screw
25 in a state where a spacer
24 such as a shim is interposed between
the mounting flanges
22 and
23. The screw
25 is inserted through
a screw insertion hole
22a of the mounting flange
22, for
example, and is screwed into a screw hole
23a of the mounting flange
23.
The present embodiment is characterized in that the distance between the first
housing
21 and the second housing
19 is adjusted by adjusting the
thickness of the spacer
24, thereby adjusting the distance between center
axes
28a and
29a of the input and output pulleys
28
and
29 (a center-to-center distance D), as described later, through which
the adjustment of the tension of a belt
30 is achieved. That is, a center-to-center
distance changing member serving as a tension adjusting member is constituted by
the spacer
24.
The speed reducing mechanism
17 comprises an input shaft
27 coaxially
connected to the rotatable shaft
16 in the electric motor
15 through
a coupling joint
26 using a spline
31a, for example, an input
pulley
28 having a small diameter provided so as to be integrally rotatable
in an intermediate portion in the axial direction of the input shaft
27,
an output pulley
29 having a large diameter arranged with the rack shaft
6 serving as a steering shaft enclosed thereby, and a belt
30 wrapped
between the input and output pulleys
28 and
29. The belt
30
is composed of a toothed belt (cocked belt), for example, and the input pulley
28 is constructed as a toothed pulley having teeth engaging with the toothed
belt formed at equally spaced divisions in its circumferential direction on the
outer periphery of the input shaft
27. A toothed pulley is also similarly
used as the output pulley
29.
The input shaft
27 has first and second ends
31 and
32,
and the first and second ends
31 and
32 are supported so as to be
rotatable by corresponding supporting holes
35 and
36 in the first
housing
21 through corresponding bearings
33 and
34.
The first end
31 of the input shaft
27 is connected so as to be
integrally rotatable to the rotatable shaft
16 in the electric motor
15
through the coupling joint
26.
The first housing
21 comprises a connection housing
37 connected
to the motor housing
20 so as to cover a portion where the rotatable shaft
16 projects from the motor housing
20, and a speed reducing mechanism
housing
39 for defining an accommodation chamber
38 accommodating
a principal part of the speed reducing mechanism
17 in corporation with
the connection housing
37.
The connection housing
37 has a cylindrical shape, and accommodates the
above-mentioned coupling joint
26. The connection housing
37 has
a peripheral wall
40 and an end wall
41, and the end wall
41
is provided with the above-mentioned supporting hole
35.
The speed reducing mechanism housing
39 has a peripheral wall
42
fitted in the peripheral wall
40 of the connection housing
37 in
a fluid-tight manner, and an end wall
43. The end wall
43 is provided
with the above-mentioned supporting hole
36. The input pulley
28
is accommodated in the accommodation chamber
38 defined by the connection
housing
37 and the speed reducing mechanism housing
39. The above-mentioned
mounting flanges
22 are provided in both the connection housing
37
and the speed reducing mechanism housing
39.
As the converting mechanism
18, rotational motion can be converted into
linear motion using a ball screw mechanism or a bearing screw mechanism, for example
(see JP-A-2000-46136, for example). In the present embodiment, description is made
in conformity with an example in which the ball screw mechanism is used. The converting
mechanism
18 comprises a ball nut
44 serving as a body of rotation
surrounding the rack shaft
6.
The ball nut
44 is screwed into a ball screw groove
6a formed
in a halfway portion of the rack shaft
6 through a ball screw
45,
thereby constituting the converting mechanism
18. The ball nut
44
is supported on the rack housing
19 so as to be rotatable through a bearing
46. Further, the above-mentioned output pulley
29 is fitted in an
outer periphery
47 of the ball nut
44 so as to be integrally rotatable.
Specifically, the output pulley
29 is fixed to the ball nut
44 by
holding the output pulley
29 between a step
48 formed in the outer
periphery
47 of the ball nut
44 and a fixed screw
50 screwed
into a screw
49 in the outer periphery
47.
