Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2000-04-25
2001-10-23
Camby, Richard M. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S042000, C180S410000
Reexamination Certificate
active
06308122
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a steering system for a motor vehicle, which is capable of variably setting a relationship between the steering of steerable vehicle wheels and the operation of an operation mechanism such as a steering wheel.
2. Description of Related Art
A steering system for a motor vehicle has been proposed in which a steering wheel is mechanically disengaged from a steering mechanism for steering vehicle wheels (see, for example, U.S. Pat. No. 5,908,457). This system is adapted to detect the direction and amount of the operation of the steering wheel and apply a driving force from an actuator such as an electric motor to the steering mechanism on the basis of the results of the detection.
This arrangement obviates the need for mechanical coupling between the steering mechanism and the steering wheel, so that upward thrust of the steering wheel can be prevented at collision of the motor vehicle. Further, this arrangement allows for structural simplification and weight reduction of the steering mechanism, and more flexible placement of the steering wheel. Moreover, this arrangement makes it possible to employ other operation mechanisms such as a steering lever and a steering pedal instead of the steering wheel.
In such a motor vehicle steering system, a relationship between the operation of the steering wheel and the operation of the steering mechanism can flexibly be changed through an electrical control. Thus, the maneuverability of the motor vehicle is expected to be drastically improved.
In the case of an ordinary motor vehicle in which a steering wheel and a steering mechanism are mechanically coupled to each other, for example, the dynamic characteristics of the motor vehicle responsive to the steering (over-steering, under-steering, neutral-steering and the like) are virtually determined by various factors (weight, wheel base, gravity center and the like) of the motor vehicle. The motor vehicle is generally designed so as to be driven in a slightly under-steered state.
However, the dynamic characteristics of the motor vehicle vary depending upon the number of passengers and a load on the motor vehicle. As the total weight of the motor vehicle increases, the tendency toward the under-steering generally increases to reduce the steering response of the motor vehicle. That is, the motor vehicle is less easy to corner.
Further, the dynamic characteristics vary from one motor vehicle to another. Therefore, a driver is often confused when driving a motor vehicle other than his familiar motor vehicle, and it takes some time for him to become accustomed to the driving of the motor vehicle.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a steering system for a motor vehicle which is capable of effecting a proper behavioral change of the motor vehicle in response to a steering operation.
It is a specific object of the invention to provide a steering system for a motor vehicle which is capable of effecting a predetermined behavioral change of the motor vehicle in response to a steering operation.
It is another specific object of the invention to provide a steering system for a motor vehicle which is capable of stabilizing the behavior of the motor vehicle at cornering by complementing the driving skill of a driver.
It is further another specific object of the invention to provide a steering system for a motor vehicle which allows a motor vehicle to have dynamic characteristics according to a driver's preference.
In accordance with one aspect of the invention, there is provided a steering system for a motor vehicle, which comprises: a behavioral variable computation section for performing computation on a predetermined behavioral variable indicative of a behavior of the motor vehicle; and a steering angle controlling section for sequentially updating a relationship between a steering angle of vehicle wheels and an operation angle of an operation mechanism on the basis of a value of the behavioral variable computed by the behavioral variable computation section and a preset target value of the behavioral variable, and controlling a steering mechanism on the basis of the updated relationship.
The behavioral variable may include, for example, a steady-state gain which is a steady-state ratio of the steering angle (actual steering angle) of the vehicle wheels to the operation angle. The steady-state gain can be determined on the basis of the operation angle and a lateral acceleration.
The behavioral variable may include a time constant indicative of a followability (responsiveness) of a change in the steering angle of the vehicle wheels to a change in the operation angle. The time constant can be determined by detecting a phase difference between the operation angle and the steering angle of the steering mechanism.
The steering angle controlling section is preferably adapted to update the relationship between the steering angle of the vehicle wheels and the operation angle of the operation mechanism to minimize a difference between the value of the behavioral variable indicative of an actual behavior of the motor vehicle and the target value of the behavioral variable.
In accordance with the present invention, the update of the relationship between the steering angle of the vehicle wheels and the operation angle of the operation mechanism allows the motor vehicle to behave in accordance with the target value of the behavioral variable. Thus, any motor vehicle incorporating the steering system can have constant dynamic characteristics, so that a driver becomes accustomed to the dynamic characteristics of the motor vehicle from the beginning even if that motor vehicle is not his familiar motor vehicle.
In accordance with another aspect of the invention, there is provided a steering system for a motor vehicle, which comprises: a steering correction amount detecting section for detecting a correction amount of a steering operation at cornering; and a steering controlling section for updating a relationship between a steering control of vehicle wheels and an operation amount of an operation mechanism on the basis of the correction amount of the steering operation detected by the steering correction amount detecting section, and controlling a steering mechanism on the basis of the updated relationship.
The correction amount of the steering operation can be determined, for example, by detecting the operation amount of the operation mechanism by means of an operation amount detecting section (e.g., operation angle detector such as rotary encoder) and calculating an overshoot occurring before the operation amount is restored to a steady-state level after the cornering. The relationship between the steering control of the vehicle wheels and the operation amount may be updated on condition that the overshoot in an operation amount change exceeds a predetermined level.
The correction amount of the steering operation may be determined, for example, by calculating an overshoot occurring before a yaw angle change of the motor vehicle or a lateral positional offset of the motor vehicle (a positional offset with respect to a direction perpendicular to a traveling direction of the motor vehicle, i.e., a widthwise positional offset of the motor vehicle) is restored to a steady-state level after the cornering. The relationship between the steering control of the vehicle wheels and the operation amount may be updated on condition that the overshoot in the yaw angle change or the lateral positional offset of the motor vehicle exceeds a predetermined level.
A driver unskilled in driving tends to return a steering wheel with a time delay at the final stage of the cornering at an intersection. Therefore, the driver has to correct the steering operation, so that the motor vehicle is laterally staggered. In the invention, the control of the steering mechanism is properly varied according to the correction amount of the steering operation, whereby smooth cornering is ensured to stabilize the behavior
Nishizaki Katsutoshi
Segawa Masaya
Takamatsu Takanobu
Camby Richard M.
Koyo Seiko Co., Ltd
Rabin & Berdo P.C.
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