Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1992-12-10
1994-03-08
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
188181R, 303103, 303 91, 180169, B60T 858, B61C 1508
Patent
active
052921859
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a circuit arrangement for an anti-locking braking system for motor vehicles.
A known circuit arrangement (FR-A 2,250,098) of such a type relates to an anti-lock braking system for motor vehicles. Inter alia, it has an image correlator in which beams emitted from a light source are thrown onto the road and the reflected beams pass via a diffraction grating to two photo-electric receivers. When the vehicle is moving, the output signals of these receivers have a frequency component which is evaluated. At a vehicle speed which would lead to locking of the wheels and hence to the vehicle skidding in the event of sudden braking, the evaluation leads to the brakes of the vehicle being operated automatically and, in addition, to a suitable warning advice for the driver optionally being activated.
In contrast, normal anti-lock braking systems identify the start of the locking of a wheel in that the rotation speeds of the various wheels differ from one another in a typical manner. However, a difficulty with such a circuit arrangement is that it must also be able to identify that all the wheels are locked simultaneously when the vehicle is not yet stationary, that is to say when it is skidding over the ground beneath it with the wheels locked.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved anti-locking system for a vehicle that automatically senses the vehicle skidding when all wheels of the vehicle are locked.
This object is achieved by a circuit arrangement for an anti-lock braking system for motor vehicles, which has:
electronic wheel sensors which monitor the rotation of the wheels of the motor vehicle during braking;
a control unit which evaluates the signals from the wheel sensors an which acts on the wheels to prevent locking of the wheels;
a clearance sensor, which is fitted close to or on the vehicle floor and is directed toward the road surface, and which has a radiation transmitter and a radiation receiver;
a memory unit which briefly stores the signals received from the clearance sensor;
an evaluation unit, by means of which the stored signals of the clearance sensor are checked for changes which indicate a movement of the vehicle;
a second clearance sensor located close to or on the vehicle floor, and directed toward the road surface, such that it receives the signals reflected from the road surface at the point at which the first clearance sensor has previously received the reflected signals for a straight-ahead movement of the motor vehicle;
at least one adjustable delay unit connected to the evaluation unit, and the signal which is received from the first clearance sensor and stored being compared by the evaluation unit, after the adjusted delay time, with the signal received from the second clearance sensor, and, if the compared signals correspond, a control signal being transmitted to the control unit, which signal indicates that the motor vehicle is skidding.
Advantageous developments of the present invention are as follows. The clearance sensor has at least one ultrasound transmitter which ensonifies the road surface at a constant frequency. This makes it possible, at a particularly low cost, to estimate the speed at which the vehicle is skidding when its wheels are locked.
At least the evaluation unit and the memory unit are contained in a computer. This makes it possible to estimate, at low cost, considerably more accurately the speed at which the vehicle is skidding in a direction in which the two ground clearance sensors are arranged one behind the other on the vehicle floor.
The ground clearance sensor/the ground clearance sensors are sensors which receive ultrasound. This makes it possible to produce and the operate the arrangement at a particularly low cost.
At least a single ultrasound transmitter which ensonifies the road is/are fitted close to the ultrasound sensor/sensors. This makes it possible to use ultrasound sources which can be operated particularly reliably as well as those ultrasou
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patent: 4767164 (1988-08-01), Yeung
patent: 4965729 (1990-10-01), Hafner
patent: 5176431 (1993-01-01), Strehle
"Doppler radar skid control device enhances auto safety" by Y. Kaneko et al., Journal of Electronic Engineering, No. 133, Jan. 1978, pp. 54-57.
Butler Douglas C.
Siemens Aktiengesellschaft
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