Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2002-06-13
2003-09-23
Black, Thomas G. (Department: 3663)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C180S006240, C180S006600, C180S009380, C180S253000, C180S408000, C180S431000
Reexamination Certificate
active
06625529
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for controlling steering angles of front and rear wheels of a vehicle.
2. Description of the Related Art
As a steering mode of a four-wheeler, a front wheel steering mode of giving steering angles only to front wheels is generally adopted. However, according to a front/rear wheel (four-wheel) steering mode of giving steering angles also to rear wheels, improvements of drivability and stability can be made, which include reduction of the minimum turning radius and stabilization of a cornering attitude at an intermediate high speed.
In the front/rear wheel steering mode, there is a mechanical transmission mode, in which steering systems of front and rear wheels are mechanically coupled to each other, and there is a mode realized in a steering angle control apparatus for front and rear wheels of a vehicle, in which the steering systems of the front and rear wheels are not mechanically coupled to the steering wheel, and adjustment can be made for steering angles of the front and rear wheels independently with respect to a manipulated variable of the steering wheel. In this apparatus, a method is conceived readily, which manipulates the steering wheel so that the steering angles of the front and rear wheels can be changed by an equal amount in a phase reverse to each other in order to reduce the minimum turning radius of the vehicle.
However, in such an apparatus, the vehicle has behaved such that a part thereof is greatly swung outward when the vehicle is parked parallel in a forward motion or when the vehicle is turned.
SUMMARY OF THE INVENTION
In order to solve the foregoing problem, the following method of suppressing a large outward swing of a part of the vehicle is conceived. Specifically, when steering angles of front and rear wheels of the vehicle are adjusted so as to realize target steering angles of the front and rear wheels, a reference steering angle in the case where a manipulated variable of a steering wheel is maintained constant is operated in response to the manipulated variable of the steering wheel, determination is made as to whether steering is in an increase state where a direction of steering wheel manipulation and a direction changed thereby coincide with each other or in a return state where the direction of steering wheel manipulation and a direction changed thereby contradict each other, and when the determination is made that the steering is in the increase state, the reference steering angle is corrected so that an azimuth &thgr; to a rotation center (hereinafter referred to as a “rotation center azimuth”) can be reduced, and is set as the target steering angle, and when the determination is made that the steering is in the return state, the reference steering angle is corrected so that the rotation center azimuth &thgr; can be increased, and is set as the target steering angle.
However, since the direction changed by the manipulated variable of the steering wheel and a traveling direction of the vehicle are different from each other, in some cases, a feeling of wrongness that the traveling direction of the vehicle is difficult to be manipulated is given to a driver, or ride comfort of the driver and a passenger is deteriorated by a large lateral acceleration applied to the vehicle.
For example, such a problem is sometimes caused in parking the vehicle parallel in a forward motion. Now, description will be made for a point of this problem based on simulation results shown in
FIGS. 19A
to
24
.
FIGS. 19A
to
19
E are time charts in the case of carrying out the parallel parking in the forward motion by steering only the front wheels, each chart showing a change as below.
FIG. 19A
is a chart of the manipulated variable of the steering wheel,
FIG. 19B
is a chart of the rotation center azimuth,
FIG. 19C
is a chart of the vehicle traveling direction,
FIG. 19D
is a chart of the variable of the vehicle traveling direction, and
FIG. 19E
is a chart of the change of the lateral acceleration. Here, when the manipulated variable of the steering wheel is a positive value, manipulation to the left direction with respect to the neutral position is shown, and when the manipulated variable is a negative value, manipulation to the right direction with respect to the neutral position is shown. Moreover, as shown in
FIG. 20
, the vehicle traveling direction is set at an angle formed by a traveling direction of a reference point on the vehicle and an axis of abscissas of
FIG. 20
, and a left-hand (counterclockwise) direction is defined as positive. Here, the reference point on the vehicle is set at a bisection point of a segment connecting a bisection point of a front axle and a bisection point of a rear axle, that is, a center of the four wheels. The lateral acceleration is defined as positive when it is applied to the right direction with respect to the front of the vehicle, and is defined as negative when it is applied to the left direction with respect thereto.
FIG. 20
is a view showing an orbit of the vehicle for each second in the simulation of the front wheel steering, which is shown in
FIGS. 19A
to
19
E.
FIG. 21
is a view showing an orbit from time t
1
to time t
2
for each second in the orbit of the vehicle in the simulation of the front wheel steering, which is shown in
FIGS. 19A
to
19
E.
Meanwhile, steering control for correcting the target steering angle is carried out so as to correct the rotation center azimuth &thgr; in response to the steering increase/steering return state, the steering control being carried out with respect to the manipulated variable of the steering wheel, which is equal to the simulation shown in
FIGS. 19A
to
19
E.
FIGS. 22A
to
22
E are diagrams showing the following respective values in this case.
FIG. 22A
is a diagram showing the manipulated variable of the steering wheel, the diagram being the same as the chart of FIG.
19
A.
FIG. 22B
is a diagram showing a rotation center azimuth,
FIG. 22C
is a diagram showing a vehicle traveling direction,
FIG. 22D
is a diagram showing a variable of the vehicle traveling direction, and
FIG. 22E
is a chart showing a change of a lateral acceleration.
FIG. 23
is a diagram showing an orbit of the vehicle in the simulation of the front/rear wheel steering, which is shown in
FIGS. 22A
to
22
E, for each second.
FIG. 24
is a diagram showing an orbit from the time t
1
to the time t
2
for each second in the orbit of the vehicle in the simulation of the front/rear wheel steering, which is shown in
FIGS. 22A
to
22
E.
When a comparison is made between the vehicle traveling direction in the front wheel steering shown in FIG.
19
C and the vehicle traveling direction in the front/rear wheel steering shown in
FIG. 22C
, it is understood that the vehicle traveling directions in the front wheel steering and the front/rear wheel steering are greatly different from each other in sections from the time t
1
to the time t
2
and from time t
3
to time t
4
. Moreover, when a comparison is made between the vehicle orbit in the front wheel steering shown in FIG.
21
and the vehicle orbit of the front/rear wheel steering shown in
FIG. 24
, it is understood that, in the section from the time t
1
to the time t
2
while the manipulated variable of the steering wheel is changed to the right direction, the vehicle travels in the left direction in the front/rear wheel steering, whereas the vehicle travels in an approximately constant direction in the front wheel steering.
Hence, in some cases, the vehicle traveling direction does not coincide with the direction where the manipulated variable of the steering wheel is changed, due to the above-described phenomena, so that the feeling of wrongness that the vehicle traveling direction is difficult to be controlled is given to the driver.
Furthermore, when a comparison is made between
FIG. 19D
showing the variable of the vehicle traveling direction in the front wheel steering and
FIG. 22D
showing the variable of the vehicle trave
Deguchi Yoshitaka
Obata Takeaki
Black Thomas G.
To Tuan C
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