According to the present embodiment, the distance between the center axes
28a and
29a of the input and output pulleys
28
and
29 (the center-to-center distance D) can be adjusted easily and at low
cost by adjusting the thickness of the spacer
24 serving as a center-to-center
distance changing member composed of a shim or the like. Furthermore, the tension
of the belt
30 can be adjusted easily and at low cost, and inferior operation
and noise generation related to the belt
30 can be prevented.
Second Embodiment
Then, FIG. 4 illustrates a second embodiment of the present invention. Referring
to FIG. 4, the present embodiment differs from the first embodiment shown in FIG.
3 in that the spacer
24 is abandoned, and a first housing
21 for
holding an input pulley
28 and a rack housing
19 serving as a second
housing for holding an output pulley
29 through a bearing
46 and
a rack shaft
6 are relatively slid in a lateral direction X along their
mounting flanges
22 and
23 to adjust a center-to-center distance
D between respective center axes
28a and
29a of the
input and output pulleys
28a and
29a. The lateral direction
X is a direction approximately perpendicular to a plane P including the center
axes
28a and
29a.
In order to allow the foregoing, a screw insertion hole
22b of
the
mounting flange
22 is formed into a slot along the lateral direction X,
to guide the relative slide between both the housings
19 and
21 in
the lateral direction X through the screw insertion hole
22b composed
of the slot. The second embodiment is the same as the first embodiment shown in
FIG. 3 in that a screw hole
23a screwed into a screw
25 is
formed in the mounting flange
23. The mounting flanges
22 and
23
serving as opposite portions which are brought into contact with each other, the
screw
25, and the screw insertion hole
22b composed of the
slot constitute a guiding mechanism G
1 serving as a center-to-center distance
changing mechanism.
In the second embodiment, both the housings
21 and
19 are relatively
slid in the lateral direction X, thereby making it possible to adjust the tension
of the belt
30 easily and at low cost while achieving space saving.
Third Embodiment
Then, FIG. 5 illustrates a third embodiment of the present invention. Referring
to FIG. 5, the third embodiment differs from the second embodiment shown in FIG.
4 in that both the housings
21 and
19 are relatively slid along a
lateral direction X in the second embodiment shown in FIG. 4, while a rack housing
19 and a connection housing
37A are relatively slid along a longitudinal
direction Y to adjust a center-to-center distance D, and there is provided a single
drive screw
51 for relatively sliding the rack housing
19 and the
connection housing
37A along the longitudinal direction Y in the present
embodiment. The longitudinal direction Y is a direction approximately perpendicular
to both a center axis
28a and a center axis
29a.
Specifically, there is provided a guided section
52 composed
of an outward annular flange in a peripheral wall
40 of the connection housing
37A, and there is provided an extended section
53 extending parallel
to an input shaft
27 from an end wall
41 of the connection housing
37A. Further, an end wall
54 parallel to an end wall
43 of
a speed reducing mechanism housing
39A is provided so as to extend from
a front end of the extended section
53, and a cylindrical section
55
projecting in a stepped shape is formed in the end wall
54. An end surface
of the cylindrical section
55 forms a guided section
56. A second
end
32 of the input shaft
27 is supported so as to be rotatable by
an inner peripheral surface
55a of the cylindrical section
55
through a bearing
34.
On the other hand, the speed reducing mechanism housing
39A is integrally
formed as a part of the rack housing
19, and a guiding section
57
for guiding the above-mentioned guided section
52 is formed in the rack
housing
19 and the speed reducing mechanism housing
39A. Further,
a guiding section
58 composed of a recess, for example, for guiding the
guided section
56 is formed in the end wall
43 of the speed reducing
mechanism housing
39A. The guided sections
52 and
56 and the
guiding sections
57 and
58 constitute a guiding mechanism G
2.
The drive screw
51 is inserted through a screw insertion hole
59
of a peripheral wall
42 of the speed reducing mechanism housing
39A,
and is screwed into a screw hole
60 of the extended section
53 in
the connection housing
37A. The guiding mechanism G
2 and the drive
screw
51 constitute a center-to-center distance changing mechanism A
1.
