U.S. patent application number 10/079610 was filed with the patent office on 2002-09-05 for electric motor assist type power steering apparatus.
This patent application is currently assigned to HONDA GIKEN KOGYO KABUSHIKI KAISHA. Invention is credited to Shimizu, Yasuo, Terada, Yasuhiro, Watanabe, Katsuji.
Application Number | 20020121401 10/079610 |
Document ID | / |
Family ID | 18919711 |
Filed Date | 2002-09-05 |
United States Patent
Application |
20020121401 |
Kind Code |
A1 |
Shimizu, Yasuo ; et
al. |
September 5, 2002 |
Electric motor assist type power steering apparatus
Abstract
To provide the electric motor assist type power steering
apparatus, which can prevent the aggravation of the feeling of the
steering, and which can transmit the assist steering force brought
by the electric motor to the steering shaft completely, by
preventing the flexure of the worm shaft of the electric motor
assist type power steering apparatus, preferably the pinion assist
type electric power steering apparatus. To attain these object,
there is provided an electric power steering apparatus comprising;
an electric motor for adding the assist steering force to the
steering system, a controller which drives said electric motor, a
rack shaft which steers a steered wheel by displacing along the
axial direction thereof, a pinion shaft which is engaged with said
rack shaft through the rack-and-pinion mechanism, a worm shaft
which is rotated by the electric motor, and a worm wheel which is
engaged with said worm shaft and is integrally arranged with the
pinion shaft, one end part of the worm shaft is joined with the
electric motor, and holding means, which holds one end part and
another end part of the worm shaft on allowing the rotation
thereof, is further arranged.
Inventors: |
Shimizu, Yasuo; (Wako-shi,
JP) ; Watanabe, Katsuji; (Wako-shi, JP) ;
Terada, Yasuhiro; (Wako-shi, JP) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
HONDA GIKEN KOGYO KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
18919711 |
Appl. No.: |
10/079610 |
Filed: |
February 19, 2002 |
Current U.S.
Class: |
180/444 ;
180/427 |
Current CPC
Class: |
Y10T 74/19623 20150115;
F16H 55/24 20130101; F16C 39/02 20130101; F16H 2057/0213 20130101;
B62D 5/0409 20130101; F16H 57/021 20130101; F16C 19/507 20130101;
Y10T 74/19842 20150115 |
Class at
Publication: |
180/444 ;
180/427 |
International
Class: |
B62D 005/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 5, 2001 |
JP |
2001-060266 |
Claims
What is claimed is:
1. An electric power steering apparatus comprising; an electric
motor for adding the assist steering force to a steering system, a
controller which drives said electric motor, a rack shaft which
steers a steered wheel by displacing along the axial direction
thereof, a pinion shaft which is engaged with said rack shaft
through a rack-and-pinion mechanism, a worm shaft which is rotated
by the electric motor, and a worm wheel which is engaged with said
worm shaft and is integrally arranged with the pinion shaft, one
end part of the worm shaft is joined with the electric motor, and
holding means, which holds one end part and another end part of the
worm shaft on allowing the rotation thereof, is further
arranged.
2. An electric power steering apparatus according to claim 1,
wherein said holding means is composed of a plurality of ball
bearings which hold one end part of the worm shaft, and a plurality
of ball bearings which hold the another end part of the worm
shaft.
3. An electric power steering apparatus according to claim 1,
wherein said holding means is composed of a plurality of ball
bearings which hold the one end part of the worm shaft, and a
needle bearing which holds another end part of the worm shaft.
4. An electric power steering apparatus comprising; an electric
motor for adding the assist steering force to a steering system, a
controller which drives said electric motor, a rack shaft which
steers a steered wheel by displacing along the axial direction
thereof, a pinion shaft which is engaged with said rack shaft
through a rack-and-pinion mechanism, a worm shaft which is rotated
by the electric motor, a worm wheel which is engaged with said worm
shaft and is integrally arranged with the pinion, end part holding
means which holds the one end part of the worm shaft on allowing
the rotation of the worm shaft, and center supporting means which
holds the center part in the longitudinal direction of the worm
shaft on allowing the rotation of the worm shaft, one end part of
said worm shaft is joined with the electric motor.
5. An electric power steering apparatus according to claim 4,
wherein said center supporting means has urging means which gives
the urging force towards the engaging part between the worm shaft
and the worm wheel from the opposite direction with respect to the
engaging part.
6. An electric power steering apparatus according to claim 5,
wherein said center supporting means has a first roller and a
second roller which are touched to the worm shaft and press the
worm shaft toward the engaging part between the worm shaft and the
worm wheel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electric motor assist
type power steering apparatus, which assists the steering effort of
a driver by making the electric motor power act on a steering
system directly.
