Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-07-13
2002-05-28
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S041000, C701S042000, C701S070000, C180S193000, C180S193000, C180S193000, C303S122000, C303S146000
Reexamination Certificate
active
06397135
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based on and claims priority under 35 U.S.C §119 with respect to Japanese Patent Application 2000-384150, filed on Dec. 18, 2000 and Japanese Patent Application 2000-212992, filed on Jul. 13, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a rear-wheel steering angle control device which can improve the running stability of a vehicle with steering rear-wheels as well as front-wheels, in particular, a rear-wheel steering angle control device which can prevent the occurrence of the swing-out at the rear edge portion of the vehicle on condition that the rear-wheel is steered in counter direction to the front-wheel steering angle.
2. Description of the Related Art:
Hitherto, a rear-wheel steering angle control device is known which can improve the running stability of a vehicle and the capability of a small turning circle with steering rear-wheels as well as front-wheels. According to this rear-wheel steering angle control device, it becomes a subject of discussion of how the optimum target rear-wheel steering angle should be relative to the front-wheel steering angle corresponding to every driving condition of the vehicle. For example, in column “7.5.3 4WS control for zero skid” at page 196 of a publication (this publication will be hereafter referred to as “publication No.1”) entitled “Steering and Dynamics” (date of publication of the first edition: Sep. 10, 1996, publishing office: SANKAIDO, Inc., author: KAYABA KOUGYO, Inc.), the following is disclosed. The body slip angle (deviation angle between running direction of the vehicle and longitudinal direction of the vehicle) is focused on. When the vehicle speed is lower than a predetermined vehicle speed, the rear-wheel steering angle is controlled in a counter direction to the front-wheel steering angle in proportion to the front-wheel steering angle to obtain the capability of the small turning circle. Also when the vehicle speed is greater than a predetermined vehicle speed, the rear-wheel steering angle is controlled in the same direction as the front-wheel steering angle in proportion to the front-wheel steering angle in order to obtain the ideal vehicle dynamics which has the superior driving stability of the vehicle (this type of the control will be referred to as “proportional steering angle control” hereafter).
However, when the proportional steering angle control as shown in publication No.1 is operated under a low range of the vehicle speed as the vehicle leaves, the rear-wheels are steered in a counter direction to the front-wheel steering angle. Therefore, the capability of the small turning circle is improved. However, there is a problem in that the rear edge portion of the vehicle (in particular, the corner portion of the rear edge of the vehicle) swings out and causes the vehicle to touch an obstacle at the side of the vehicle.
Therefore, in order to solve the problem of this swing-out at the rear edge portion of the vehicle and obtain the capability of the small turning circle as well, a means that controls the rear-wheel steering angle so that the rear edge portion of the vehicle follows the running locus of the front end point of the vehicle is proposed, for example, in column “105 a reduction control means of swing-out of the 4WS vehicle” of publication entitle (this publication will be referred to as “publication No.2 ” hereinafter) “The proceedings of Japanese Society of Automotive engineering 882, October, 1988”. That is, the running locus of the front end point at every predetermined sampling interval is memorized as sample points, and the rear-wheel steering angle is controlled so that a running direction of the front end point at a nearest sample point which, is the nearest point to the then rear end point among the whole sample points, becomes equal to a running direction of the then rear end point.
However, in the case when this control means, as disclosed in publication No. 2, is employed, it is known that when a steering wheel is being steered just after the vehicle leaves the rear-wheel steering angle is controlled in the same direction to the front-wheel steering angle for a short while and subsequently is controlled in counter direction to the front-wheel steering angle (see the area C of FIG.
17
). The occurrence of this matter causes a driver of the vehicle to experience a feeling of wrongness and also increases the energy needed to steer the rear-wheels with uselessly steering the rear-wheels extra.
Also, as for the usual 4WS vehicle, because the controllable range of the rear-wheel steering angle is smaller than the practicable range of the front-wheel steering angle, the rear edge portion of the vehicle can not always be forced to follow the running locus of the front end point of the vehicle. Therefore, when this control means as disclosed in the publication No.2 is applied, there is a problem such that the vehicle runs with the rear-wheels steered in the same direction as the front-wheel steering angle (a state where a deviation between the then rear end point and the nearest sample point remains continuously) under the low range of the vehicle speed, which deteriorates the turning performance of the vehicle (see FIG.
21
). Hereinafter, this state will be referred to as “the crab-like running state”.
In order to prevent the occurrence of this state as mentioned above, it is necessary to expand the controllable range of the rear-wheel steering angle to the same extent as the practicable range of the front-wheel steering angle. However, expanding the controllable range of the rear-wheel steering angle is difficult in view of the steering mechanism and the space, and causes deterioration of the steering feeling of the driver.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention is to present a rear-wheel steering angle control device which can cope with both the improvement of the capability of the small turning circle and the reduction of the swing-out at the rear edge portion of the vehicle under a low range of vehicle speed which are contrary to each other, and does not provide a feeling of wrongness for the driver of the vehicle.
In order to achieve the object, there is provided a rear-wheel steering angle control device comprising 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 on the basis of the output of the detecting means and the target rear-wheel steering angle calculating means including a mileage detecting means for detecting a mileage reckoned from a leaving time of the vehicle; a rear-wheel steering angle control means for controlling the actual rear-wheel steering angle detected by the detecting means so that the actual rear-wheel steering angle becomes equal or approximately equal to the target rear-wheel steering angle, wherein the target rear-wheel steering angle calculating means calculates the target rear-wheel steering angle by means of a transitional control until the mileage reckoned from the leaving time reaches a predetermined mileage and calculates the target rear-wheel steering angle by means of a regular control after the mileage reckoned from the leaving time reaches the predetermined mileage, wherein the regular control is a control that the target rear-wheel steering angle is calculated in counter direction to the actual front-wheel steering angle at least when the vehicle speed is lower than a predetermined speed, and the transitional control is a control that a temporary target rear-wheel steering angle calculated on the assumption that the regular control is applied is normally employed as the target rear-wheel steering angle, and under a predetermined condition the target rear-wheel steering angle is calculated so that the target rear-wheel steering angle reaches to the
Aisin Seiki Kabushiki Kaisha
Cuchlinski Jr. William A.
To Tuan C
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