Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-01-16
2002-09-10
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S001000, C701S072000, C180S006200, C180S006600, C180S006440
Reexamination Certificate
active
06449543
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a steering device for vehicle, which utilizes a so-called steer by electric wire system.
DESCRIPTION OF THE RELATED ART
In a vehicle steering device that employs a steer by electric wire system, the movement of a steering actuator, which corresponds to the operation of an operating member modeled on a steering wheel, is transmitted to the wheels of the vehicle in such a manner that the steering angle changes without this operating member being coupled mechanically to the wheels. In a vehicle that employs a steer by electric wire system such as this, a proposal has been made for computing a target yaw rate corresponding to the amount of operation of the operating member, and controlling the steering actuator such that the target yaw rate coincides with the actual yaw rate so as to stabilize the behavior of the vehicle.
FIG. 13
shows an example of a control block diagram of a vehicle steering device employing a conventional steer by electric wire system.
In the control block diagram, K
1
is the gain of a target yaw rate &ggr;* relative to the operating angle &dgr;h of an operating member
101
, and a steering device computes a target yaw rate &ggr;* from the stored relationship of &ggr;*=K
1
·&dgr;h, and an operating angle &dgr;h detected by a sensor. K
2
is the gain of a target steering angle &dgr;* relative to the deviation between the target yaw rate &ggr;* and the actual yaw rate &ggr; of a vehicle
100
, and a steering device computes a target steering angle &dgr;* from the stored relationship of &dgr;*=K
2
·(&ggr;*−&ggr;), the computed target yaw rate &ggr;*, and a yaw rate &ggr; detected by a sensor. The gain K
2
is regarded as a function of velocity V, and is set such that it decreases in line with an increase in velocity V in order to ensure stability at high speeds. Ga is the transfer function of the target drive current Ia* of the steering actuator
102
relative to the deviation between a target steering angle &dgr;* and the actual steering angle &dgr; of the vehicle, and the steering device computes a target drive current Ia* from the stored relationship of Ia*=Ga·(&dgr;*−&dgr;), the computed target steering angle &dgr;*, and a steering angle &dgr; detected by a sensor. The transfer function Ga is set, for example, such that proportional integral (PI) control is performed. K
3
is the gain of a target operating torque Th* relative to the operating angle &dgr;h of operating member
101
, and the steering device computes a target operating torque Th* from the stored relationship of Th*=K
3
·&dgr;h and an operating angle &dgr;h detected by a sensor. Gb is the transfer function of the target drive current Ib* of the operating actuator
103
relative to the deviation between the target operating torque Th* and the actual operating torque Th, and the steering device computes a target drive current Ib* from the stored relationship Ib*=Gb·(Th*−Th), the computed target operating torque Th* and an operating torque Th detected by a sensor. The transfer function Gb is set, for example, such that proportional integral (PI) control is performed.
In the above-mentioned conventional constitution, because the actual yaw rate &ggr; of a vehicle does not increase when the coefficient of friction between the surface of a road and the tires is reduced by surface icing, or when tire lateral force reaches its limit, a saturated state results in which the yaw rate &ggr; does not attain the target yaw rate &ggr;* when operating torque Th increases, and there is a possibility of the steering angle &dgr; diverging, and of vehicle behavior becoming unstable.
That is,
FIG. 14
(
1
) and
FIG. 14
(
2
) is one example of simulation results in a steering device constituting the above-mentioned conventional steer by electric wire system, showing changes over time in the yaw rate &ggr;, target yaw rate &ggr;* and steering angle &dgr; relative to a step input of 2.7 N·m operating torque Th at times t
1
to t
2
(0.5 to 5 seconds), in a vehicle travelling at a velocity of 60 km/hour, wherein the coefficient of friction between the vehicle and the surface of the road is regarded as 1 up until t
3
(2.5 seconds), and is regarded as 0.1 thereafter. The fact that the deviation between the yaw rate &ggr; and the target yaw rate &ggr;* increases, and the steering angle &dgr; diverges in accordance with the drop in the coefficient of friction is shown.
Further,
FIG. 15
(
1
) and
FIG. 15
(
2
) depict Bode diagrams showing an example of yaw rate &ggr; frequency response simulation relative to operating torque input in a steering device constituting the above-mentioned conventional steer by electric wire system, wherein a vehicle is travelling at a velocity of 20 km/hour. Further,
FIG. 15
(
3
) and
FIG. 15
(
4
) depict Bode diagrams showing an example of yaw rate &ggr; frequency response simulation relative to operating torque input in a conventional steering device in which a steering wheel is mechanically coupled to the vehicle wheels, wherein a vehicle is travelling at a velocity of 20 km/hour.
FIG. 15
(
1
) through
FIG. 15
(
4
) indicate that, at low travelling velocity, yaw rate responsiveness relative to operating torque input decreases more in a vehicle steering device employing a conventional steer by electric wire system than in a steering device in which a steering wheel is mechanically coupled to the vehicle wheels.
An object of the present invention is to provide a vehicle steering device capable of solving the above-mentioned problem.
SUMMARY OF THE INVENTION
A steering device for vehicle of the present invention comprises an operating member operated by being rotated; a steering actuator driven in accordance with the operation of the operating member; means for transmitting the movement of the steering actuator to wheels of the vehicle such that the steering angle changes in accordance with the movement without mechanically coupling the operating member to the wheels; an operating actuator for generating control torque, which acts on the operating member; means for determining a load torque, which is sum of the control torque and the operating torque exerted on the operating member by a driver; means for determining the operating angle of the operating member which is operated by the action of the load torque; means for computing a target behavior index value of the vehicle, comprising at least a target yaw rate corresponding to the determined load torque and operating angle based on a stored relationship between the load torque, operating angle, and target behavior index value; means for determining a value, comprising at least the yaw rate of the vehicle, as a behavior index value corresponding to change of behavior of the vehicle; means for controlling the steering actuator such that the determined behavior index value follows the target behavior index value; means for computing a target operating angle of the operating member corresponding to the determined behavior index value, based on a stored relationship between the behavior index value and the target operating angle; and means for controlling the operating actuator such that the determined operating angle follows the computed target operating angle.
According to the constitution of the present invention, the operating angle is generated by the operation of the operating member in accordance with the load torque, which is sum of the control torque outputted by the operating actuator and the operating torque inputted by the driver. This control torque functions so as to do away with the deviation between the operating angle and the target operating angle. Accordingly, in a case in which the operating angle has not attained the target operating angle, the control torque serves as an auxiliary force for the operation of the operating member, and in a case in which the operating angle has exceeded the target operating angle, the control torque serves as a reactive force against the operation of the operating member.
Nakano Shiro
Nishizaki Katsutoshi
Segawa Masaya
Takamatsu Takanobu
Cuchlinski Jr. William A.
Hernandez Olga
Jordan and Hamburg LLP
Koyo Seiko Co. Ltd.
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