According to the present embodiment, the tension of a belt
30 can
be adjusted easily and with high precision by managing a torque for fastening the
drive screw
51, and inferior operation and noise generation related to the
belt
30 can be prevented.
Fourth Embodiment
Then, FIG. 6 illustrates a fourth embodiment of the present invention. Referring
to FIG. 6, the present embodiment differs from the embodiment shown in FIG. 5 in
that the center-to-center distance D is increased by pulling the connection housing
37A for holding an input pulley
28 and the motor housing
20
in the operation of the single drive screw
51, to increase the tension of
the belt
30 in the embodiment shown in FIG. 5, while a center-to-center
distance D is increased by pressing a connection housing
37B for supporting
a first end
31 of an input shaft
27 and a support housing
61
for supporting a second end
32 of the input shaft
27 along a longitudinal
direction Y in the operation of a pair of drive screws
51a and
51b
arranged on both sides with a belt
30 interposed therebetween, to increase
the tension of the belt
30 in the present embodiment.
The connection housing
37B has a reduced diameter portion
62 and
a large diameter portion
63 nearer to its front end than the reduced diameter
portion
62, to support the first end
31 of the input shaft
27
through a bearing
33 by the large diameter portion
63. The large
diameter portion
63 has a guided section
64 composed of a pair of
annular flanges.
The support housing
61 has the shape of a cylinder having a bottom, to
support the second end
32 of the input shaft
27 through a bearing
34. The bottom of the support housing
61 and the annular flanges
constitute a pair of guided sections
65.
On the other hand, a speed reducing mechanism housing
39B is integrally
formed in a rack housing
19, and has a pair of holding sections
66
and
67 having a groove shape in cross section for respectively holding the
connection housing
37B and the support housing
61. A pair of opposite
walls of the holding sections
66 and
67 constitutes guiding sections
68 and
69 for respectively guiding the guided sections
64
and
65. The guided sections
64 and
65 and the guiding sections
68 and
69 for guiding the guided sections
64 and
65
constitute a guiding mechanism G
3, and the guiding mechanism G
3 and
a pair of drive screws
51a and
51b constitute a center-to-center
distance adjusting mechanism A
2 serving as a tension adjusting mechanism.
The pair of drive screws
51a and
51b is screwed into
screw holes
70 respectively formed in the holding sections
66 and
67, to abut their front ends against the large diameter portion
63
in the connection housing
37B and an outer peripheral surface of the support
housing
61.
According to the present embodiment, the input shaft
27 and an input
pulley
28 can be moved with high precision parallel to a center axis
29a
of an output pulley
29 by the pair of drive screws
51a and
51b on both sides with the belt
30 interposed therebetween.
In the present embodiment, the center-to-center distance D may be adjusted by pulling
the connection housing
37B and the support housing
61 upward in FIG.
6 by the pair of drive screws
51a and
51b.
Fifth Embodiment
Then, FIGS. 7 and 8 illustrate a fifth embodiment of the present invention.
Referring to FIGS. 7 and 8, the present embodiment is characterized in the following.
That is, a fixed housing
39C serving as a speed reducing mechanism housing
integrally formed in a rack housing
19 is provided with a circular hole
71. A movable housing
72 integrally extending from a motor housing
20 in an electric motor
15 has a circular radially outer portion
73 fitted in the circular hole
71 so as to be rotatable. Further,
the movable housing
72 has an eccentric hole
74 for respectively
supporting first and second ends
31 and
32 of an input shaft
27
so as to be rotatable through bearings
33 and
34. The center
74a
of the eccentric hole
74 is eccentric from the center
73a
of the circular radially outer portion
73 in the movable housing
72
(corresponding to the center
71a of the circular hole
71).
A center-to-center distance adjusting mechanism A
3 serving as a tension
adjusting mechanism, including the circular hole
71, the movable housing
72, and the eccentric hole
74, is constructed. Further, either one
of flanges
75 and
76 against which the fixed housing
39C and
the movable housing
72 are abutted is provided with a screw hole
77,
and the other flange is provided with a screw insertion hole
78 in a circular
arc shape. A fixed screw
79 through which the screw insertion hole
78
in a circular arc shape is inserted is screwed into the screw hole
77, to
fasten the flanges
75 and
76 in both the housings
39C and
72 to each other such that the rotational position is adjustable.
