Fluid-pressure and analogous brake systems – Speed-controlled – With yaw control
Reexamination Certificate
1996-06-26
2001-05-29
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
With yaw control
C303S147000, C303S186000
Reexamination Certificate
active
06238018
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for controlling a braking-force distribution in a vehicle. Front and rear wheel braking-force distribution is controlled by regulating a braking liquid pressure ratio for front and rear wheel brakes, based on a difference between front and rear wheel speeds.
2. Description of the Related Art
Techniques for controlling a front and rear wheel braking-force distribution to eliminate the difference between the front and rear wheels, and to achieve an ideal braking-force distribution are conventionally known, from Japanese Patent Publication No.51-26584, Japanese Patent Application Laid-open No.6-144178 and the like.
In such known techniques, optimal braking forces, corresponding to loads applied to front and rear wheels, are provided by conducting the control of the front and rear wheel braking-force distribution to eliminate the difference between the front and rear wheel speeds. This is based on the following principle: when a braking force B is generated for a tire receiving a vertical drag force N from a road surface, a slip rate &lgr; of the tire is represented, simplistically, in a very small region by the following equation:
&lgr;=
K
×(
B/N
)
(wherein K is a constant)
The ideal braking-force distribution is to ensure that the front and rear wheel braking forces are proportional to the vertical drag force. Therefore, the front and rear wheel slip rates &lgr; may be equalized. Thus, if the vehicle speed is represented by V
V
, and the wheel speed is represented by V
W
, the slip rate &lgr; is determined according to the following equation:
&lgr;=(
V
V
−V
W
)/
V
V
Therefore, if the braking-force distribution is controlled so that the front and rear wheel speeds V
W
are equal to each other, the front and rear wheel slip rates &lgr; can be equalized. More specifically, control is conducted so that the rear wheel speed V
W
is equal to the front wheel speed V
W
by controlling the braking liquid pressure for the rear wheels.
In the known techniques, however, the behavior of the entire vehicle is not taken into consideration, and depending upon the operational state of the vehicle, there is a room for improvement in an aspect of steerage stability performance, especially, during braking when the vehicle is abruptly turning.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a process for controlling the braking-force distribution in a vehicle, wherein a sudden increase in yaw rate is inhibited during braking during a sudden turn of the vehicle, thereby further enhancing the steerage stability performance.
To achieve the above object, according to the present invention, there is provided a process for controlling a braking-force distribution in a vehicle. Front and rear wheel braking-force distribution is controlled by regulating a braking liquid pressure ratio for front and rear wheel brakes, based on a difference between front and rear wheel speeds. The process comprises the steps of: detecting whether the vehicle is in an abrupt turning state; and decreasing the braking liquid pressure distribution ratio for the rear brakes when the abrupt turning state is detected, as compared with the case where the abrupt turning state is not detected.
With such a feature of the present invention, when braking during a sudden turn of the vehicle, the braking force for the rear wheels is suppressed, whereby a reduction in lateral force to the tires of the rear wheels can be prevented to inhibit a sudden increase in yaw rate, thereby insuring stability of the vehicle.
According to another aspect and feature of the present invention, the abrupt turning state of the vehicle is detected based on comparison of a) a differentiation value of a product of a vehicle speed and a yaw rate of a vehicle body with b) a preset value. Thus, it is possible to accommodate the variation in physical limit of the yaw rate in accordance with the vehicle speed by detecting an abrupt turning state of the vehicle based on the differentiation value of the product of the vehicle speed and the yaw rate of the vehicle body. Especially, during high-speed traveling in which the physical limit of the yaw rate is lowered, the stability of the vehicle can be effectively insured.
According to a further aspect and feature of the present invention, the vehicle speed is presumed based on at least one of the front wheel speeds and the rear wheel speeds, and the yaw rate of the vehicle body is presumed based on a difference between the left and right rear wheel speeds. Thus, an expensive sensor for directly detecting the yaw rate is not required. In addition, when gripping of a rear one of the inner wheels, as viewed during turning of the vehicle, approaches a limit so that slipping starts to increase, the presumed value of the yaw rate provided using the left and rear wheel speeds is suddenly increased. Therefore, a critical situation of the rear wheel tires can be detected more sensitively than the direct detection of the yaw rate which is a variation in behavior of the vehicle body, and thus, control can be started immediately.
According to a yet further aspect and feature of the present invention, a rear wheel deceleration is calculated based on the rear wheel speeds. The regulation of the braking liquid pressure distribution ratio is carried out under a condition that the rear wheel deceleration exceeds a preset value. Thus, unnecessary control can be more effectively inhibited by defining a timing for starting the regulation of the front and rear wheel braking-force distribution depending upon the situation of the rear wheel tires.
The above and other objects, features and advantages of the invention will become apparent from the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4881785 (1989-11-01), Ushijima et al.
patent: 5021957 (1991-06-01), Yoshino et al.
patent: 5150951 (1992-09-01), Leiber
patent: 5211453 (1993-05-01), Van Zanten et al.
patent: 5375917 (1994-12-01), Inagaki
patent: 5407259 (1995-04-01), Itabashi et al.
patent: 5551771 (1996-09-01), Akuzawa et al.
patent: 4208581A1 (1993-05-01), None
patent: 4226646A1 (1994-02-01), None
patent: 51-26584 (1976-08-01), None
patent: 404257757 (1992-09-01), None
patent: 6-144178 (1994-05-01), None
patent: 6-156249 (1994-06-01), None
Kubonoya Hideki
Sugimoto Yoichi
Urai Yoshihiro
Arent Fox Kintner & Plotkin & Kahn, PLLC
Graham Matthew C.
Honda Giken Kogyo Kabushiki Kaisha
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