Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2002-11-22
2004-07-20
Morris, Lesley D. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S443000, C701S041000, C701S042000
Reexamination Certificate
active
06763908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a steering device for a vehicle, and more particularly, to a steering device having a sub-steering mechanism that is required upon conducting automatic steering for compensating a steering amount of a steering wheel performed by a driver, or required for steering upon the automatic driving, for example.
2. Description of the Related Art
Control methods relating to steering of vehicles have been proposed in which, for example, auxiliary automatic control of the direction of wheels is performed so as to optimize steering characteristics, i.e., change in an actual traveling direction of a vehicle with respect to the amount of turning of a steering wheel, or an automatic control operates instead of operation by a driver to drive and control a steering system so that a running position of a vehicle is within a predetermined lane.
The applicant of the present invention filed an application for a patent for a steering device for a vehicle such as shown in
FIG. 11
(Japanese Patent Application No. 2001-353130) to perform this kind of wheel steering angle control for a vehicle.
The conventional steering device for a vehicle will be described with reference to
FIG. 11
showing a construction of the device.
In
FIG. 11
, a steering wheel operated by a driver is indicated by reference numeral
1
and a first planetary gear mechanism is indicated by reference numeral
2
. The first planetary gear mechanism
2
is constituted by a sun gear
201
connected to the steering wheel
1
, planetary gears
202
a
and
202
b
supported by a carrier
203
, a ring gear
204
, and a worm wheel
205
for rotating the ring gear
204
.
A second planetary gear mechanism indicated by reference numeral
3
in
FIG. 11
is also provided. The second planetary gear mechanism
3
is constituted by a sun gear
301
, planetary gears
302
a
and
302
b
supported on a carrier
303
, and a fixed ring gear
304
. A shaft indicated by reference numeral
4
connects the carrier
203
of the first planetary gear mechanism
2
and the carrier
303
of the second planetary gear mechanism
3
to each other. The first planetary gear mechanism
2
or the combination of the first planetary gear mechanism
2
and the second planetary gear mechanism
3
is a sub-steering mechanism capable of mechanically adding an auxiliary steering angle to a turning angle of the steering wheel
1
.
A rack-and-pinion steering mechanism indicated by reference numeral
5
in
FIG. 11
is also provided. The rack-and-pinion steering mechanism
5
is constituted by a rack-and-pinion
501
, and a worm wheel
502
capable of reversing the rotation direction and that is used to rotate the pinion
501
with an electric motor
901
used as a wheel steering angle control actuator. Knuckle arms are indicated by reference symbols
6
a
and
6
b
, and wheels to be turned for steering are indicated by
7
a
and
7
b.
A reaction control mechanism indicated by reference numeral
8
in
FIG. 11
is a mechanism for giving the steering wheel
1
a reaction torque by applying a drive torque to the first planetary gear mechanism
2
operating as the sub-steering mechanism. The reaction control mechanism
8
is constituted by a reaction motor
801
for applying the drive torque to the first planetary gear mechanism
2
, and a worm gear
802
which meshes with the worm wheel
205
of the first planetary gear mechanism
2
. The worm gear
802
cannot be rotated by the rotation of the worm wheel
205
. That is, the reaction mechanism can be self-locked.
A wheel steering angle control mechanism indicated by reference numeral
9
in
FIG. 11
is a mechanism for driving the steering mechanism
5
. The wheel steering angle control mechanism
9
is constituted by an electric motor
901
and a worm gear
902
which meshes with the worm wheel
502
of the steering mechanism
5
. The combination of the worm wheel
502
and the worm gear
902
is such that the worm gear
902
can be rotated from the worm wheel
502
side, that is, it can be reversely rotated.
A reaction torque detection means for detecting the reaction torque produced at the steering wheel
1
is indicated by reference numeral
10
in
FIG. 11. A
wheel steering angle detection means
11
for detecting the wheel steering angle of the wheels turned for steering
7
a
and
7
b
and a steering wheel steering angle detection means
12
for detecting the steering angle of the steering wheel
1
are also provided.
A target wheel steering angle production means is indicated by reference numeral
13
in FIG.
11
. The target wheel steering angle production means
13
produces a target wheel steering angle
1301
by computing a necessary wheel steering angle, for example, from an output
1201
from the steering wheel steering angle detection means
12
, a steering request
20
from another system (e.g., a lane keeping device), and a vehicle state signal
21
(e.g., a vehicle speed signal, a yaw rate signal, or the like).
A wheel steering angle control means is indicated by reference numeral
14
in FIG.
11
. The wheel steering angle control means
14
controls the wheel steering angle of the wheels turned for steering
7
a
and
7
b
by driving the wheel steering angle control electric motor
901
so that the target wheel steering angle
1301
and an output
1101
from the wheel steering angle detection means
11
are equal to each other.
A target reaction production means for setting a target value of the reaction torque received by the driver through the steering wheel
1
is indicated by reference numeral
15
in FIG.
11
. The target reaction production means
15
computes a suitable reaction, for example, from the output
1201
from the steering wheel steering angle detection means
12
and the vehicle state signal
21
(e.g., a vehicle speed signal, a yaw rate signal, or the like) to produce a target reaction torque
1501
.
Further, a reaction torque control means is indicated by reference numeral
16
in FIG.
11
. The reaction torque control means
16
controls the reaction torque produced in the steering wheel
1
by driving the reaction electric motor
801
so that the target reaction torque
1501
and an output
1001
from the reaction torque detection means
10
are equal to each other.
As described above, the conventional device controls the wheel steering angle by computing a suitable wheel steering angle, for example, from the operation of the steering wheel
1
performed by the driver and a signal from another system, and simultaneously controls production of the steering wheel reaction in the steering wheel
1
by computing a suitable steering reaction.
However, if the wheel steering angle and the steering wheel reaction are independently controlled in the device having the above-described sub-steering mechanism, as shown in
FIG. 2
, a drive torque is required for the wheel steering angle control electric motor
9
. That is, according to the balance about the wheel steering angle control electric motor (wheel steering angle control mechanism)
9
, a drive torque (Ta+Tb) for a self-alignment torque (road surface reaction) Ta produced in the wheels turned for steering and a torque Tb distributed from the reaction electric motor
8
by the sub-steering mechanisms (planetary gear mechanisms)
2
and
3
is required of the wheel steering angle control electric motor
9
.
On the other hand, according to the balance about the reaction electric motor (reaction control mechanism)
8
, a drive torque (Tb+Tc) for a reaction torque Tc produced in the steering wheel
1
and Tb distributed by the sub-steering mechanisms
2
and
3
, is required for the reaction electric motor
8
.
Thus, the steering system using the above-described steering device has a problem in that it consumes a larger amount of energy in comparison with the ordinary power steering system. For ease of description, the gear ratios of the planetary gear mechanisms
2
and
3
, the gear ratio of the steering mechanism
5
, and so on have been shown
Ogawa Kenji
Shirasawa Kazushi
Lum L.
Mitsubishi Denki & Kabushiki Kaisha
Morris Lesley D.
Sughrue & Mion, PLLC
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