Fluid-pressure and analogous brake systems – Speed-controlled – With failure responsive means
Reexamination Certificate
2002-08-16
2004-01-27
Butler, Douglas C. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
With failure responsive means
C303S122000, C701S034000, C701S076000
Reexamination Certificate
active
06682153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for detecting an output-stuck fault of a car body acceleration sensor installed in a car having an anti-lock braking system for a car, an apparatus for detecting the output-stuck fault of the car body acceleration sensor, the anti-lock braking system for a car, and a program for detecting the output-stuck fault of the car body acceleration sensor.
2. Description of the Related Art
It is possible to obtain a wheel deceleration signal necessary for the control of an anti-lock braking system (hereinafter, referred to as an “ABS”) of a two-wheel drive car having undriven wheels easily. However, if a center differential and a rear wheel shaft differential are locked and four wheels are in the state of being directly connected with each other in a four-wheel drive car, all of the wheels are connected with an engine having a large moment of inertia. Consequently, the response speeds of the wheels to the changes of braking torque are remarkably decreased. Hence, it is almost impossible to obtain any wheel deceleration signals, and thereby the wheels are locked.
As one of means for solving such a problem, a four-wheel drive car is generally provided with a car body acceleration sensor. The four-wheel drive car measures car body acceleration in a traveling direction of the car body with the car body acceleration sensor, and judges that a road surface is one having a low value of frictional resistance &mgr; (hereinafter, referred to as a “low &mgr; road surface”) when deceleration at the time of braking is smaller than a fixed value. Then, the four-wheel drive car switches the slip control logic of its ABS from that for a road surface having a high value of frictional resistance &mgr; (hereinafter, referred to as a “high &mgr; road surface”) to that for a low &mgr; road surface to increase the control accuracy of the ABS. Thereby, the four-wheel drive car prevents the locking of its wheels.
Consequently, the car body acceleration sensor is indispensable to the ABS of a four-wheel drive car. If the car body acceleration sensor is broken down, there is the possibility that the slip control of the car becomes impossible to make the wheels be locked. Therefore, the fault detection of the car body acceleration sensor can be concluded to be indispensable. Several fault modes can be supposed as the fault modes of a car body acceleration sensor. One of them is an output-stuck fault by which the car body acceleration output signal does not follow the acceleration of the car body and not to change with a fixed car body acceleration signal being output.
As first prior art for detecting an output-stuck fault of a car body acceleration sensor, a technique disclosed in a Japanese Patent Laid-Open Publication No. Hei 1-195168 is known. By the disclosed technique, the car body acceleration operated on the basis of an output of a wheel speed sensor is compared with the car body acceleration detected by the car body acceleration sensor when the control of an ABS is not performed. If the result of the comparison is a predetermined value or more, the car body acceleration sensor is judged to be in its output-stuck fault state.
However, for example, when a car ascends or descends a sloping road having a large angle of inclination, there is the possibility that a large difference is produced between the car body acceleration operated on the basis of an output of the wheel speed sensor and the car body acceleration detected by the car body acceleration sensor, though the car body acceleration sensor is normal. Consequently, there is the possibility that an output-stuck fault is erroneously detected.
Moreover, as second prior art that solves the defect of the first prior art, a technique disclosed in Japanese Patent Laid-Open Publication No. Hei 8-184610 is known. By the disclosed technique, the car body acceleration to work on a car body by the gravity supposed to be applied to the car body when the car ascends or descends a sloping road having a sufficiently large angle of inclination is set to be a threshold value. And, when the car body acceleration operated on the basis of an output of the wheel speed sensor of the car is larger than the set threshold value and the car body acceleration detected by the car body acceleration sensor is smaller than the threshold value, the car body acceleration sensor of the car is judged to be in its output-stuck fault state. Moreover, the following conditions are defined as the other conditions for the judgment of the car body acceleration sensor being in its output-stuck fault: the control of the ABS of the car is not performed; the car body is traveling; and the speed differences of a plurality of wheels are a predetermined speed difference.
As it is described above, in the above-mentioned second prior art, the car body acceleration to work on the car body by the gravity at the time when the car ascends or descends the sloping road having the sufficiently large angle of inclination is set to be the threshold value, and thereby it is prevented to detect the output-stuck fault erroneously at the time when the car ascends or descends the sloping road having the large angle of inclination though the car body acceleration sensor is normal.
However, by the above-mentioned second prior art, an output-stuck fault of a car body acceleration sensor can be detected only when a car ascends or descends a sloping road having a sufficiently large angle of inclination, or only when the car body acceleration corresponding to such a case works on a car body. And, for example, when a car travels on a flat low &mgr; road surface, the car body acceleration working on the car body of the car is small. Consequently, there is the possibility that, even if an output-stuck fault of the car body acceleration sensor occurs, the output-stuck fault cannot be detected by the prior art and thereby the ABS for a car does not operate normally.
SUMMARY OF THE INVENTION
The present invention was made in view of such situations, and the invention aims to provide a method for detecting an output-stuck fault of a car body acceleration sensor, an apparatus for detecting an output-stuck fault of a car body acceleration sensor, an anti-lock braking system for a car, and a program for detecting an output-stuck fault of a car body acceleration sensor wherein the method, the apparatus, the system and the program do not erroneously detect any output-stuck fault when a car ascends or descends a sloping road having a large angle of inclination though the car body acceleration sensor is normal and can exactly detect any output-stuck faults of the car body acceleration sensor even in the situation in which car body acceleration working on the car body is small.
A first aspect of the present invention is for achieving the above-mentioned object, and the aspect is a method for detecting an output-stuck fault of a car body acceleration sensor installed in a car having an ABS for a car, the method comprising the steps of: operating a relative acceleration difference between the logical car body acceleration operated on the basis of a wheel speed and the physical car body acceleration detected by the car body acceleration sensor; measuring a duration time of a state in which the acceleration difference is exceeding a rated value &agr;; storing the minimum acceleration and the maximum acceleration of the physical car body acceleration during the state in which the acceleration difference is exceeding the rated value &agr;; and judging that the car body acceleration sensor is in its output-stuck fault state if a difference between the stored minimum acceleration and the stored maximum acceleration is a rated value &bgr; or less at the point of time when the duration time of the state in which the acceleration difference is exceeding the rated value &agr; exceeds a rated time.
In the method for detecting an output-stuck fault of a car body acceleration sensor of the first aspect, at first, the relative acceleration difference betwee
Bosch Automotive Systems Corporation
Butler Douglas C.
Priest & Goldstein PLLC
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