According to the present embodiment, a center-to-center distance D between
a center axis
28a of an input pulley
28 and a center axis
29a of an output pulley
29 is adjusted only by rotating the
movable housing
72, together with the motor housing
20 in the electric
motor
15, to move the center axis
28a farther away from the
center axis
29a, thereby making it possible to adjust the tension
of a belt
30. The movable housing
72 and the motor housing
20
can be also separately constructed.
Sixth Embodiment
Then, FIG. 9 illustrates a sixth embodiment of the present invention. Referring
to FIG. 9, a center-to-center distance adjusting mechanism A
4 in the present
embodiment differs from the center-to-center distance adjusting mechanism A
2
in the embodiment shown in FIG. 6 in that a pair of drive screws
51a
and
51b is replaced with the pair of elastic members
80
and
81 composed of a compression coil spring, for example.
In the sixth embodiment, a connection housing
37B and a support housing
61 for respectively supporting first and second ends
31 and
32
of an input shaft
27 are elastically urged along a longitudinal direction
Y by the elastic members
80 and
81, thereby making it possible to
automatically adjust the tension of a belt
30 to a proper value for a long time.
The present invention is not limited to each of the above-mentioned embodiments.
For example, in each of the embodiments, the input and output pulleys
28
and
29 may be formed of synthetic resin such as polyacetal resin to reduce
shock (an excitation force) caused by engagement with the belt
30, thereby
further reducing noise.
Seventh Embodiment
FIGS. 10,
11, and
12 illustrate a seventh embodiment of the present invention.
Although in FIG. 10, an electric power steering apparatus according to the
seventh embodiment is approximately the same in configuration as the electric power
steering apparatus shown in FIG. 2, it differs therefrom in that the spacer
24
is abandoned. In FIG. 10, the same components as those in the embodiment shown
in FIG. 2 are assigned the same reference numerals and hence, the description thereof
is not repeated.
Referring to FIG. 11, a tensioner T for adjusting the tension of a belt
30 is provided. The tensioner T comprises a tensioner pulley
82 for
pressing a slack side L of the belt
30 toward a tension side H. The tensioner
pulley
82 is supported on one end of a swing arm
83 serving as a
movable member so as to be rotatable through a supporting shaft
84. The
other end of the swing arm
83 is supported on a supporting bracket
85
serving as a fixed member fixed to a speed reducing mechanism housing
39
through a supporting shaft
86.
The swing arm
83 is rotated and urged in the direction in which tension
can be applied to the belt
30 (in a counterclockwise direction in FIG. 11)
by an urging member
87 composed of a torsion coil spring, for example. The
urging member
87 can use a torsion spring wrapped around the supporting
shaft
86, for example, as schematically illustrated in FIG. 11. A belt wrap
contact area R on an input pulley
28 having a small diameter is widened
by the function of the tensioner T.
The belt
30 is composed of a toothed belt (cocked belt), for example,
as shown in FIG. 12, and the input pulley
28 is constructed as a toothed
pulley having teeth
88 engaging with the toothed belt formed at equally
spaced divisions in its circumferential direction on the outer periphery of an
input shaft
27. A toothed pulley is also similarly used as an output pulley
29 having a large diameter. In FIG. 12, PCD indicates the pitch circle diameter
of the input pulley
28 having a small diameter.
According to the seventh embodiment, the belt wrap contact area R on the
input pulley
28 having a small diameter expands by pressing the slack side
L of the belt
30 toward the tension side H by the tensioner pulley
82.
Even when a pulley
28 of a small size is used as the input pulley
28
so as to ensure a high reduction gear ratio, therefore, stable torque transmission
can be achieved, and durability can be improved. By achieving the high reduction
gear ratio, it is possible to employ an electric motor having a high speed and
a low torque and also contribute to cost reduction.