[0003] 2. Prior Art
[0004] An electric motor assist type power steering apparatus
(hereinafter defined as an electric power steering apparatus)
assists the steering force of a driver by making use of the driving
force of an electric motor directly. A vehicle, on which an
electric power steering apparatus is mounted, is widely spreads,
and according to the electric poser steering apparatus, since a
movement of the steering becomes light, a driver operates the
steering without strong force.
[0005] As an example of the electric power steering apparatus, a
pinion assist type electric power steering apparatus, in which a
worm shaft and a worm wheel are used as the means for transmitting
the driving force of an electric motor, is known. The electric
power steering apparatus, disclosed in the Japanese patent
unexamined patent publication H11-43062, is one example
thereof.
[0006] In this electric power steering apparatus, as shown in FIG.
8, an electric motor 51 for adding an assist steering force to a
steering shaft, which is rotated by the operation of the steering,
is provided. The worm shaft 52 is connected to the electric motor
51. A pinion shaft 53 is joined with the steering shaft. The worm
wheel 54, which is engaged with a worm gear 52A of the worm shaft
52, is fixed to a pinion shaft 53 so that it will be in the coaxial
location with respect to the pinion shaft 53.
[0007] Both end parts 52B and 52C of the worm shaft 52 are held by
ball bearings 55 and 56, respectively. The assist steering force
brought by the electric motor 51 is add to the pinion shaft 53
through the worm gear 52A and the worm wheel 54 which are engaged
together. By adding this assist steering force, the steering force
required for steering operation of a driver is decreased.
[0008] In the electric power steering apparatus 50 disclosed in the
above described Japanese unexamined patent application, however,
both end parts of the worm shaft 52 are rotatably held only by the
ball bearing 55 and 56 with backlash.
[0009] Since the flexural rigidity (flexural resistance) of the
worm shaft 52 is not so high, the flexure of the worm shaft 52
tends to be arisen. When the steering is turned back in the other
way while turning in the one direction, since the steering torque
sensed by the torque sensor (not shown) decreases, the electric
motor 51 is controlled so that the assist steering force will be
decreased.
[0010] In this case, the steering must be turned back with smoothly
by rotating the electric motor 51 through the worm wheel 54 and
worm shaft 52. If the flexure is arising on the worm shaft 52,
however, since the bending moment affected to the rotation shaft of
the worm gear 52A is decreased by the decreasing of the assist
steering force brought by the electric motor 51, the restorative
deformation is arisen for correcting the flexure.
[0011] Since this restorative deformation acts as an undesirable
force and inhibits the rotation of the worm gear 52A, the rotation
force from the worm wheel 54 is not smoothly transmitted to the
electric motor 51. Thus, the mismatch on the suitable relationship
among the torque sensor (not shown), the control unit, and the
electric motor 51 is arisen. When the moment of the inertia is add
thereto, mismatch is further promoted. Then, the turning back of
the steering is disturbed and thus the response of the steering
becomes worse.
[0012] In the electric power steering apparatus 50, moreover, the
clearance which exceeds a predetermined clearance value may be
arose between the worm gear 52A and the worm wheel 54 as the
occurrence of the flexure of the worm shaft 52. When such clearance
arises, the dispensable backlash between the worm gear 52A and the
worm wheel 54 becomes larger. Thus, the assist steering force
brought by the electric motor 51 cannot be transmitted to the
steering shaft completely.
[0013] These disadvantages caused by the flexure of the worm shaft
52 will be remarkable when the assist steering force brought by the
electric motor 51 becomes large.
SUMMARY OF THE INVENTION
[0014] This is therefore, the present invention aim at providing
the electric motor assist type power steering apparatus, preferably
the pinion assist type electric power steering apparatus, which can
prevent the aggravation of the feeling of the steering by
preventing the flexure of the worm shaft, and which can transmit
the assist steering force of the electric motor to the steering
shaft completely.
[0015] For attaining these problems, there is provided an electric
power steering apparatus comprising; an electric motor for adding
the assist steering force to the steering system, a controller
which drives said electric motor, a rack shaft which steers a
steered wheel by displacing along the axial direction thereof, a
pinion shaft which is engaged with said rack shaft through the
rack-and-pinion mechanism, a worm shaft which is rotated by the
electric motor, and a worm wheel which is engaged with said worm
shaft and is integrally arranged with the pinion shaft, one end
part of the worm shaft is joined with the electric motor, and
holding means, which holds one end part and another end part of the
worm shaft on allowing the rotation thereof, is further
arranged.
