Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1999-01-18
2001-02-13
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering gear
With electric power assist
C074S459500, C074S3880PS
Reexamination Certificate
active
06186268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric power steering unit to be used for a vehicle and, more particularly, it relates to a field of technology effectively applicable to electric power steering gears to be used for rack and pinion type steering systems.
2. Related Art Statement
In recent years, most vehicles are equipped with a so-called power steering gear, and various type power steering unit, such as a hydraulically or electrically operated type power steering unit has been designed to assist the steering power of the vehicle. In these electric power steering units, as one for applicable to rack and pinion type steering systems, a unit which the steering assisting power is obtained by an electric motor arranged coaxially with a rack-shaft is known.
FIG. 5
is a cross-sectional view showing the structure of a conventional electric power steering unit, and
FIG. 6
is an enlarged view showing the main part of the unit shown in FIG.
5
.
An electric power steering unit shown in
FIG. 5
, comprises an electric motor
52
arranged coaxially with a rack-shaft
51
so that the steering assisting power generated by the electric motor
52
is transmitted to the rack-shaft
51
by way of a ball screw mechanism
53
. Then, the guiding wheels of the vehicle can be turned by utilizing both the manual steering power of the driver and the steering assisting power.
The rack-shaft
51
is linked to the guiding wheels typically by way of tie rods or knuckle arms arranged at the respective opposite ends thereof and also linked to the steering column
54
that is coupled to the steering wheel (which hereinafter may be referred to as “the handle”) by way of a rack and pinion gear so that it may be reciprocatively moved in the horizontal directions of
FIG. 5
as the steering operation by the driver. The electric motor
52
has a cylindrical yoke
55
containing coaxially therein a cylindrical armature shaft
56
and a field device
57
and is fed with power from a power supply section
58
. The field device
57
comprises magnets
59
arranged on the inner peripheral portion of the yoke
55
and an armature core
60
arranged on the outer peripheral portion of the armature shaft
56
. The rotary power generated by the electric motor
52
is transmitted to the rack-shaft
51
and the power is converted into the reciprocatively movement by way of a ball screw mechanism
53
arranged at the left end of the armature shaft
56
in
FIG. 5
, so that steering power is assisted.
Meanwhile, in the power steering device shown in
FIG. 5
, the ball screw mechanism
53
comprises a nut section
62
and a screw section
63
, and the nut
62
and the screw
63
are coupled without backlash by balls
64
. The nut
62
of the ball screw mechanism
53
is supported to be rotatable in the housing
61
by an angular bearing
65
.
In this case, a spacer
71
for arranging the angular bearing
65
and the nut
62
to be coaxial with each other is provided therebetween as shown in FIG.
6
. The inner ring side of the angular bearing
65
is fixed by an inner ring fixing ring
74
screwed on an outer circumferential portion of the spacer
71
and by the flange
75
of the spacer
71
, and the outer ring side of the angular bearing
65
is fixed by an outer ring fixing ring
72
screwed on an inner circumferential portion of the housing
61
and by a stepped section
73
of the housing
61
. Meanwhile, the nut
62
is contained inside the spacer
71
, and the nut
62
is fixed by a nut fixing ring
76
screwed on an inner circumferential portion of the spacer
71
. Further, in this manner, the nut
62
is rotatably supported and fixed in the housing
61
through the spacer
71
by the angular bearing
65
.
However, since the angular bearing
65
and the nut
62
are separated from each other in a conventional power steering unit, the spacer
71
as described above is required in order to arrange the bearing
65
and the nut
62
to be coaxial with each other. Therefore, there is a problem that the number of components is increased to raise the costs of products. Hence, there recently was a proposal for an unit in which the nut
62
and the inner ring of the angular bearing
65
are integrated with each other, like the electric power steering unit according to Japanese Patent Application Laid Open No. 9-104351. In this application, the ball screw nut is supported in the housing without using the spacer
71
to reduce the number of components and the size of the product.
Meanwhile, as shown in
FIG. 7
, there is another conventional power steering unit in which one end side of a ball screw nut
81
is received by a thrust bearing
82
and the other end side thereof is supported by an angular bearing
83
. In this case, a pre-load pressure is applied in the axial direction to a pressure member
89
and a fixing screw ring
90
, and the nut
81
is contained and maintained in a lower housing
88
under the pre-load pressure. In addition, a circulation passage
84
is formed inside the nut
81
, and balls
85
move in the passage
84
thereby smoothly converting rotation of the nut
81
into movement in the lateral direction of a rack shaft
87
.
However, since this power steering unit is arranged such that a pre-load pressure is applied to the angular bearing
82
when the nut
81
is fixed into the housing, there is a problem that this pressure is transmitted to balls
85
through the nut
81
and a stress is caused at the balls
85
against the pressure thereby deforming the balls
85
. There also is a problem that a force from the angular bearing
82
is applied to the passage
84
for circulating the balls
85
, so that the passage
84
is deformed and the rolling of the balls
85
is disturbed.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an electric power steering unit arranged such that the support structure of the ball screw mechanism is simplified and a force is not applied to the balls or a circulation passage when fixing its nut.
According to the invention, there is provided an electric power steering unit comprising a rack-shaft to be coupled to the guiding wheels of a vehicle, an electric motor coaxially arranged around the rack-shaft to supply assisting power to the rack-shaft, a ball screw mechanism for connecting a nut section linked to the armature shaft of the electric motor with a screw section formed on the rack-shaft by disposing ball members therebetween and for transmitting the rotary power of the electric motor to the rack-shaft as assisting power for steering, and a housing comprising a bearing for rotatably supporting the ball screw mechanism. The bearing comprising an outer ring pressed and fixed in an axial direction in the housing by a pre-load pressure member, and a rolling member which is provided between the outer ring and the nut section of the ball screw mechanism and which is in contact with the nut section at a position where a stress is not caused at a ball member of the ball screw mechanism by a pressure force applied to the outer ring.
Preferably, the outer ring comprises two ring members separated from each other in an axial direction, and the rolling member is provided between the ring members and both corner portions opposed to the ring members of the nut section.
Still preferably, the outer ring comprises two ring members separated from each other in an axial direction, the nut section has a flange section projecting in a radial direction, and the rolling member is provided between a side surface portion of the flange section and the two ring members.
Also, according to the invention, there is provided an electric power steering unit comprising a rack-shaft to be coupled to the guiding wheels of a vehicle, an electric motor coaxially arranged around the rack-shaft to supply assisting power to the rack-shaft, a ball screw mechanism for connecting a nut section linked to the armature shaft of the electric motor with a screw section formed on the rack-shaft by disposing ball members therebetween and
Onodera Tsugio
Taniguchi Yoshiaki
Johnson Brian L.
Lerner Avraham H.
McCormick Paulding & Huber LLP
Mitsuba Corporation
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