Particularly when a toothed pulley engaging with the belt
30
composed of the cocked belt is used as the input pulley
28 having a small
diameter, as in the present embodiment, the number of teeth
88 engaging
with the belt
30 can be increased in the input pulley
28 having a
small diameter, thereby making it possible to increase the effect of improving durability.
When the pitch circle diameter PCD of the input pulley
28 (see FIG. 12)
is within a range of 12 to 30 mm, it is preferable that a center angle corresponding
to the belt wrap contact area R on the input pulley
28 is within a range
of 135 to 210 degrees. Consequently, it is possible to ensure a sufficient amount
of belt wrapping on the input pulley
28 having a small diameter and therefore,
to ensure stable torque transmission and durability while achieving a small size
and a high reduction gear ratio.
Eighth Embodiment
FIG.
13 and FIG. 14 which is an enlarged view illustrate an eighth embodiment
of the present invention. Referring to FIG. 13, a holding housing
39D serving
as a speed reducing mechanism housing is integrally formed in a predetermined portion
of a rack housing
19.
First and second ends
31 and
32 of an input shaft
27 are
respectively supported so as to be rotatable on corresponding supporting holes
35 and
36 of a connection housing
37 and the holding housing
39D through corresponding bearings
33 and
34.
Referring to FIG. 14, a peripheral groove
89 is formed in each of
the supporting holes
35 and
36, and a cushioning material
90A
serving as elastic supporting means is accommodated in each of the peripheral grooves
89. The cushioning materials
90A are respectively interposed between
the corresponding supporting holes
35 and
36 and outer rings
91
of the corresponding bearings
33 and
34, to elastically support the
corresponding outer rings
91. The supporting hole
35 or
36
and the outer ring
91 are loosely fitted to each other.
Furthermore, peripheral grooves
93 are respectively formed in
an outer periphery
27a of the input shaft
27 corresponding
to inner rings
92 of the bearings
33 and
34, and a cushioning
material
90B serving as elastic supporting means is accommodated in each
of the peripheral grooves
93. The cushioning materials
90B respectively
elastically support the corresponding ends
31 and
32 of the input
shaft
27. As a result, the input shaft
27 is elastically supported
on the holding housing
39D and the connection housing
37 through
the cushioning materials
90A and
90B. The input shaft
27 and
the inner ring
92 are loosely fitted to each other.
An elastic member such as synthetic rubber or synthetic resin can be used as
the
cushioning materials
90A and
90B. If an O-ring is used as an annular
elastic member, for example, however, standard components can be also employed,
resulting in reduced cost.
According to the eighth embodiment, vibrations respectively transmitted
to the holding housing
39D and the connection housing
37 from the
input shaft
27 can be significantly restrained by the functions of the cushioning
materials
90A and
90B, thereby making it possible to significantly
reduce noise within a vehicle chamber.
Although in the eighth embodiment, both the cushioning material
90A
directly receiving the outer ring
91 and the cushioning material
90B
directly receiving the input shaft
27 are provided, the present invention
is not limited to the same. For example, either one of the cushioning material
90A and the cushioning material
90B may be provided.
Furthermore, a cocked belt may not be employed as a belt.
Ninth Embodiment
FIG. 15 is an enlarged view of a principal part of an electric power steering
apparatus
1. Referring to FIG. 15, the ninth embodiment is the same as the
embodiment shown in FIG. 13 in that a motor housing
20 in an electric motor
15 is fixed to a holding housing
39D in a rack housing
19
through a connection housing
37.
In the ninth embodiment, a speed reducing mechanism
17 comprises an input
shaft
27 coaxially connected to a rotatable shaft
16 in the electric
motor
15 so as to be integrally rotatable through a coupling joint
26
using a spline
31a, for example, a pair of input pulleys
28A
and
28B provided in the input shaft
27 so as to be integrally rotatable,
a pair of output pulleys
29A and
29B having a large diameter arranged
with a rack shaft
6 serving as a steering shaft enclosed thereby, and a
pair of endless belts
30A and
30B respectively wrapped between the
input pulleys
28A and
28B and the output pulleys
29A and
29B
which respectively correspond to each other.