[0016] In the electric power steering apparatus according to the
present invention, one end part and another end part of the worm
shaft are held without play. The worm shaft, in the conventional
manner, is held with play, thus the flexural rigidity is not so
high and the flexure of the worm shaft is easily arisen. On the
other hand, the worm shaft, in the present invention, is held
without play, thus the worm shaft can be held with high flexural
rigidity.
[0017] Accordingly, by preventing the occurrence of the flexure of
the worm shaft, not only the occurrence of the mismatch caused by
the flexure of the worm shaft at the time of turning back of the
steering but also the occurrence of the aggravation of the steering
feeling are prevented. Thus, the certain transmission of the
steering force brought by the electric motor to the pinion shaft
can be achieved.
[0018] In the electric power steering apparatus, preferably, said
holding means is composed of plural ball bearings which hold one
end part of the worm shaft, and plural ball bearings which hold the
another end part of the worm shaft.
[0019] According to this electric power steering apparatus, both
end parts of the worm shaft are held without play by plural of ball
bearings. Thus, the holding of the worm shaft can be carried out on
keeping the rotating condition at the both ends of the worm shaft
into the smooth condition. And also the holding of the worm shaft
can be carried out using ball bearings, which are general-purpose
parts without using the specific parts. Therefore, the contribution
to a cost reduction may be attained.
[0020] In the electric power steering apparatus, preferably, said
holding means is composed of plural ball bearings which hold the
one end part of the worm shaft, and a needle bearing which holds
another end par of the worm shaft.
[0021] According to this electric power steering apparatus, one end
part side of the worm shaft joined with the electric motor is held
by the plural of ball bearings. Since one end part of the worm
shaft is joined with the electric motor, flexural rigidity in the
one end part of the worm shaft is comparatively high, and that of
in the another end part becomes low a little.
[0022] In the present electric power steering apparatus, therefore,
another end part of the worm shaft is held by a needle bearing
without play. When the worm shaft is held by the needle bearing
without play, since the flexural resistance of the worm shaft in
the diameter direction is higher than the worm shaft held by the
plural of ball bearings, the flexural rigidity along the worm gear
whole may be higher. Thus, the occurrence of the flexure of the
worm shaft is thus prevented, and also the occurrence of the
feeling gap between in the case the steering is turned back in the
anticlockwise direction and in the case the steering is turned back
in the clockwise direction can be decreased. Thus, not only the
prevention of the aggravation of steering feeling but also the
certain transmission of the steering force brought by the electric
motor 7 to the pinion shaft 3 are achieved.
[0023] In the present invention, furthermore, there is provided an
electric power steering apparatus comprising; an electric motor for
adding the assist steering force to the steering system, a
controller which drives said electric motor, a rack shaft which
steers a steered wheel by displacing along the axial direction
thereof, a pinion shaft which is engaged with said rack shaft
through the rack-and-pinion mechanism, a worm shaft which is
rotated by the electric motor, a worm wheel which is engaged with
said worm shaft and is integrally arranged with the pinion shaft,
end part holding means which holds the one end part of the worm
shaft on allowing the rotation of the worm shaft, and center
supporting means which holds the center part in the longitudinal
direction of the worm shaft on allowing the rotation of the worm
shaft, wherein one end part of said worm shaft is joined with the
electric motor.
[0024] According to this electric power steering apparatus, about
the center part in the longitudinal direction of the worm shaft is
supported on allowing the rotation of the worm shaft. Thus, the
worm shaft can be made into the rotatable condition, and the
occurrence of the flexure of the worm shaft can be prevented. This
is therefore, the aggravation of the feeling of the steering is
prevented, and the steering force brought by the electric motor can
be transmitted to the pinion shaft certainly. According to the
center supporting means, the worm shaft is held without arranging
the holding means at one end part of the worm shaft, the assembling
efficiency of the apparatus as a whole is improved.
[0025] In the electric power steering apparatus, preferably, said
center supporting means has urging means which gives the urging
force towards the engaging part between the worm shaft and the worm
wheel from the opposite direction with respect to the engaging
part.
[0026] According to the present invention, the urging means which
urges the worm shaft to the engaging part side with respect to the
worm wheel is arranged. Since the flexure of the worm shaft is
prevented, and the worm shaft is pressed to the worm wheel with
sufficient force, the clearance between the worm shaft and the worm
wheel is maintained within the predetermined range. Thus, the
occurrence of the unpleasant backlash between the worm gear and the
worm wheel can be prevented, and the certain transmission of the
rotation of the worm shaft to the worm wheel can be achieved.
[0027] In the electric power steering apparatus, preferably, said
center supporting means has a first roller and a second roller
which are touched with the worm shaft and press the worm shaft
toward the engaging part between the worm shaft and the worm
wheel.
