Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1997-09-08
2001-05-29
DePumpo, Daniel G. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S443000
Reexamination Certificate
active
06237713
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, as Japanese Patent Application Laid-Open No. 8-98451, is known.
Such 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 (which hereinafter may simply be referred to as “the 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
by way of a ball screw mechanism
53
arranged at the left end of the armature shaft
56
in FIG.
5
. Note that the armature shaft
56
is supported at a right side portion thereof by an angular bearing
65
held within housing
61
.
The ball screw mechanism
53
has a well known constitution, which comprises a large number of balls
64
arranged between a nut section
62
and a screw section
63
thereof, the nut section
62
being press-fit into and caulked against the armature shaft
56
. With this arrangement, the rotary power of the electric motor
53
is transmitted to the rack-shaft
51
by way of the nut section
62
, the balls
64
and the screw section
63
to produce axial reciprocative power there, which is then used to assist the steering power.
A power steering unit having the above described configuration is then mounted onto the vehicle by securely fitting the housing
61
on the right side of
FIG. 5
to the vehicle main body and fitting the yoke
55
on the left side of
FIG. 5
by a bracket
70
as in the case of a hydraulic power steering unit. More specifically, the housing
61
is directly fitted to the vehicle by securing a fitting section
69
that is an integral part of the housing
61
to the vehicle main body by means of screws. On the other hand, the yoke
55
is fitted to the vehicle by holding the end of a pipe-shaped diameterically small portion
55
a
(on the left side in
FIG. 5
) of the yoke
55
under the bracket
70
having a U-shaped cross section at a middle portion thereof. Note that an elastic member (not shown) typically made of rubber is arranged around the diametrically small portion
55
a
of the yoke
55
so that the yoke
55
is held under the U-shaped area of the bracket
70
with the elastic member disposed therebetween. The strength with which the unit is secured largely depends on the strength of securing the housing
61
because the housing
61
is by far securer than the bracket
70
when fitted to the vehicle main body.
A hydraulic power steering unit typically comprises a combination of pipe-shaped member and a housing, the housing being located close to the steering column. Since, unlike the housing, it is not possible to provide the pipe-shaped member with a fitting section, the member has to be secured in position by means of a bracket. If, on the other hand, the housing is secured by means of a bracket, the pipe-shaped member is required to show an enhanced strength when fitted in position and a further housing has to be located at the side of the pipe-shaped member for the sake of the strength. Thus, with a hydraulic power steering unit, it is the most common practice to rigidly secure the housing to the vehicle main body and hold the pipe-shaped member in position by means of a bracket because this technique is advantageous particularly in terms of cost and this practice is normally followed by electric power steering units.
As described above, with a conventional power steering unit, a component thereof located close to the steering column
54
of the motor vehicle, that is, the housing
61
is rigidly and directly secured to the vehicle main body. However, while such a constitution shows a greater holding strength than when it is secured by means of a bracket, it is then less apt to damp the sounds and vibrations transmitted to it from the vehicle main body. Therefore, a power steering unit shown in
FIG. 5
is accompanied by a problem that it cannot damp the controlling sounds and vibrations of the electric motor
52
and hence they may be easily transmitted to the steering column
54
. It would be appreciated that, while the noises generated outside the motor vehicle are apt to be drowned by the sounds of the moving vehicle and its engine so that they may provide less nuisance to the passengers in the vehicle, the sounds and vibrations transmitted to the steering column
54
can then be conveyed to the inside of the vehicle by way of the steering wheel. Therefore, the sounds are confined in the room of the vehicle and they give nuisances to the driver and passengers in the vehicle and possibly interfere with the steering feeling of the driver.
Additionally, since a conventional housing
61
as shown in
FIG. 5
has a fitting section
69
projecting in a direction that is three-dimensionally different from the projecting direction of the member that holds the steering column
54
so that a costly mold having a complicated cavity profile has to be used for manufacturing the housing to push up the manufacturing cost.
Still additionally, motor vehicles of different types have different positions for securing the power steering unit to the vehicle main body. Therefore, since the fitting section
69
of the housing
61
is fixed, different housings in which the position of the fitting section
69
is different from each other should be prepared for motor vehicles of different types corresponding to the securing position. This means that different types of motor vehicle require different complicated molds and many kinds of products is required for each types. Accordingly, the management of the products is very troublesome and it raises the manufacturing cost of the unit.
An object of the present invention is to provide an electric power steering unit that can effectively prevent the sounds and vibrations of its electric motor from being transmitted to the steering wheel.
Another object of the present invention is to provide an electric power steering unit which can simplify the cavity profile of the molds and allow the housing of the steering column side to be commonly used in motor vehicles of different types.
The above-described and other objects, and novel feature of the present invention will become apparent more fully from the description of the following specification in con
Kodaira Tadao
Onodera Tsugio
Taniguchi Yoshiaki
DePumpo Daniel G.
McCormick Paulding & Huber LLP
Mitsuba Corporation
LandOfFree
Electric power steering unit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric power steering unit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric power steering unit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2440387