Fluid-pressure and analogous brake systems – Speed-controlled – Pressure release control
Patent
1995-03-03
1997-07-08
Ballato, Josie
Fluid-pressure and analogous brake systems
Speed-controlled
Pressure release control
303149, B60T 832
Patent
active
056453272
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an antilock control system (ABS) in which measured wheel speeds are fed to an evaluation circuit which produces brake pressure control signals for increasing and decreasing brake pressure in stages having specific durations. In these known systems, it is possible that, given full application of the brakes for only a short time, the braking distance may in certain conditions be longer than in a vehicle without ABS.
SUMMARY OF THE INVENTION
The invention is based on an antilock control system for motor vehicles, in which the wheel speeds are measured by means of wheel speed sensors and are fed to an evaluation circuit. By means of the evaluation circuit, brake pressure control signals at least for increasing pressure and for decreasing pressure for a specific duration are then produced for the closed-loop/open-loop control of the wheel movement behavior. Moreover, brake pressure control signals are also usually output by the evaluation circuit in order to keep the brake pressure constant. These brake pressure control signals are fed to brake pressure control units for varying the brake pressure. The core of the invention consists in the fact that the duration at least of the first decrease in brake pressure is selected to be dependent on the vehicle speed at the start of braking.
The advantage of the invention consists in the fact that the braking distance is shortened for full braking starting from a relatively low speed. The invention therefore prevents lengthening of the braking distance in vehicles with ABS, in comparison with vehicles without ABS, given full braking starting from a relatively low speed.
In particular, there is provision according to the invention for the decrease in brake pressure to be influenced at the front wheels, but such influencing of the decrease in brake pressure is also possible at the rear wheels.
In an advantageous embodiment of the invention there is provision for the duration of at least the first decrease in brake pressure to be selected to be additionally dependent on the determined grip of the underlying surface.
During the first control cycle of the ABS, the utilization of the braking power is significantly less efficient than in the subsequent control cycles. This is because in the case of full application of the brakes, due to occurrence of slippages, the controller must cope with a highly non-steady-state process at the start of control and because the feedback necessary for optimization is only available in the following control cycles. If the entire process of full application of the brakes is relatively short, the first control cycle (or cycles) goes into strong braking, as a result of which the resulting braking distance may be longer than in the case of braking without ABS. This applies typically if full braking takes place at a relatively low starting speed on an underlying surface with good grip.
The invention tolerates the fact that the steerability may be reduced in the first control cycle (or cycles); the driving stability is however retained completely. The following estimation shows that, under the given circumstances, shortening the braking distance is more important for avoiding an accident than optimum steerability.
At an initial speed of 40 km/h and with a deceleration of 10 m/sec.sup.2, a time with reduced steerability of approximately 1 sec results; in this time, little can be achieved by means of a steering maneuver.
In particular, there is provision according to the invention for the duration of at least the first decrease in brake pressure which takes place within the first control cycle to be selected to be longer at higher vehicle speeds at the start of braking than at lower vehicle speeds at the start of braking.
In a simple embodiment of the invention, the duration has a fixed value if the speed of the vehicle is lower at the start of braking than a selectable first threshold value. If the speed of the vehicle is higher at the start of braking than the selectable first threshold value,
REFERENCES:
patent: 4027926 (1977-06-01), Arai et al.
patent: 4485445 (1984-11-01), Braschel
patent: 4693522 (1987-09-01), Wupper et al.
patent: 4933858 (1990-06-01), Matsuda
patent: 5109339 (1992-04-01), Watanabe et al.
patent: 5273350 (1993-12-01), Yagi et al.
Czinczel Armin
Isella Thomas
Steinke Leo
Ballato Josie
Robert & Bosch GmbH
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