Machine element or mechanism – Gearing – Follow-up mechanism
Reexamination Certificate
2000-06-28
2004-07-20
Bucci, David A. (Department: 3682)
Machine element or mechanism
Gearing
Follow-up mechanism
C074S425000, C074S500000
Reexamination Certificate
active
06763738
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus in which a motor is used as a source of a steering assist force.
Steering of an automobile is carried out by transmitting rotating operation of a steering wheel disposed within a vehicle room to a steering mechanism disposed on an outside of the vehicle room for steering wheels (front wheels, in general) for steering.
FIG. 1
is a sectional view of an electric power steering apparatus of prior art and
FIG. 2
is a sectional view of a reduction mechanism and a motor portion.
As shown in
FIG. 1
, the electric power steering apparatus for the automobile has a first steering shaft
102
connected to a steering wheel
101
, a torque sensor
105
for detecting steering torque based on a relative displacement between the first steering shaft
102
and a second steering shaft
104
connected to the first steering shaft
102
through a torsion bar
103
in a rotating direction, and the reduction mechanism
109
including a worm
107
and a worm wheel
108
for increasing a rotating force of a steering assisting motor
106
driven based on a detection result of the torque sensor
105
and for transmitting the rotating force to the second steering shaft
104
. By means of the above constitution the electric power steering apparatus assists operation of the steering mechanism according to rotation of the steering wheel
101
by rotation of the motor
106
to reduce labor and a load imposed on a driver for steering.
Opposite end sides of the worm shaft
110
provided with the worm
107
and the second steering shaft
104
provided with the worm wheel
108
in shaft length directions are respectively supported by bearings
111
,
112
, and
113
,
114
and movements of the shafts in diameter directions and the shaft length directions are prevented.
If the worm
107
and the worm wheel
108
are used as described above, a distance between rotation centers of the worm shaft
110
and the worm wheel
108
is preset in assembly. In this presetting, dimensional errors of the worm
107
, the worm shaft
110
, the bearings
111
and
112
for supporting the worm shaft
110
, the worm wheel
108
, the second steering shaft
104
for supporting the worm wheel
108
, and the like cause variations in the distance between the rotation centers, backlash occurs after assembly, and noise due to the backlash is heard in the room of the automobile.
A meshing state changes with time because cogs of the worm
107
and the worm wheel
108
wear as a result of steering or because the worm wheel
108
made of synthetic resin contracts due to low temperatures during wintertime and the like and occurrence of the backlash is inevitable.
In order to reduce variations in the distance between the rotation centers in assembly, it is necessary to process parts such as the worm shaft
110
, the bearings
111
to
114
, the worm wheel
108
, and the second steering shaft
104
with small dimensional errors, measure dimensions of all the parts, select the respective parts based on the measured dimensions, and assemble the parts. Therefore, costs of processing and assembly and cost of the entire electric power steering apparatus increase. Moreover, because the movements of the assembled worm shaft
110
and worm wheel
108
in directions intersecting the rotation centers are prevented, the distance between the rotation centers cannot be adjusted and the backlash cannot be adjusted when the meshing state has changed with time.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electric power steering apparatus in which the above problems can be solved.
In an electric power steering apparatus according to a first invention for transmitting rotating force of a steering assisting motor to a worm shaft having a worm and being rotatably supported in a gear housing through a bearing and to a steering shaft provided with a worm wheel meshing with the worm and for assisting steering, the electric power steering apparatus has a bearing case provided with a holding hole in which the bearing is fitted and held, and a mechanism for decentering the bearing toward the worm wheel.
In the first invention, because the bearing with which the worm shaft is fitted can be moved toward the worm wheel, it is possible to easily set a distance between rotation centers of the worm shaft and the worm wheel without being influenced by dimensional errors of parts such as the worm shaft and to reduce costs of processing and assembly of parts as compared with the above-described prior art. Moreover, because the bearing case has the decentering mechanism, it is possible to easily provide the decentering mechanism. Because the bearing can be decentered in a state in which the bearing is fitted and held in the holding hole of the bearing case, the distance between the rotation centers can be adjusted satisfactorily when a meshing state of the worm and the worm wheel changes with time due to increase in wearing amounts of cogs of the worm and the worm wheel or contraction of the worm wheel made of synthetic resin as a result of low temperatures during wintertime and the like.
In an electric power steering apparatus according to a second invention, the decentering mechanism has an inclined face formed on an inner peripheral face of the holding hole such that the holding hole is inclined with respect to the rotation center of the worm shaft, and has an inclined contact surface provided on an outer periphery of the bearing and comes in contact with the inclined face.
In an electric power steering apparatus according to a third invention, the contact surface is provided on the outer peripheral face of a ring member fitted with and fixed to the outer periphery of the bearing.
In the second and third inventions, because of a simple structure in which the holding hole of the bearing case is inclined and the inclined contact surface is provided in association with the bearing, the structure of the decentering mechanism can be simplified to further reduce the cost.
In an electric power steering apparatus according to a fourth invention, a pair of bearings with which opposite end portions of the worm shaft are fitted respectively are provided, one of the bearings is held in the bearing case, and an elastic member for energizing the worm shaft toward the one bearing is provided on a side of the other bearing.
An electric power steering apparatus according to a fifth invention further comprises a mechanism for adjusting a deflection amount of the elastic member from outside.
In the fourth and fifth inventions, is it possible to satisfactorily prevent rattling of the worm shaft in the shaft length direction when adjusting the distance between the rotation centers of the worm shaft and the worm wheel.
In an electric power steering apparatus according to a sixth invention, the bearing case has a fitting portion rotatably fitted with the gear housing around the holding hole and the decentering mechanism decenters the holding hole with respect to the center of the fitting portion.
In an electric power steering apparatus according to a seventh invention, the decentering mechanism has a mechanism for rotating the bearing case from outside and changes a position of the worm shaft supported by the bearing fitted and held in the holding hole with respect to the worm wheel by rotating the bearing case.
In the sixth and seventh invention, because the bearing can be decentered by rotating the bearing case, it is possible to easily adjust the distance between the rotation centers in assembly. Moreover, it is possible to easily adjust the distance between the rotation centers when the meshing state of the worm and the worm wheel changes with time due to wearing of cogs of the worm and the worm wheel as a result of steering or contraction of the worm wheel made of synthetic resin as a result of low temperatures during wintertime and the like.
In an electric power steering apparatus according to an eighth invention, a pair of bearings with which opposite
Tsutsui Takashi
Watanabe Masayuki
Birch & Stewart Kolasch & Birch, LLP
Bucci David A.
Hansen Colby
Koyo Seiko Co. Ltd.
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