[0028] According to the present invention, the first roller and the
second roller, which are fitted with the worn shaft, is applied to
the engaging part between the worm shaft and the worm wheel. Thus,
the displacement in the ups-and-downs directions of the worm shaft
is restricted, and the worm shaft is applied to the engaging part
between the worm shaft and the worm wheel. Since the roller is
used, the supporting mechanism with slightest fiction can be
obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a whole block diagram of the electric power
steering apparatus according to the first preferred embodiment of
the present invention.
[0030] FIG. 2 is a plan view of the substantial part of the
electric power steering apparatus according to the first preferred
embodiment of the present invention.
[0031] FIG. 3 is a sectional view along the line X-X in FIG. 2.
[0032] FIG. 4A is an explaining view of the model of the beam both
ends part of which are held without play, and the bending moment
applied to the beam.
[0033] FIG. 4B is an explaining view of the model of the beam both
ends part of which are held with play, and the bending moment
applied to the beam.
[0034] FIG. 2 is a plan view of the substantial part of the
electric power steering apparatus according to the second preferred
embodiment of the present invention.
[0035] FIG. 6 is a plan view of the substantial part of the
electric power steering apparatus according to the third preferred
embodiment of the present invention.
[0036] FIG. 6 is a sectional view along the line Y-Y in FIG. 2.
[0037] FIG. 8 is a plan exploded view of the substantial part of
the conventional electric power steering.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] The preferred embodiments of the present invention will now
be described by referring to the attached drawings. FIG. 1 is a
block diagram of the electric power steering apparatus according to
the present invention. FIG. 2 is a plan view of the principal part
of the electric power steering apparatus. FIG. 3 is a sectional
view along the line X-X in FIG. 2.
[0039] As shown in FIG. 1, an electric power steering apparatus 1
according to the present invention has a steering 2. The steering 2
is connected to a pinion shaft 4 through a steering shaft 3. A
torque sensor 5 and a torque transmitter 6 are attached to the
pinion shaft 4. The torque sensor 5 detects the steering torque add
to the steering system. The torque transmitter 6 is an assistor,
and connected to an electric motor 7, which adds the assists
steering force to the steering system.
[0040] A pinion 4A, arranged at the bottom part of the pinion shaft
4, is engaged with a gear rack 8A provided on a rack shaft 8. In
this construction, the rotation of the pinion shaft 4 is converted
into the displacement in the longitudinal direction with respect to
the rack shaft 8, and then a steered wheel 9 and 9 are steered. The
torque sensor 5 is connected to a control unit 10, and outputs the
toque signal to the control unit 10. The control unit 10 computes
the assist steering force using at least the torque signal T
outputted form the torque sensor 5, and outputs the electric motor
control signal VO to the electric motor 7, and thus the electric
motor 7 is controlled.
[0041] As shown in FIG. 2 and FIG. 3, the torque transmitter 6 has
a worm wheel 11, which is fixed to the pinion shaft 4 so that it
might be in the coaxial location with respect to the pinion shaft
4. A worm shaft 12 is joined to the rotation shaft of the electric
motor 7 through the coupling and the like. A worm gears 12A
provided on the worm shaft 12 is engaged with the worm wheel
11.
[0042] When the worm shaft 12 is rotated by the actuation of the
electric motor 7, the worm wheel 11 engaged with the worm gears 12A
is rotated, and thus the pinion shaft 4 is rotated along with the
rotation of the worm wheel 11 through the mechanism such as a
planetary gear and the like. The assist steering force (steering
force) brought by the electric motor 7 is transmitted to the pinion
shaft 4, and then transmitted to the steering shaft 3 through the
pinion shaft 4.
[0043] One end part 12B of the worm shaft 12 is held by a first
ball bearing 14A and a second ball bearing 14B, which are arranged
in the adjoining location along the longitudinal direction of the
worm shaft 12, on allowing the rotation of the worm shaft 12.
[0044] The ball bearings 14A and 14B are a holding means, which
holds the one end part 12B of the worm shaft 12 with sufficient
flexural rigidity. In other words, the holding means restricts the
flexure of the worm shaft 12.
[0045] Another end part 12C of the worm shaft 12, furthermore, is
held by a first ball bearing 15A and a second ball bearing 15B,
which are arranged in the adjoining location along the longitudinal
direction of the worm shaft 12, on allowing the rotation of the
worm shaft 12.
[0046] The ball bearing 15A and 15B are also a holding means, which
holds the one end part 12C of the worm shaft 12 with sufficient
flexural rigidity. In other words, the holding means restricts the
flexure of the worm shaft 12.
[0047] The location interval L1 between the ball bearing 14A and
14B and the location interval L2 between the ball bearing 15A and
15B are same. The location interval L1 and the location interval L2
are established as long as possible so that it can restrict the
flexure of the worm shaft 12 efficiently.
