Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2001-10-25
2003-11-11
Morris, Lesley D. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C074S3880PS, C074S425000
Reexamination Certificate
active
06644431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric power steering apparatus using a motor as a generating source of steering assistance force and a method of manufacturing a gear used for the electric power steering apparatus.
2. Description of Related Art
An automobile is steered by transmitting rotating operation of a steering wheel disposed at the interior of passenger's room to a steering mechanism disposed at the exterior of the room for turning tire wheels for steering (front wheels, in general).
FIG. 1
is a cross-sectional view showing a constitution of a conventional electric power steering apparatus.
The figure shows an example of an electric power steering apparatus for an automobile, comprising: a first steering shaft
101
connected to a steering wheel
100
for steering; a second steering shaft
103
connected at one end thereof via a torsion bar
102
to said steering shaft
101
coaxially and at the other end thereof to a steering mechanism joined to tire wheels; a torque sensor
104
for detecting a torque applied on the first steering shaft
101
with rotation of the steering wheel
100
based on torsion generated on the torsion bar
102
; a steering assist motor
105
to be driven based on the result of detection of said torque sensor
104
; and a reduction mechanism joined to an output shaft of said motor
105
for reducing rotation of said output shaft and transmitting the reduced rotation to the second steering shaft
103
. Said reduction mechanism has a worm
106
and a worm wheel
107
. The electric power steering apparatus is constituted to lighten driver's load for steering by assisting the action of the steering mechanism corresponding to rotation of the steering wheel
100
with rotation of the motor
105
.
The worm
106
constituting the reduction mechanism is supported at the interior of a housing
108
via a pair of antifriction bearings (not illustrated). The second steering shaft
103
provided with the worm wheel
107
is supported at the interior of the housing
108
via a pair of antifriction bearings
109
,
109
.
The worm wheel
107
comprises a ring-shaped tooth body
110
made of synthetic resin which has teeth meshing with the worm
106
and a support body
111
made of metal engaged with the interior side of said tooth body
110
. The tooth body
110
made of synthetic resin reduces a jarring noise made by meshing with the worm
106
and realizes high workability of the teeth. A plurality of locking grooves
114
(see
FIG. 2
) are provided on a peripheral surface of the support body
111
, and prevents relative rotation of the tooth body
110
and the support body
111
.
FIG. 2
is a cross-sectional view showing a constitution of a conventional support body. The support body
111
of the worm wheel
107
is formed through cut processing as in
FIG. 1
or through cold forging as in FIG.
2
. The support body
111
formed through cold forging comprises: a cylindrical part
112
engaged with the tooth body
110
; a plate part
113
extended inward in a radial direction from one end of said cylindrical part
112
; and the locking grooves
114
provided on the peripheral surface of the cylindrical part
112
. The support body
111
is integrally united with the tooth body
110
by placing the support body
111
in a mold for injection molding and performing injection molding.
However, when the support body is formed through cut processing and cold forging, there arises a problem that unnecessary deposit cannot be removed enough. The support body with great weight enlarges inertial force at the time of steering, and causes a deterioration of feeling of steering. In addition, cut processing and cold forging were disadvantageous in comparison with press forming from the viewpoint of manufacturing costs.
The present applicant has applied an electric power steering apparatus a support body of which is press-formed (Japanese Patent Application Laid-Open No. 2001-206230).
The engagement part of the press-formed support body with the tooth body comprises a disc part having a plurality of through holes to be filled with synthetic resin for molding the tooth body which penetrate in an axial direction and a curved edge part provided with a plurality of locking grooves which is curved in an axial direction from an exterior edge of said disc part.
A remedy has been desired for solving the following problems of the press-formed support body. One problem is that the support body is complicated in structure since a relative slide of the tooth body and the support body is hindered at two positions which are the through holes and the curved edge of the engagement part. Another problem is that circularity of synthetic resin in the mold for injection molding at the time of molding the tooth body is low since the synthetic resin for molding the tooth body is filled into the through holes of the engagement part, which results in generation of voids and weld marks.
In order to simplify a structure of the engagement part of the press-formed support body, a support body without the through holes is conceivable. Such a support body should have a curved edge which is long in an axial direction provided with locking grooves on the peripheral surface thereof to ensure an enough contact area with the tooth body. However, manufacture of said support body requires use of a relatively expensive and large presser to perform plastic deformation exclusively on the locking groove part on the peripheral surface of the support body. Consequently an amortization expense of the presser is added to a unit price of the support body, and the unit price of the support body amounts to approximately the same as that of the support body provided with the through holes.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made to settle the problematic points as described above. One object of the invention is to provide an electric power steering apparatus with which resin can be deposited uniformly, costs can be reduced, and a corrugated cylinder part can be engaged with a tooth body without generating voids and weld marks. Said electric power steering apparatus is constituted with the tooth body made of synthetic resin engaged with the exterior side of the corrugated cylinder part, said corrugated cylinder part being press-formed to deform the support body made of metal engaged with the interior side of said tooth body into a corrugated form corrugating in a peripheral direction.
Another object of the invention is to provide a method of manufacturing a gear with which a corrugated cylinder part with relatively long concavities can be provided simply by forming the relatively long concavities of the corrugated part with a relatively small presser. With said manufacturing method, the corrugated part configured as a corrugated plate is provided by performing press forming on a peripheral side of a metal plate circularly and the corrugated cylinder part is provided by bending said corrugated part into a cylindrical form with respect to a plate part. In the next place, the tooth body made of synthetic resin is integrally molded on the exterior side of said corrugated cylinder part.
The electric power steering apparatus according to the present invention is constituted to assist steering by transmitting rotation of a steering assist motor to a steering mechanism via a driving gear and a driven gear which has a ring-shaped tooth body made of synthetic resin meshing with said driving gear and a support body made of metal engaged with the interior side of said tooth body. The support body of the electric power steering apparatus comprises a corrugated cylinder part press-formed to have a plurality of concavities on the exterior side thereof and convexities to the interior side formed by said concavities which are arranged in a peripheral direction and a plate part an exterior edge of which is united with an end of said corrugated cylinder part.
With this constitution, unnecessary deposit on the support body can be removed satis
Kuze Masashi
Matsubara Hideo
Minami Mitsuharu
Shiina Akihiko
Birch & Stewart Kolasch & Birch, LLP
Koyo Seiko Co. Ltd.
Lum L.
Morris Lesley D.
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