The belt
30A is composed of a toothed belt (a cocked belt), for example,
as shown in FIG. 16, and the corresponding input pulley
28A is constructed
as a toothed pulley having teeth
88 engaging with the toothed belt formed
at equally spaced divisions in its circumferential direction on its outer periphery.
The belt
30B is also composed of a toothed belt, and the corresponding input
pulley
28B is also constructed as a toothed pulley. Further, a toothed pulley
is also similarly used as the output pulleys
29A and
29B, which is
not illustrated. The PCD indicates the pitch circle diameter of each of the input
pulleys
28A and
28B.
Referring to FIG. 17 which is a schematic view, the respective rotational
phases of the pair of input pulleys
28A and
28B are shifted from
each other so that the teeth
88 of one of the input pulleys
28A and
28B are put at positions corresponding to tooth grooves
94 of the
other pulley.
According to the present embodiment, a torque is transmitted using the
pair of belts
30A and
30B in parallel in a torque transmission path,
thereby making it possible to reduce a torque applied to each of the belts
30A
and
30B by half, as compared with that in a conventional case where it is
transmitted by a single belt. As a result, belt vibration and noise caused thereby
can be significantly reduced. Particularly, fluctuations in the tension of the
belt in a case where a steering wheel is cut are reduced, thereby making it possible
to reduce a warming sound of the belt.
Moreover, the respective phases of the pair of input pulleys
28A
and
28B composed of the toothed pulley are shifted from each other such
that the teeth
88 of one of the input pulleys
28A and
28B
correspond to the positions of the tooth grooves
94 of the other input pulley.
Accordingly, the crest of vibration of one of the belts
30A (
30B)
is overlapped with the trough of vibration of the other belt
30B (
30A)
to cancel both the vibrations. Therefore, fluctuations in the torque can be further
reduced, to further reduce vibration and noise as a whole. Further, the fluctuations
in the tension in the case where the steering wheel is cut can be canceled, thereby
making it possible to significantly reduce the warming sound.
Tenth Embodiment
Then, FIG. 18 illustrates a tenth embodiment of the present invention. Referring
to FIG. 18, the present embodiment is characterized in that a pair of first one
way clutches
95A and
95B is interposed between an input shaft
27
and input pulleys
28A and
28B, respectively, and a pair of second
one way clutches
96A and
96B is interposed between output pulleys
29A and
29B and a ball nut
44 serving as an input section
of a converting mechanism
18, respectively. As the one way clutches
95A,
95B,
96A, and
96B, various types of known one way clutches
can be used in addition to a sprag type one way clutch, for example.
The first and second one way clutches
95A and
96A corresponding
to the one belt
30A and first and second one way clutches
95B and
96B corresponding to the other belt
30B are respectively allowed
to rotate in opposite directions.
According to the present embodiment, in cutting a steering wheel
2,
when a rotatable shaft
16 in an electric motor
15 starts to rotate
in the opposite direction, the one belt
30A which has so far rotated in
the direction of rotation of the rotatable shaft
16 starts to idle by the
corresponding first and second one way clutches
95A and
96A, and
the other belt
30B which has so far idled starts to rotate in the direction
of rotation of the rotatable shaft
16 through the corresponding first and
second one way clutches
95B and
96B, for example, to transmit a torque.
As a result, a warming sound at the time of cutting the steering wheel
2
can be solved. Further, the belt which has so far idled functions immediately when
the steering wheel
2 is cut. Accordingly, there is no time lag in belt transmission
at the time of cutting the steering wheel
2, thereby making it possible
to improve responsibility.
In the tenth embodiment, a cocked belt may not be employed as the belt.
The present invention is not limited to each of the above-mentioned embodiments.
For example, a bearing screw mechanism can be used in place of the ball screw mechanism.
Further, the rotatable shaft
16 in the electric motor
15 and the
input shaft
27 can be integrally formed.
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.
*
