Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-08-09
2003-05-27
Black, Thomas G. (Department: 3663)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S070000, C280S005510, C280S211000, C280S263000, C280S426000, C280S099000, C180S408000, C180S234000, C180S193000
Reexamination Certificate
active
06571160
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to a rear-wheel steer control device which steers rear wheels in addition to front wheels, depending on vehicle motion conditions, for improving vehicle stability and so on. More particularly, the present invention is directed to reduce man-hours required for setting a target rear-wheel steering angle of the device.
BACKGROUND OF THE INVENTION
It is well known that some vehicles possess a rear-wheel steering angle control device which steers rear wheels in addition to front wheels, depending on vehicle motion conditions, for improving vehicle stability and so on. In such a rear-wheel steer control device, a question is raised as to how to cope with setting an optimal target steering angle relative to a front steering angle depending on various vehicle motion conditions. To solve this question, a publication whose title is ‘Steering System and Steering Stability for Vehicles’ and which is published as the first version by SANKAIDO publishing on Sep. 10, 1996 provides an idea on page 196, titled ‘17.5.3 4WS control for zeroizing side skid’ which says that while the vehicle-body slip angle (i.e. a deviation angle between the vehicle travel direction and the vehicle lengthwise direction) is focused, controlling the rear-wheel steering angle continually to reducing the vehicle slip angle to zero makes it possible to obtain an ideal vehicle dynamics with excellent vehicle stability.
However, conducting a road test according to the teaching of the aforementioned ‘4WS control for zeroizing side skid’ reveals that the gain of the target rear-wheel steering angle relative to the front-wheel becomes too large, thereby giving an uncomfortable feeling to an ordinary driver. Thus, the aforementioned ‘4WS control for zeroizing side skid’ is found not to be practical and therefore, the optimal gain of the target rear-wheel steering angle relative to the front-wheel steering angle is set in trial and error fashion based on various vehicle dynamics derived from road test results.
In addition, though Japanese Patent Publication No. Sho. 60 (1985)-44185 discloses a rear-wheel steering angle control device in which a gain of a target rear-wheel steering angle relative to a front-wheel steering angle is made variable depending on vehicle speed, this reference remains silent as to how to set the gain of the target rear-wheel steering angle relative to the front-wheel steering angle. This means that there is no change in requiring an extreme amount of man-hours in setting the gain.
Thus, a need exists to provide a rear-wheel steer control device which drastically reduces the man-hours required for setting a gain of a target rear-wheel steering angle relative to a front-wheel steering angle.
SUMMARY OF THE INVENTION
The present invention has been developed to satisfy the request noted above and a first aspect of the present invention provides a rear-wheel steer control device which comprises a detecting means for detecting at least a vehicle speed, an actual front-wheel steering angle, and an actual rear-wheel steering angle; a target rear-wheel steering angle calculating means for calculating a target rear-wheel steering angle based on at least outputs of the detecting means; and a rear-wheel steering angle controlling means for controlling the actual rear-wheel steering angle detected by the detecting means to become equal or approximately equal to the target rear-wheel steering angle calculated by the target rear-wheel steering angle calculating means. Further, the target rear-wheel steering angle calculating means includes a variable coefficient inputting means for inputting variable coefficients and an inverse operation setting means in which a specific physical quantity which represents a vehicle motion is dealt with when a transfer function of the rear-wheel steering angle relative to the front-wheel steering angle is set and as a target transfer function a transfer function is employed which is obtained by multiplying specific parameters of a theoretical transfer function of the specific physical quantity relative to the front-wheel steering angle by the variable coefficients inputted from the variable coefficient inputting means. When an equivalent transfer function of the specific physical quantity relative to the front-wheel steering angle is represented by a transfer function of the rear-wheel steering angle relative to the front-wheel steering angle, a theoretical transfer function of the specific physical quantity relative to the front-wheel steering angle, and a theoretical transfer function of the specific physical quantity relative to the rear-wheel steering angle, the transfer function of the rear-wheel steering angle relative to the front-wheel steering angle is inversely calculated so that the equivalent transfer function becomes equivalent to the target transfer function. Moreover, the target rear-wheel steering angle calculating means calculates the target rear-wheel steering angle based on the transfer function of the rear-wheel steering angle relative to the front-wheel steering angle as calculated by the inverse operation setting means.
In the preceding description, as the ‘specific physical quantity which represents a vehicle motion’, vehicle-body slip angle, yaw rate, or lateral acceleration, etc. is available. The ‘theoretical transfer functions’ are various theoretical formulas of transfer functions which are derived from ‘control theory’ when an adequate vehicle dynamics model is assumed. The ‘specific characteristic parameter’ of the theoretical transfer function is each of the various parameters which appear in the calculated theoretical transfer functions. An example of the ‘specific characteristic parameter’ related to static characteristic is the steady gain of a specified physical quantity, while examples of the ‘specific characteristic parameter’ related to dynamic characteristic are natural angular frequency, damping or attenuation ratio, leading item, and so on.
In accordance with the first aspect of the present invention, the target rear-wheel steering angle calculating means calculates the target rear-wheel steering angle based on the transfer function of the rear-wheel steering angle relative to the set front-wheel steering angle, in such a manner that the theoretical transfer function of the specific physical quantity relative to the front-wheel steering angle is derived, in order to obtain transfer functions as target transfer functions by multiplying the specific characteristic parameters which appear in the theoretical transfer function with various variable coefficient inputted from the variable coefficient inputting means. Further, the equivalent transfer function of the specific physical quantity, relative to the front-wheel steering angle, is represented by three transfer functions: the transfer function of the rear-wheel steering angle relative to the front-wheel steering angle, the theoretical transfer function of the physical quantity relative to the front-wheel steering angle, and the theoretical transfer function of the physical quantity relative to the rear-wheel steering angle. The transfer function of the rear-wheel steering angle relative to the front-wheel steering angle is set by the inverse operation setting means.
Thus, the set transfer function of the rear-wheel steering angle relative to the front-wheel steering angle is represented in a form which includes the various variable coefficients inputted from the variable coefficient inputting means to be multiplied with the specific parameter, which makes it possible, when each of the various variable coefficients is tuned, to tune the gain of the rear-wheel steering angle relative to front-wheel steering angle. It is to be noted that tuning each of the various variable coefficients brings in tuning each of the specific characteristic parameters which appear in the theoretical transfer function of the physical quantity relative to the front-wheel steering angle, thereby enabling to tune each of the characteristic parameters
Aisin Seiki Kabushiki Kaisha
Black Thomas G.
Sughrue & Mion, PLLC
To Tuan C
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