Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
2001-11-29
2003-07-01
Hurley, Kevin (Department: 3618)
Motor vehicles
Steering gear
With fluid power assist
C180S444000, C180S448000, C074S422000, C074S498000
Reexamination Certificate
active
06585074
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vehicle steering system capable of controlling the steered angle or the steerable wheels independently of steering operation of the driver.
BACKGROUND OP THE INVENTION
While the vehicle is running, there occurs frequent changes in external factors such as road surface conditions, wind direction and so, which may change the vehicle running and steering conditions abruptly. The driver continues to manipulate the steering wheel in an appropriate manner so as to maintain a stable running condition. For instance, when the vehicle is running at high speeds, lateral wind force acting on one side of the vehicle may obstruct smooth straight ahead running of the vehicle. The driver should endeavor to keep the vehicle running straight ahead against the lateral wind (external factor), which is tiresome.
In view of this, various attempts have been made in recent years to develop a steering system, which is capable of assisting the driver's vehicle maneuvering operation according to underlying vehicle running and steering conditions, thereby improving the control stability and maneuverability or the vehicle. One example of such improved steering systems is disclosed in Japanese Patent No. 2501606.
The disclosed steering system
300
, as shown here in
FIG. 11
, includes a gear housing
303
connected via left and right links
302
,
302
to a vehicle body
301
such that the gear housing
303
is displaceable in the widthwise direction of the vehicle body
301
. The gear housing
303
is also supported by left and right elastic members
304
,
304
on the vehicle body
301
such that the gear housing
303
is displaceable both in the radial direction and the widthwise direction thereof. The steering system
300
has an actuator
306
mounted to the vehicle body
301
via an elastic member
305
. The actuator
308
has an actuating rod
307
connected to one end of an L-shaped arm
308
, the other end of the arm being firmly connected to the gear housing
303
.
The gear housing
303
contains within it a rack and pinion mechanism
311
. The rack and pinion mechanism
311
has a pinion
315
connected to a steering wheel
312
via a steering shaft
313
and a set of shaft couplings
314
,
314
, and a rack
318
connected to steerable wheels (front wheels)
316
,
316
via tie rods
317
,
317
.
With this arrangement, when the driver turns the steering wheel
312
in one direction, the steering system
300
operates to swivel the steerable wheels
316
,
316
in the same direction via the rack and pinion mechanism
311
. The same swivel motion of the steerable wheels
316
,
316
can also occur when the actuator
306
operates to extend or contract its actuating rod
307
to move the gear housing
303
in a widthwise direction of the vehicle, thereby displacing the rack and pinion mechanism
311
as a whole in the same widthwise direction of the vehicle.
Here, the total amount of axial displacement (S
30
) of the rack
318
is represented by a combination or the amount of axial displacement (S
31
) of the rack
318
achieved by manual steering operation of the driver at the steering wheel
312
and the amount of axial displacement (S
32
) of the rack
318
achieved by operation of the actuator
306
(S
30
=S
31
±S
32
). This means that the actuator
306
can assist the manual steering operation. The actuator
306
can control the range of the steering ratio, which is represented by the ratio of the steering angle of the steering wheel
312
to the steered angle of the steerable wheels
316
. The steering ratio is also called “steering angle ratio”.
The maximum controlled variable achieved by the actuator
306
, that is, the amount of maximum axial displacement (
332
) of the rack
318
achieved by the actuator
306
, is determined depending on the stroke of the actuating rod
307
and the maximum range of displacement of the gear housing
303
. Thus, the amount of axial displacement (S
32
) of the rack
308
achieved by the actuator
306
is limited to a certain range.
The rack and pinion mechanism
311
of the conventional steering system
300
has a fixed gear ratio (the number of full turns of the pinion
315
required to move the rack
318
all the way from left to right).
Due to the fixed gear ratio of the rack and pinion mechanism
311
, the rack gain of the conventional steering system
300
is always constant regardless or the steering angle, as shown in FIG.
12
A. The rack gain is represented by the amount of axial displacement (mm) of the rack achieved when the pinion (that is, the steering wheel) makes a single complete turn. The rack gain is also called “relative stroke”. In the table shown in
FIG. 12A
, the y-axis represents the rack gain (mm/turn) and the x-axis the steering angle (degrees) of the steering wheel
312
. The midpoint on the x-axis represents the neutral position of the steering wheel, at which the steering angle of the steering wheel is 0 degree. In each rotational sense, the steering system
300
has the same range of steering angles.
FIG. 12B
is a graph showing a steering ratio characteristic curve St
1
of the conventional steering system
300
. The y-axis of the graph is the Steering ratio (deg/deg) and the x-Axis of the graph is the steering angle (deg) of the steering wheel. The smaller the steering ratio, the larger the steered angle of the steerable wheels in relation to the steering angle of the steering wheel. The steering ratio characteristic represented by the curve St
1
depends solely on the amount of axial displacement of the rack achieved by manual steering operation of the driver in the absence of the assistance by the actuator.
Because of the constant or fixed rack gain shown in
FIG. 12A
, the steering ratio characteristic curve St
1
shown in
FIG. 12B
indicates that the steering ratio is maximum when the steering wheel is in the neutral position, and it becomes small as the steering angle increases. When the steering wheel is in the neutral position, the steering ratio is R
2
. When the steering wheel is in its left or right end position of A maximum steering angle &thgr;
12
, the steering ratio is R
1
, which is smaller than R
2
(R
1
<R
2
).
Thus, a large (or high) steering ratio achieved in relation to a relatively small steering angle responds more slowly to the steering wheel, so that the steerable wheels are steered slowly. Conversely, a small (or low) steering ratio achieved in relation to a relatively large steering angle respond more quickly to the steering wheel, so that the steerable wheels are steered relatively quickly. This is due to a reason, which will be discussed below with reference to
FIGS. 13A-13B
and
14
.
FIG. 13A
is a diagrammatical plan view of a generally used vehicle steering system, and
FIG. 13B
is a diagrammatical side view of a steerable wheel of the steering system. In
FIG. 13B
, reference character Fr and Rr represent the forward direction and the backward direction, respectively, as viewed from the driver. As shown in
FIG. 13A
, the steering system
400
includes a rack and pinion mechanism
401
having a rack
402
connected at one end to one end or a tie rod
404
via a first universal joint
403
, a knuckle arm
406
connected at one end to the other end of the tie rod
404
via a second universal joint
405
, a kingpin
408
connected to the other end of the knuckle arm
404
, and a steerable wheel
407
mounted to swivel or turn about the axis of the kingpin
408
.
When a steering wheel
409
is manipulated or turned in one direction by the driver, manual steering force is transmitted successively through a pinion
401
a
and a rack gear
401
of the rack and pinion mechanism
401
, the rack
402
, the tie rod
404
and the knuckle arm
406
to the steerable wheel
407
so that the steerable wheel
407
is turned in the same direction as the steering wheel.
The steered angle of the steerable wheel
407
is a rotational angle about the axis of the kingpin
408
when viewed in the plan view. The three-dimensional leng
Akuta Yoshimitsu
Katou Takafumi
Matsuura Kazuo
Takikawa Keiichi
Honda Giken Kogyo Kabushiki Kaisha
Hurley Kevin
Luby Matthew
Merchant & Gould P.C.
LandOfFree
Vehicle steering system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Vehicle steering system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vehicle steering system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3018516