Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2001-12-31
2003-12-09
Morris, Lesley D. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
Reexamination Certificate
active
06659219
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric power steering device for motor vehicles.
2. Prior Art
The electric power steering device for motor vehicles is equipped with a mechanism which transmits the rotation of a steering shaft rotated by the operation of a steering wheel, to a rack shaft through a pinion, thereby steering vehicle driving wheels through a tie rod connected to either end of the rack shaft. Furthermore an auxiliary motor for steering device is equipped. With the detection of a steering torque produced at the steering shaft, the motor is excited in accordance with a signal of the detection. The driving torque of the motor is transmitted to a steering rack shaft, to thereby assist the steering force of the steering wheel.
For the electric power steering device of the above constitution, there have been proposed various kinds of configurations as seen in Japanese Laid Open Patent Publication No. H7-165089, Japanese Laid Open Patent Publication No. H8-301130, Japanese Laid Open Patent Publication No. H10-95354, and Japanese Laid Open Patent Publication No. 2000-168581. One example of configurations of such prior art electric power steering devices will be explained by referring to FIG.
3
.
FIG. 3
is a sectional view that shows a major portion of the configuration of the steering rack shaft and motor section of the electric power steering device. In
FIG. 3
, numeral
101
denotes a steering rack shaft; and
102
represents a steering shaft. The steering shaft
102
is fitted with an unillustrated pinion, which meshes with the teeth of the rack on the rack shaft
101
.
In
FIG. 3
, a screw
107
b
of a later-described ball nut mechanism is formed on the left side of the rack shaft
101
. Further the left end of the rack shaft
101
is connected with a tie rod not shown.
Numerals
103
and
104
denote housings. A first housing
103
and a second housing
104
are so constituted as to be separably connected at the part A. In the first housing
103
is mounted a later-described motor for assisting the steering force. In the second housing
104
a later-described ball nut mechanism
107
is arranged. The rack shaft
101
is penetrated through the inside of the first housing
103
and the second housing
104
, and axially slidably supported.
Numeral
105
represents a motor mounted coaxially with the rack shaft
101
to assist the steering force. A stator
105
a
is fixedly mounted in the first housing
103
, while a rotor
105
b
is coaxially mounted outside of the rack shaft
101
and is rotatably supported by bearings
106
a
and
106
b
inside of the first housing
103
.
Numeral
107
denotes a ball nut mechanism, which includes a hollow cylindrical nut
107
a
provided with an internal groove of an approximately semicircular form in cross section on the inner surface, a screw
107
b
with an external groove of an approximately semicircular form in cross section on the outer surface of the rack shaft
101
, and a number of balls
107
c
recirculating, while rolling, in the spiral groove formed by the inner and external grooves.
The nut
107
a
of the ball nut mechanism
107
is rotatably supported by on a bearing
108
mounted inside of the second housing
104
.
In
FIG. 3
, inside the right end portion of the nut
107
a
are formed internal spline grooves
107
s,
which mesh with spline teeth
105
s
formed on the left end portion of the rotor
105
b
of the motor
105
as shown in FIG.
3
. The nut
107
a
and the rotor
105
b
are connected as one body in the direction of rotation and slidably splined in the axial direction.
The rack shaft
101
is axially slidably supported at only two positions: at an unillustrated guide which is located in a section where a pinion provided on a steering shaft
102
meshes with the rack teeth formed on the rack shaft
101
, and at the ball nut mechanism
107
.
When, in the above-described constitution, the electric current determined in accordance with the steering torque is supplied to the motor
105
, the rotor
105
b
turns to thereby turn the nut
107
a
of the ball nut mechanism
107
which is splined with the rotor
105
b.
The rotation of the nut
107
a
axially moves the rack shaft
101
, thus operates the steering mechanism through the tie rod.
The above-described prior-art electric power steering device is assembled by the following procedure. That is, first the stator
105
a
of the motor
105
is secured in the first housing
103
, and then the bearings
106
a
and
106
b
are set in the first housing
103
, to thereby rotatably support the rotor
105
b
of the motor
105
.
Furthermore, the bearing
108
is set in the second housing
104
, to thereby rotatably support the nut
107
a
of the ball nut mechanism
107
.
Next, the first housing
103
and the second housing
104
are jointed at the portion A. At this time, the nut
107
a
and the rotor
105
b
are adjusted in position so as to be in the same phase in the direction of rotation so that the inner spline grooves
107
s
formed in the right end portion of the nut
107
a
shown in FIG.
3
and the spline teeth
105
s
formed on the left end portion of the rotor
105
b
shown in
FIG. 3
will mutually mesh, and that the nut
107
a
and the rotor
105
b
will be splined simultaneously with the connection of the housing section.
According to the prior-art constitution, the two component members, that is, the outer housing section and the members arranged in the housing, are simultaneously connected. Besides, at the time of this connection, these two members arranged in the housing need phase adjustment in the direction of rotation and then are connected. This procedure is complicated and hard to perform, and therefore will be of low working efficiency. This invention, therefore, is intended to cope with the above-described disadvantage.
SUMMARY OF THE INVENTION
1. A primary object of this invention is to provide a new electric power steering device capable of easily mounting and assembling, a power transmission device including a plurality of members which transmit the rotation of the motor for assisting the steering force, to the steering shaft through a ball nut mechanism.
2. Another object of this invention is to provide a new and easy-to-assemble electric power steering device of the following construction. The housing is separated into a first chamber and a second chamber. In the first chamber, the motor for assisting the steering force is inserted from one end of the housing. In the second chamber, a rack shaft assembly including a rack shaft to be connected to the steering shaft and a ball screw mechanism is inserted from the other end of the housing. The rotor of the motor for assisting the steering force and the rack shaft are connected through the ball screw mechanism so that the rack shaft will pass through the first and second chambers.
3. Further another object of this invention will be clearer from the detailed description of the preferred embodiments with reference to the accompanying drawings.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.
REFERENCES:
patent: 4577715 (1986-03-01), Saito
patent: 6178839 (2001-01-01), Yoshida et al.
patent: 6454042 (2002-09-01), Yoshida et al.
patent: 07-165089 (1995-06-01), None
patent: 08-301130 (1996-11-01), None
patent: 10-095354 (1998-04-01), None
patent: 170866 (2000-06-01), None
patent: 2000-168581 (2000-06-01), None
patent: 318629 (2000-11-01), None
patent: 145080 (2002-05-01), None
patent: 002220 (2003-01-01), None
Eda Hiroshi
Fukuda Toshihiro
Okada Jun
Luby Matthew
Morris Lesley D.
NSK Ltd.
Sidley Austin Brown & Wood LLP
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