Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2001-05-18
2004-03-23
Morris, Lesley D. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C074S427000
Reexamination Certificate
active
06708796
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus using a motor as a source for generating steering assisting force.
An automobile is steered by transmitting an operation for rotating a steering wheel provided in a vehicle compartment to a steering mechanism provided outside the vehicle compartment for turning a wheel (generally a front wheel) for steering.
FIG. 1
is a sectional view showing a conventional electric power steering apparatus and
FIG. 2
is a sectional view showing a speed reducing mechanism portion. For example, as shown in
FIG. 1
, an electric power steering apparatus for an automobile comprises a first steering shaft
101
having an upper end coupled to a steering wheel
100
for steering, a second steering shaft
103
having an upper end coupled coaxially to a lower end of the first steering shaft
101
through a torsion bar
102
and a lower end coupled to a steering mechanism connected to a wheel, a torque sensor
104
for detecting a torque applied to the first steering shaft
101
by the rotation of the steering wheel
100
through a twist generated on the torsion bar
102
, a steering assistance motor
105
to be driven based on the result of detection of the torque sensor
104
, and a speed reducing mechanism having a worm
106
and a worm wheel
107
which are connected to an output shaft of the motor
105
and serve to reduce the speed of the rotation of the output shaft and to transmit the rotation to the second steering shaft
103
, and the operation of the steering mechanism corresponding to the rotation of the steering wheel
100
is assisted by the rotation of the motor
105
, thereby relieving a driver's labor and burden for steering.
The worm
106
constituting the speed reducing mechanism is supported in a fit hole of a housing
110
through a pair of rolling bearings
108
and
108
as shown in
FIG. 2
, and the second steering shaft
103
provided with the worm wheel
107
is supported in the fit hole of the housing
110
through a pair of rolling bearings
109
and
109
so that the movement of the worm
106
and the worm wheel
107
in radial and axial directions is blocked.
In the steering apparatus using the worm
106
and the worm wheel
107
, thus, when the backlash amount of an engagement portion is large, a backlash sound is generated so that the backlash sound leaks into the compartment of the automobile. In order to reduce the backlash amount of the engagement portion of the worm
106
and the worm wheel
107
and to eliminate a beating sound through the backlash, the worm
106
, the worm wheel
107
, the rolling bearings
108
and
109
, the second steering shaft
103
and the housing
110
which are processed such that a distance between the rotation centers of the worm
106
and the worm wheel
107
is coincident with a distance between the centers of the fit holes in which the rolling bearings
108
and
109
are fit within an allowance are selected and assembled. A long time is required for the assembly. Furthermore, while a high load is applied to rotate the worm
106
and the worm wheel
107
and a loading work for adapting the engagement portion after the assembly, a long time is required for the loading work so that an improvement has been demanded.
Moreover, the wear of the teeth of the worm
106
and the worm wheel
107
is increased, the atmospheric temperature of the worm wheel
107
formed of a synthetic resin is changed or the worm wheel
107
absorbs moisture so that the backlash amount is increased. Furthermore, there has been a problem in that the torque of the engagement portion is disordered and stock is increased through the selective assembly described above.
The present applicant has proposed an electric power steering apparatus (Japanese Patent Application Laid-Open No. 2000-43739) in which moving means (pressing means) such as an elastic body for moving, in a radial direction, a shaft on the opposite side to a motor in a worm having a motor side shaft rotatably supported in a housing through a rolling bearing, moving the bearing in abutment on the peripheral surface of a bearing fitted in the shaft and pressing the worm toward a worm wheel is provided and a distance between the rotation centers is regulated by operating the pressing means so that a backlash amount can be adjusted.
Moreover, the Japanese Patent Application Laid-Open No. 2000-43739 has also described an electric power steering apparatus in which pressing means for moving, in a radial direction, a motor side shaft of a worm having a shaft on the opposite side to the motor rotatably supported on a housing through a rolling bearing, moving the bearing in abutment on the peripheral surface of a bearing fitted in the shaft and pressing the worm toward a worm wheel is provided, a coupling portion of the motor side shaft of the worm and the output shaft of the motor is coupled through a constant velocity joint so that the worm can be slid around a bearing portion having the shaft on the opposite side to the motor supported thereon, the distance between the rotation centers is regulated by operating the pressing means so that a backlash amount can be adjusted.
On the other hand, as described in Japanese Utility Model Publication No. 2-8124 (1990), there has been known a worm type speed reducing machine in which pressing means having an insertion hole for inserting a bearing fitted in a shaft provided on one of ends of a worm and capable of moving in the radial direction of the shaft is provided such that the worm is pressed toward a worm wheel through the pressing means or pressing means having a pair of rollers abutting on two peripheral positions of the worm and capable of moving in the radial direction of the worm such the that worm is pressed toward the worm wheel through the pressing means.
However, the conventional pressing means is formed to be smoothly moved in a guide hole provided in a housing accommodating a worm, while the tooth trace of the worm wheel
107
of the speed reducing mechanism or the like is twisted in a rotation direction with respect to a rotation center line. Accordingly, when a rotation torque is to be applied from the worm
106
to the worm wheel
107
, in other words, the steering is to be assisted through the rotation of the motor
105
, a comparatively great component of force is generated such that the worm
106
is moved in a radial direction along the tooth trace of the worm wheel
107
so that the worm
106
is strongly pressed in the radial direction through the component of force. For this reason, in the conventional electric power steering apparatus having such a structure that the backlash amount is reduced by using the pressing means as described above, there has been a problem in that the pressing means is moved in a direction crossing the moving direction in the guide hole by the pressing force (component of force) applied to the worm
106
and abuts on the guide hole to make a sound.
In the electric power steering apparatus disclosed in the Japanese Patent Application Laid-Open No. 2000-43739, moreover, the pressing means provided in the guide hole is fitted in the shaft on one of the ends of the worm and simply abuts on the peripheral surface of the bearing movable in the radial direction. The pressing means does not block the movement of the bearing in a direction crossing the direction of movement of the pressing means. Therefore, when the pressing means presses the worm toward the worm wheel and the steering is assisted in the state in which the rotation center line of the worm is inclined with respect to the rotation center line during non-press, the worm is moved in the radial direction with respect to the rotation center line during the press by the component of force in the radial direction described above so that the worm is eccentrically rotated, in other words, carries out whirling. Consequently, there is also a problem in that the defective engagement of the engagement portion is caused and torque nonuniformity is generated. Moreover, it
Imagaki Susumu
Ito Yoshio
Kinme Shigetaka
Kobayashi Masanori
Oka Kunihiro
Darby & Darby
Koyo Seiko Co. Ltd.
Luby Matthew
Morris Lesley D.
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