Fluid-pressure and analogous brake systems – Speed-controlled – Odd condition or device detection
Reexamination Certificate
1998-12-22
2001-07-17
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Odd condition or device detection
C303S181000, C303S163000
Reexamination Certificate
active
06260935
ABSTRACT:
This application claims priority under 35 U.S.C. Sec. 119 to No. 9-365538 filed in Japan on Dec. 23, 1997 and No. 9-365544 filed in Japan on Dec. 23, 1997, the entire contents of which are herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an unpaved road detection system, wherein it can be determined whether the vehicle is traveling on unpaved roads including a gravel road and a dirt road, and an anti-skid control system having the unpaved road detection system, wherein brake pressure in each wheel brake cylinder is controlled on the basis of the result of the unpaved road detection system.
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, a Japanese Patent Laid-open Publication No. 7-165053 discloses an anti-skid control system which is provided for estimating a desired slip rate, e.g., a slip rate at which a maximum coefficient of friction &mgr; will be obtained, before the coefficient of friction &mgr; of a road will become its maximum value in fact, and controlling the braking force applied to a wheel so as to equalize the actual coefficient of friction to the desired coefficient of friction. In practice, a slip rate is estimated when an acceleration of a wheel will exceed a predetermined value, then a peak of coefficient of friction is calculated on the basis of the wheel acceleration detected a predetermined time later, and then the slip rate at the peak of coefficient of friction is employed as the desired slip rate. In other words, when the variation of the slip rate is large when the acceleration of the wheel has exceeded the predetermined value, it can be estimated that the coefficient of friction will be of almost its peak value, so that the desired slip rate will be set to be of relatively small value, whereas when the variation of the slip rate is small, the desired slip rate will be set to be of relatively large value.
In general, the road for the vehicle can be classified into a smooth road or a rough road, which includes unpaved roads, stone pavement, snow road or the like. The unpaved roads include a gravel road and a dirt road. The dirt road is generally meant by a road of dried soil. The gravel road further includes a sand road, as far as the present invention is concerned. In order to distinguish these various kinds of roads, a detection system for classifying the roads into the smooth road or rough road has been already proposed and practiced. However, no system for determining the unpaved roads including the gravel road and dirt road has been known by now. According to the anti-skid control apparatus on the market, the locking condition of each wheel of the vehicle during the braking operation is controlled on the basis of the road conditions, i.e., smooth or rough. However, it has never been determined whether the vehicle is travelling on the unpaved roads, or not.
According to the anti-skid control system as disclosed in the aforementioned Japanese Patent Laid-open Publication No. 7-165053, the peak of coefficient of friction is estimated on the basis of the wheel acceleration before the coefficient of friction becomes its maximum value. When the vehicle vibrates, however, it is not easy to estimate the peak of coefficient of friction. Especially, on the unpaved roads such as the gravel road and dirt road, the coefficient of friction indicates such a characteristic that the coefficient of friction is gradually increased in response to increase of the slip rate. As a result, it is difficult to estimate the peak of the coefficient of friction, so that the slip rate determined to indicate the peak of the coefficient of friction will be of a relatively large value. Accordingly, it has been required to provide the system for determining the unpaved roads, and the anti-skid control system for controlling the brake pressure in accordance with the output of the unpaved road detection system.
With respect to the anti-skid control operation, it is preferable to provide the braking pressure control when the vehicle is traveling on the gravel road, and the braking pressure control when the vehicle is traveling on the dirt road, separately, rather than the braking pressure control for the unpaved road including the gravel road and dirt road. In the case where the braking pressure control is provided for the gravel road so as to reduce a braking distance, if the same braking pressure control is performed with respect to the dirt road, the vehicle stability might be deteriorated. Or, if the same braking pressure control for the dirt road is performed with respect to the gravel road, the braking distance might be prolonged. However, a system for distinguishing the gravel road from the dirt road has been unknown heretofore.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an unpaved road detection system for properly detecting an unpaved road including a gravel road and a dirt road.
It is another object of the present invention to provide the unpaved road detection system for properly distinguishing the gravel road from the dirt road.
It is a further object of the present invention to provide a system for properly detecting the unpaved road and preventing wheels of a vehicle from being locked during braking operation of the vehicle, by controlling hydraulic braking pressure in each wheel brake cylinder, even if the vehicle is travelling on the unpaved road including the gravel road and dirt road.
In accomplish the above and other objects, the unpaved road detection system includes wheel speed sensors for detecting wheel speeds of wheels of a vehicle, and a vehicle speed detection device for detecting a vehicle speed of the vehicle, to calculate a slip rate on the basis of the wheel speeds and the vehicle speed. A linear acceleration sensor is provided for detecting an acceleration of the vehicle in a longitudinal direction thereof and producing a signal linearly proportional to the detected acceleration. A variation calculation device is provided for calculating a variation of the signal produced by the linear acceleration sensor corresponding to a variation of the slip rate calculated. And, a determination device is provided for comparing the variation of the signal calculated by the variation calculation device with a reference value, and determining that the vehicle is traveling on an unpaved road, if the variation exceeds the reference value.
The slip rate may be calculated on the basis of the minimum value of the wheel speeds of all of the wheels and the vehicle speed. Or, the slip rate may be calculated on the basis of an average speed of the wheel speeds of all of the wheels and the vehicle speed.
Preferably, the variation calculation device is adapted to calculate a difference between a first signal detected by the linear acceleration sensor when the slip rate exceeded a first reference rate, and a second signal detected by the linear acceleration sensor when the slip rate exceeded a second reference rate, to output the difference as the variation. The variation calculation device may be adapted to differentiate a first signal detected by the linear acceleration sensor when the slip rate exceeded a first reference rate, to output the differentiated value as the variation.
The system for detecting the unpaved road may further include a peak detection device which is adapted to detect a peak of the slip rate calculated by the slip rate calculation device. And, the variation calculation device may be adapted to calculate a difference between a first signal detected by the linear acceleration sensor when the slip rate exceeded a first reference rate, and a third signal detected by the linear acceleration sensor when the peak detection device detected the peak of the slip rate, to output the difference as the variation.
It is preferable to provide a system, which is adapted to detect an unpaved road and prevent wheels
Abe Yasuhiro
Banno Masaki
Kato Toshihisa
Kobayashi Yasushi
Kondo Koichi
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Kramer Devon
Oberleitner Robert J.
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