[0048] The explanation about the function and the operation of the
electric power steering apparatus having the above-described
construction will be carried out.
[0049] When the driver operates the steering 2 shown in FIG. 1, the
torque sensor 5 detects the steering torque. The steering torque
detected by the torque sensor 5 is output to the control unit 10 as
a torque signal T.
[0050] In the control unit 10, the assist steering force, which is
brought by the electric motor 7 and add to the steering system, is
computed using at least the steering torque represented by the
torque signal T on considering the factors such as traveling speed
and the steering angle.
[0051] Based on this computed assist steering force, the electric
motor control signal Vo is output to the electric motor 7 from the
control unit 10.
[0052] The electric motor 7 is driven by the electric motor control
signal Vo, and rotates the worm shaft 12 of shown in FIG. 2. One
end part 12B of the worm shaft 12 is held by the ball bearing 14A
and 14B while the worm shaft 12 is rotating. Another end part 12C
of the worm shaft 12 is also held by the ball bearing 15A and 15B.
Thus, both end parts of the worm shaft 12 is in the held condition
by holding both end part 12B and 12C of the worm shaft 12 on
allowing the rotation of the worm shaft.
[0053] The explanation about the flexural resistance of the worm
shaft 12 will be carried out on considering the worm shaft 12 as a
beam.
[0054] FIG. 4A is an explaining view of the bending moment in the
case that the force P is applied to the center in the longitudinal
direction of a beam from the upper direction, wherein both end
parts of the beam are rigidly held without play (play means it has
a loose fit).
[0055] FIG. 4A is an explaining view of the bending moment in case
that the force P is applied to the center in the longitudinal
direction of a beam from the upper direction, wherein both end
parts of the beam are held with play (play means it has a loose
fit).
[0056] As shown in FIG. 4A, in the case of the beam H, which has a
length l and both end parts HA and HB of which are rigidly held
without play, the bending moment add thereto is Pl/8.
[0057] As shown in FIG. 4B, in the case of the beam H, which has a
length l and both end parts HA and HB of which are held with play,
the bending moment add thereto is Pl/4.
[0058] The bending moment applied to the beam H, both end parts HA
and HB of the which are rigidly held without play, becomes one half
in the case that both end parts HA and HB of the beam H are
supported with play. Thus, when both end parts HA and HB of the
beam H are rigidly held without play, the bending moment might be
smaller than the case where both end parts HA and HB are supported
with play.
[0059] When the force P is applied to the center in the
longitudinal direction of the beam H from the upper direction,
wherein both end parts of which HA and HB are rigidly held without
play, the maximum flexural amount (.delta. max) of the beam H is
formulated as formula (1).
.delta. max=Pl.sup.3/192EI.sub.z (1)
[0060] P: the force added to the beam H
[0061] l: the length of the beam H
[0062] E: Young's modulus
[0063] I.sub.z: geometrical moment of inertia
[0064] On the contrarily, when the force P is applied to the center
in the longitudinal direction of the beam H from the upper
direction, wherein both end parts of which HA and HB are held with
play, the maximum flexural amount (.delta. max) of the beam H is
formulated as formula (2).
.delta. max=Pl.sup.3/48EI.sub.z (2)
[0065] P: the force applied to the beam H
[0066] l: the length of the beam H
[0067] E: Young's modulus
[0068] I.sub.z: geometrical moment of inertia
[0069] Therefore, the flexural amount of the beam H, wherein both
end parts are rigidly held without play becomes to one fourth with
respect to the case where both end parts are held with play. As
described above, when both end parts HA and HB of the beam H are
rigidly held without play, the flexural amount of the beam H can be
smaller than that of the beam H, both end parts of which are held
with play. The beam with sufficient flexural rigidity and with high
flexure resistance can be supplied when both end parts of the beam
are held without play.
[0070] Therefor, when both end parts of the beam H are rigidly
held, the holding of the beam member can be carried out with
sufficient rigidity than the case where the both end parts are
supported with play, and thus the maximum flexural amount of the
beam H can be smaller.
[0071] As for the electric power steering apparatus 1 according to
the present preferred embodiment, the worm shaft 12 is rigidly held
by the ball bearing 14A, 14B, 15A and 15B without play. Since the
same reason as described in the case of beam H can be applicable,
the worm shaft 12 according to the present invention can be held
with sufficient flexural rigidity as compared to the conventional
holding manner.
[0072] When the force P is applied to the center in the
longitudinal direction of the worm shaft 12 as a result of the
actuation of the electric motor 7, therefore, the bending moment
becomes to one half and the maximum bending amount becomes one
fourth. Thus, the flexure of the worm shaft 12 is efficiently
prevented.
