Fluid-pressure and analogous brake systems – Speed-controlled – Specific mu determination
Reexamination Certificate
1999-12-23
2001-03-20
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Specific mu determination
C188S18100R, C701S080000, C303S177000
Reexamination Certificate
active
06203121
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coefficient of friction peak estimation apparatus for estimating the peak of a coefficient of friction in a coefficient of friction—slip rate characteristic, and relates to an anti-skid control system having the coefficient of friction peak estimation apparatus to control a hydraulic braking pressure in each wheel brake cylinder in response to a wheel speed detected when the peak of the coefficient of friction is estimated.
2. Description of the Related Arts
Various anti-skid control systems have been proposed heretofore to prevent a wheel from being locked during a braking operation of a vehicle. For example, Japanese Patent Laid-open Publication No.8-150918 discloses an anti-skid control system which is adapted to compare a wheel acceleration with a vehicle acceleration at a predetermined time, and adjust a pressure increasing rate of braking pressure, based upon the result of comparison. According to that publication, in view of a prior anti-skid control system as disclosed in Japanese Patent Laid-open Publication No.4-345567, which was aimed to provide an appropriate pressure increasing rate in accordance with the slip rate under such a condition as the coefficient of friction of a road (abbreviated as a road &mgr;) or the like is constant, thereby to achieve an ideal braking force control, it was proposed to solve such a problem that the ideal braking force control could not necessarily be achieved by that prior anti-skid control system, when the condition such as the coefficient of friction of the road was varied, so that it is aimed to control the braking force in accordance with the coefficient of friction of the road.
Furthermore, in Japanese Patent Laid-open Publication No.8-295223, there is disclosed a vehicle speed estimation apparatus which is provided with means for determining whether a changing point of a property in a road coefficient of friction—slip rate characteristic was crossed, and adapted to change the estimation of a vehicle speed into the estimation of the vehicle speed on the basis of an estimated vehicle deceleration calculated by vehicle speed estimation means, and also disclosed is the anti-skid brake system having the vehicle speed estimation apparatus.
According to the vehicle speed estimation apparatus as disclosed in the above Japanese Patent Laid-open Publication No.8-295223, it is determined on the basis of a varying rate (&Dgr;dVw) of a wheel acceleration as shown in FIGS. 8 and 9 of that publication, whether the changing point of the property (corresponding to the peak) of the coefficient of friction—slip rate characteristic was crossed. According to that apparatus, in the case where the variation around the peak in the road coefficient of friction—slip rate characteristic is large, the peak can be identified. In the case where the variation around the peak is small, however, the varying rate (&Dgr;dVw) of the wheel acceleration is necessarily small, so that it will be difficult to distinguish the peak. This is resulted from not only road conditions, but also tire properties. For example, the variation around the peak in case of a tire without studs (i.e., stud-less tire) is so small that it will be difficult to distinguish the peak.
In the meantime, the aforementioned Japanese Patent Laid-open Publication No.8-150918 never discloses the estimation of the peak in the coefficient of friction—slip rate characteristic, nor suggests it.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a coefficient of friction peak estimation apparatus for estimating the peak of a coefficient of friction in a coefficient of friction—slip rate characteristic surely.
It is also an object of the present invention to provide an anti-skid control system for estimating the peak of the coefficient of friction surely, and performing a braking force control appropriately on the basis of the estimated peak.
In accomplish the above object, the coefficient of friction peak estimation apparatus includes a wheel acceleration detection device for detecting a wheel acceleration of each wheel of a vehicle, a vehicle acceleration detection device for detecting a vehicle acceleration of the vehicle, and a peak estimation device for estimating the peak of a coefficient of friction in a coefficient of friction—slip rate characteristic. The peak estimation device is adapted to determine that the coefficient of friction is the peak, when the wheel acceleration is lower than the vehicle acceleration, by more than a predetermined difference.
The apparatus for estimating a peak of coefficient of friction may further include a wheel speed detection device for detecting a wheel speed of each wheel of the vehicle. The wheel acceleration detection device may include a wheel acceleration calculating device which differentiates the wheel speed detected by the wheel speed detection device to obtain the wheel acceleration of each wheel of the vehicle, and the vehicle acceleration detection device may include vehicle speed calculating device which calculates an estimated vehicle speed of the vehicle on the basis of the wheel speed of each wheel detected by the wheel speed detection device, and vehicle acceleration calculating device which differentiates the estimated vehicle speed calculated by the vehicle speed calculating device to obtain the vehicle acceleration of the vehicle.
An anti-skid control system for an automotive vehicle may be formed to include a wheel brake cylinder operatively mounted on each wheel of the vehicle, a pressure generating device for pressurizing brake fluid in response to operation of a manually operated member to generate a hydraulic braking pressure and supply the hydraulic braking pressure to the wheel brake cylinder, and a pressure control device disposed between the wheel brake cylinder and the pressure generating device. The pressure control device is provided for controlling the hydraulic braking pressure in the wheel brake cylinder in accordance with a braking condition of the vehicle. In the anti-skid control system, a wheel speed detection device may be provided for detecting a wheel speed of each wheel of the vehicle, and a wheel acceleration calculating device may be provided for differentiating the wheel speed detected by the wheel speed detection device to obtain the wheel acceleration of each wheel of the vehicle. Then, a vehicle speed calculating device may be provided for calculating an estimated vehicle speed of the vehicle on the basis of the wheel speed of each wheel detected by the wheel speed detection device, and a vehicle acceleration calculating device may be provided for differentiating the estimated vehicle speed calculated by the wheel speed calculating device to obtain the vehicle acceleration of the vehicle. And, a peak estimation device is provided for estimating the peak of a coefficient of friction in a coefficient of friction—slip rate characteristic. The peak estimation device is adapted to determine that the coefficient of friction is the peak when the wheel acceleration calculated by the wheel acceleration calculating device is lower than the vehicle acceleration calculated by the vehicle acceleration calculating device, by more than a predetermined difference. Furthermore, a reference speed setting device is provided for setting a reference speed for initiating a pressure decrease mode on the basis of the wheel speed detected by the wheel speed detection device and the estimated vehicle speed calculated by the vehicle speed calculating device, when the peak estimation device estimated the peak of the coefficient of friction. Accordingly, the pressure control device is adapted to be controlled in response to at least the result of comparison between the reference speed set by the reference speed setting device and the wheel speed detected by the wheel speed detection device.
REFERENCES:
patent: 3871715 (1975-03-01), Hikida et al.
patent: 4779447 (1988-10-01), Rath
patent: 4855917 (1989-08-01), Sawa
Abe Yasuhiro
Kato Toshihisa
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Butler Douglas C.
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