Fluid-pressure and analogous brake systems – Speed-controlled – Specific mu determination
Reexamination Certificate
1999-01-21
2002-03-12
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Specific mu determination
C303S112000, C303S154000, C303S178000
Reexamination Certificate
active
06354675
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ABS (Antilock Brake System) apparatus for preventing wheels from being locked when quick braking is applied to a car.
BACKGROUND ART
A typical prior art ABS apparatus controls braking on a car wheel as follows. Specifically, the wheel is attached with a hub formed with gear teeth. When the gear teeth turn, the turning is detected by an electromagnetic pick up, and based on information detected by the electromagnetic pick up, a wheel speed is calculated. Next, a car speed is calculated from the wheel speed and signals from an acceleration sensor. Further, a slip rate is calculated from the wheel speed and the car speed, and this slip rate is used for controlling the braking on the wheel.
In such a system, it is very difficult to directly obtain the car speed, and therefore the car speed must be estimated from the wheel speed and the signals from the acceleration sensor. More specifically, it is impossible to obtain an accurate car speed, and as a result the control is inaccurate.
Further, when the car speed is slower, a pick-up cycle of the electromagnetic pick becomes accordingly longer, making the control more inaccurate. This problem is a serious shortcoming in the ABS apparatus since the ABS apparatus must keep performing from the time the car speed begins to decrease after a brake pedal is pressed to the time the car comes to a complete stop.
In order to solve the above problem, the inventor of the present invention proposed on ABS apparatus (Japanese Patent Laid-Open-9-2240) in which a differential parameter M according to a difference between road frictional force F and braking torque T is used in the control. Specifically, the ABS apparatus begins to reduce braking pressure when the differential parameter M decreases to a predetermined threshold while a brake is being applied.
However, the above ABS apparatus disclosed in the Japanese Patent Laid-Open 9-2240 does not make any proposal concerning control on a time for stopping the pressure reducing operation in the braking equipment. Further, no detailed proposal is made for control on varying the threshold for matching the timing for starting or stopping the pressure reducing operation concurrently with change in car speed and road conditions. Still further, no proposal is made for detecting or dealing with an over slip caused when the threshold value for starting or stopping the pressure reducing operation deviates from an ideal value.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide an ABS apparatus capable of controlling accurately regardless of change in the car speed or road conditions.
According to a first aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; and a differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors. The ABS apparatus further comprises a brake fluid pressure controlling means for starting and then stopping a pressure reducing operation when the differential parameter M calculated by the differential parameter calculating means reaches a first threshold provided according to a peak value of the differential parameter M or a second threshold having an absolute value slightly smaller than that of the first threshold while the braking equipment is in operation.
According to a preferred embodiment of the present invention, the differential parameter calculating means obtains a value F-T as the differential parameter M by subtracting the braking torque T from the road frictional force F based on the braking torque information and road frictional force information from the first sensors.
According to another preferred embodiment of the present invention, the differential parameter calculating means obtains a value (R/r)F-T as the differential parameter M based on the braking torque information and road frictional force information from the first sensors; where R is a radius of the wheel, and r is a distance from a center of turning in the wheel to a braking calipers of the braking equipment. The differential parameter M is obtained by having a ratio of the radius R to the distance r multiplied by a value of the road frictional force F, and then subtracting a value of the braking torque T from the product.
According to another preferred embodiment of the present invention, the differential parameter M while the car is making a turn is obtained by using a cornering force F
s
acting on the wheel vertically to a direction of car's motion, instead of using the road frictional force F, from road frictional force information according to this cornering force F
s
and braking torque information according to the braking torque T.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a steering angle sensor for detecting the steering angle of the wheel for calculating an angle of side slip &bgr; as a deviation between an axis vertical to an axis of tire rotation and the direction in which the car is moving, and the cornering force F
s
is calculated from this angle of side slip &bgr;.
According to a second aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; a differential parameter calculating means for calculating a differential parameter M according to the road frictional force information and the braking torque information from the first sensors; and a brake fluid pressure controlling means for controlling brake fluid pressure of the braking equipment by using the differential parameter M and a first threshold according to a peak value of the differential parameter M. The ABS apparatus further comprises an arbitrary number of seconded sensors capable of obtaining gravitational acceleration information according to gravitational acceleration G acting on the car; and a gravitational acceleration change rate calculating means for calculating a gradient of locus given by the gravitational acceleration information from the second sensors. Road conditions are judged based on the gradient of the locus of gravitational acceleration information calculated by the gravitational acceleration change rate calculating means.
According to a preferred embodiment of the present invention, the brake fluid pressure controlling means starts and then stops a pressure reducing operation when the differential parameter M calculated by the differential parameter calculating means reaches a first threshold or a second threshold having an absolute value slightly smaller than that of the first threshold while the braking equipment is in operation.
According to another preferred embodiment of the present invention, the ABS apparatus further comprises a first threshold varying means for varying the first threshold according to the gradient of the locus of gravitational acceleration information calculated by the acceleration change rate calculating means.
According to a third aspect of the present invention, an ABS apparatus comprises an arbitrary number of first sensors capable of obtaining road frictional force information according to road frictional force F acting between a wheel of a car and a road on which the car is moving, and braking torque information according to braking torque T acting between the wheel of the car and a braking equipment; a differential parameter calculating means for calcula
Bednarek Michael D.
Japan Electronics Industry Ltd.
Pezzlo Benjamin A
Schwartz Christopher P.
Shaw Pittman LLP
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