[0073] Then, the occurrence of the mismatch, which is caused by the
flexure of the worm shaft at the time of the steering wheel is
turning back in the reverse direction, and the aggravation of the
steering responsibility in the electric power steering apparatus 1
are sufficiently prevented. Thus, the transmission of the assist
steering force brought by the electric motor 7 to the steering
shaft 3 can be achieved.
[0074] In the present embodiment, furthermore, due to the weight of
the electric motor 7, the difference between the flexural rigidity
at one end part 12B and at the another end part 12C of the worm
shaft 12 may be arisen.
[0075] When the rotation axis of the electric motor 7 and the worm
shaft 12 are joined firmly, for example, the flexural rigidity at
the one end part 12B of the worm shaft 12 is higher than another
end part 12C of the worm shaft 12 (flexural angle becomes
smaller).
[0076] If the rotation axis of the electric motor 7 and the worm
shaft 12 are joined firmly, it is acceptable that the location
interval L2 between the ball bearing 15A and 15B, which support
another end part 12c of the worm shaft 12, is established wider
than the location interval L1 between ball bearing 14A and 14B.
[0077] To be more precise, the flexural rigidity of another end
part 12c side can be stronger than that of one end part 12B side,
by establishing the interval between the ball bearing 15A and 15B
wider than that of between the ball bearing 14A and 14B. Therefore,
since one end part 12B and another end part 12C are rigidly held
with the uniform flexural rigidity depending on the strength of the
connecting part between the rotation axis of the electric motor 7
and the worm shaft 12, the prevention of the flexure of the worm
shaft 12 can be achieved more certainly.
[0078] The second preferred embodiment according to the present
invention will be described. FIG. 5 is a plan sectional view
showing a substantial part of the electric power steering apparatus
according to the present invention.
[0079] In an electric power steering apparatus 20 according to the
present preferred embodiment, only the construction of the torque
transmitter is differing from the electric power steering apparatus
1. Thus, in the following explanation, the explanation is mainly
carried out about the different components, and the same components
as that of explained in the first embodiment is emitted and
indicates as the same symbol.
[0080] As shown in FIG. 5, a torque transmitter 21 according to the
present second preferred embodiment of the electric power steering
apparatus 20, has a worm wheel 11 fixed to the pinion shaft 4 so
that it might be in the coaxial location with respect to the pinion
shaft 4.
[0081] A worm gear 12 is joined to the electric motor 7. The worm
gears 12A provided to the worm shaft 12 is engaged with the worm
wheel 11.
[0082] When the worm shaft 12 is rotated by the actuation of the
electric motor 7, the worm wheel 11 engaged with the worm gears 12A
is rotated, and then the pinion shaft 4 is rotated along with the
rotation of the worm wheel 11. The assist steering force brought by
the electric motor 7 is transmitted to the pinion shaft 4. These
compositions are same as that of disclosed in the first preferred
embodiment.
[0083] One end part 12B of the worm shaft 12 is held by the ball
bearing 14A and 14B which are arranged in the adjoining location
along the longitudinal direction of the worm shaft 12.
[0084] On the other hand, another end part 12C of the worm shaft 12
is held by a needle bearing 22 on allowing the rotation around the
axis. The electric power steering apparatus 20 according to the
present preferred embodiment differs in that the another end part
12C of the worm shaft 12 is supported without play on allowing the
rotation.
[0085] As for the worm shaft 12 in the electric power steering
apparatus 20 according to the present preferred embodiment, one end
part 12B of the worm shaft 12 is held without play by the two of
ball bearings 14A and 14B, and another end part 12C of the worm
shaft 12 is held without play by the needle bearing 22.
[0086] As for the needle bearing 22, since needle rollers (located
at inner-side and outer-side in figure) are contacting with the
worm shaft 12 along the longitudinal direction of the worm shaft
12, wide range of the worm shaft 12 is held by the needle
roller.
[0087] Thus, flexural resistance in the diameter direction at the
another end part 12C of the worm shaft 12 where is supported by the
needle bearing 22 is higher than one end part. Therefore, since
another end part 12C is held by the needle bearing 22, the flexural
rigidity at the another end part 12C of the worm gear 12 is also
higher than the one end part 12B where the worm gear 12 is held by
the ball bearing 14A and 14B.
[0088] The flexural rigidity at one end part 12B and another end
part 12C of worm shaft 12 can be uniform by holding the another
ends part 12C using the needle bearing 22, which gives the superior
flexural resistance, even if the rigidity at the one ends part 12B
becomes high as a result of the firmly connection between the
rotating shaft of the electric motor 7 and the worm shaft 12.
[0089] The occurrence of the flexure of the worm shaft is thus
prevented, and also the occurrence of the feeling gap between in
the case the steering is turned back in the anticlockwise direction
and in the case the steering is turned back in the clockwise
direction can be decreased. Thus, not only the prevention of the
aggravation of steering feeling but also the certain transmission
of the steering force brought by the electric motor 7 to the pinion
shaft 3 are achieved.
[0090] The third preferred embodiment of the present invention will
be explained. FIG. 6 is a plan sectional view of the substantial
part of the electric power assist type steering apparatus according
to the present invention. FIG. 7 is sectional view along the line
Y-Y in FIG. 6.
[0091] In the electric power steering apparatus 30 according to the
present preferred invention, only the construction of the torque
transmitter is differing from the electric power steering apparatus
1. Thus, in the following explanation, the explanation is mainly
carried out about the different components, and the same components
as that of explained in the first embodiment is emitted and
indicates as the same symbol.
[0092] As shown in FIG. 6, a torque transmitter 21 according to the
present second preferred embodiment of the electric power steering
apparatus 30, has a worm wheel 11 fixed to the pinion shaft 4 so
that it might be in the coaxial condition with the pinion shaft
4.
[0093] The worm gear 12 is joined to the electric motor 7, and a
worm gear 12A provided thereto is engaged with the worm wheel
11.
[0094] When the worm shaft 12 is rotated by the actuation of the
electric motor 7, the worm wheel 11 engaged with the worm gear 12A
is rotated, and then the pinion shaft 4 is rotated along with the
worm wheel 11. The assist steering force brought by the electric
motor 7 is transmitted to the pinion shaft 4. These compositions
are same as that of disclosed in the first and second preferred
embodiment.
[0095] One end part 12B of the worm shaft 12 is held by a ball
bearing 32 in the condition the rotation of the worm shaft 12 might
be allowed. Another end part 12C is also held by a ball bearing 33
in the condition where the rotation of the worm shaft 12 might be
allowed.
[0096] A central holding means 35 is arranged at the almost central
part in the longitudinal direction of the worm shaft 12. The
central holding means 35 is positioned so that the worm shaft 12
might be sandwiched between the worm wheel 11 and the central
holding means 35, and has a urging means 34 which crowds the worm
shaft 12 toward the direction of the worm wheel 11.
[0097] According to this urging means 34, the worm shaft 12 is
pressed toward the worm wheel 11 from the opposite direction side
with respect to the engaging part where the worm gear 12A and worm
wheel 11 are engaged together. This urging means 34 is arranged for
pressing the worm shaft 12 to the engaging part of the worm wheel
11, and is composed of a spring 36, an upper roll 37, a lower roll
38, and a roller holder 39 (see FIG. 7).
[0098] As shown in FIG. 7, the urging means 34 has the upper roll
37 and the lower roll 38 which are arranged at the opposite side
with respect to the engaging part where the worm wheel 11 and the
worm gear 12A of the worm shaft 12 are engaged together. The urging
means 34 also has a roller holder 39, which rotatably supports the
upper roll 38 and the lower roll 39, and the spring 36, which press
the roller holder 39 towards the worm shaft 12 urgently.
[0099] The upper roll 37 and the lower roll 38 are fit with the
worm gear 12A, respectively, and transmit the urgent force brought
by the spring 36 to the worm gear 12A. The rotation shafts of the
upper roll 37 and the lower roll 38 are supported by the roller
folder 39 and thus the movement in the ups-and-downs directions
thereof is restricted.
[0100] In the electric power steering apparatus 30 according to the
present preferred embodiment, about the center part in the
longitudinal direction of the worm shaft 12 is supported by the
center holding means 35. The flexural degree of the worm shaft 12,
conventionally, tends to be maximum at the central part in the
longitudinal direction of the worm shaft 12. As for the present
preferred embodiment, since the worm shaft 12 is supported by the
center holding means 35, the occurrence of the flexure of the worm
shaft 12 is efficiently prevented. As a result of this prevention,
the aggravation arose at the time of turning back of the steering
is prevented, and thus the prevention of the aggravation of the
steering feeling and the certain transmission of the steering force
by the electric motor to the pinion shaft can be achieved.
[0101] In the present invention, the central part between one end
part and the another end part of the worm shaft 12 is supported,
the scattering in the flexural resistance in the longitudinal
direction of the worm shaft 12 can be smaller. Thus, the gaps in
the steering feeling depending on the turning direction of the
steering can be smaller.
[0102] As for the present invention, furthermore, since the center
holding means 35 has the urging means 34, the urgent force brought
by the spring 36 is transmitted to the worm shaft 12 through the
upper roll 37 and the lower roll 38. Accordingly, the clearance
between the worm gear 12A and the worm wheel 11 is maintained
within the predetermined clearance even if the clearance, which
exceeds a predetermined clearance value, come close to arising as a
result of the occurrence of slight flexure of the worm gear 12.
[0103] The worm gear 12A and the worm wheel 11 are certainly
engaged together by the center holding means 35, the unpleasant
backlash between the worm gear 12A and the worm wheel 11 thus can
be prevented. Then, the transmission of the assist steering force
brought by the electric motor 7 to the worm wheel 11 through the
worm shaft 12 can be achieved certainly.
[0104] Since the urgent force brought by the spring 36 is
transmitted to the worm shaft 12A through the upper roll 37 and the
lower roll 38 which are being rotatable, the rotation of the worm
shaft 12 is carried out without any restriction.
[0105] The displacement in the ups-and-downs directions of the
upper roll 37 and the lower roll 38, which are applied to the worm
shaft 12, are restricted, furthermore, the displacement in the
ups-and-downs directions of the worm gear 12 is also prevented.
[0106] According to this prevention, the flexure in the
ups-and-downs directions of the worm gear 12 is also prevented.
Thus, the aggravation of the steering feeling is prevented, and
also the steering force, which is brought by the electric motor, is
certainly transmitted to the pinion shaft. According to the
supporting mechanism of the present invention, since the worm gear
12 supported by the upper roll 37 and lower roll 38, the supporting
mechanism with reduced unpleasant friction can be supplied.
[0107] In the present preferred embodiment, both end parts of the
worm gear 12 are held by the ball bearings 32 and 32, but the
holding manner of the worm gear 12 is not restricted to this case.
The holding manner, for example, in which the worm gear 12 is held
without the ball bearing arranged at another end part of the worm
gear can be applicable as long as the flexural resistance brought
by the center holding means is acceptable.
[0108] In the present preferred embodiment, the explanation about
the electric power steering apparatus, which assist the steering
effort of the driver by adding the assist steering force brought by
the electric motor in addition to the steering force brought by the
driver's operation, is carried out.
[0109] The application of the present invention is not restricted
to the above-described case. The application to the another type of
construction may be acceptable as long as the it has a construction
that the diving force brought by the electric motor is add to the
pinion shaft, which is joined to the rack shaft and steers the
steering wheel. As an example of this, the steer-by-wire mechanism
which steers the steered wheel only by the driving force, which is
brought by the electric motor and is controlled by the electric
signal, and the four-wheel-steering mechanism and the like are
considerable.
[0110] As described above, in the present invention, the worm shaft
12 is held with sufficient flexural rigidity by holding the worm
shaft without play. According to this invention, since the flexure
of the worm shaft 12 is prevented, the aggravation caused by the
flexure of the worm shaft 12 at the time of turning back of the
steering is prevented. As a result of this prevention, the
aggravation of the steering feeling and the certain transmission of
the steering force, which is brought by the electric motor, to the
pinion shaft can be achieved.
[0111] In the present invention, one end part and another end part
of the worm shaft are held by plural of ball bearings,
respectively. According to this invention, the worm shaft is held
without play on maintaining the smooth rotation of the worm gear.
Since the ball bearing which are general-purpose components is
used, furthermore, it can contribute to a cost reduction.
[0112] In the present invention, both end parts of the worm shaft
are held with the uniform flexural rigidity by holding the another
end part side, in which the flexural rigidity is low a little, by
the needle bearing. According to this invention, the flexure of the
worm shaft is certainly prevented and also the occurrence of the
feeling gap between in the case the steering is turned back in the
anticlockwise direction and in the case the steering is turned back
in the clockwise direction can be decreased. the certain
transmission of the steering force brought by the electric motor 7
to the pinion shaft 3 is achieved.
[0113] In the present invention, the occurrence of the flexure of
the worm shaft can be prevented while the worm shaft is made into
the rotatable condition. According to this invention, the
aggravation of the steering feeling and the certain transmission of
the steering force brought by the electric motor to the pinion
shaft can be achieved.
[0114] In the present invention, since the worm shaft is pressed to
the engaging part between the worm shaft and the worm wheel by the
urgent force of the urging means with the suitable force, the
clearance between the worm shaft and the worm wheel can be
maintained within the predetermined ranges. According to the
present invention, since the occurrence of the backlash between the
worm gear and the worm wheel is prevented, the rotation of the worm
shaft is certainly transmitted to the worm wheel.
[0115] In the present invention, the displacement in the
ups-and-downs directions of the worm shaft is restricted. The worm
shaft is crowed toward the engaging part with worm wheel on
allowing the rotation of the worm shaft. According to the
invention, since the roller is used, the unpleasant friction with
respect to the worm gear can be reduced.
* * * * *