Fluid-pressure and analogous brake systems – Pipeless valves
Patent
1992-12-11
1994-06-21
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Pipeless valves
303100, 303110, 36442602, 180197, B60T 832
Patent
active
053223551
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an anti-skid brake control system for a motor vehicle having forward and rearward sets of vehicle wheels, at least one of which is driven. The anti-skid brake control system includes speed sensors associated with the vehicle wheels; an evaluation circuit responsive to the wheel speed sensors for producing brake pressure control signals; and brake pressure control means for controlling the brake pressure applied to the vehicle wheels in response to the control signals.
At a low friction coefficient, and this applies especially to a rear wheel driven vehicle, there is a situation in which, during the control of a pressure level corresponding to the locking limit of the front wheels, the momentary balance at the rear axle between braking torque and driving torque--especially at a high idle speed during cold operation--results in a positive driving torque. A consequence thereof is that the vehicle does not come to complete stop despite a locking of the front wheels. A stopping of the vehicle is only possible when the brake pressure is increased to a value which exceeds the motor driving torque. This requires in some cases significant brake pressures and hence high pedal forces.
This situation can be intensified with the combination of an anti-skid brake control system based on the feedback principle and a vacuum brake power booster. When the energy consumed by the pressure modulation is not sufficiently replaced and when the throttle is partially open, the level control point of the booster continuously decreases. In this case the foot pressure required for reaching a sufficient pressure level to surpass the driving torque increases to values which cannot be reached in borderline cases.
The above described problems can result in a situation in which a vehicle--especially with rear drive--cannot be stopped on a slippery road even when great pedal forces are applied unless the driver disengages the clutch or sets the shift lever of an automatic transmission to "neutral". However, especially in case of an automatic transmission, such a reaction cannot be expected by a driver in a "stress situation".
SUMMARY OF THE INVENTION
It is an object of the invention to configure an anti-skid brake control system such that the above described problems are avoided.
This object, as well as other objects which will become apparent from the description that follows, are achieved, in accordance with the present invention, by providing the anti-skid brake control system with a device for determining whether the speed decrease of a non-driven wheel falls below a prescribed small value within prescribed periods of time during activation of the brake pressure control, and a device responsive to the determining device for effecting at least one of the following:
(1) disabling the anti-skid brake control function of at least the non-driven wheel set, and
(2) reducing the driving torque on the driven wheel set.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention and to the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING The only figure illustrates an embodiment
of an anti-skid brake control system in accordance with the invention represented as a block diagram.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The anti-skid brake control system includes shown in the figure four speed sensors 1 to 4 for the wheel speeds which are assigned to the front wheels (1 and 2) and the driven rear wheels (3 and 4). The signals thereof are supplied to an evaluation circuit as it is commonly known. From the supplied speed sensor signals this circuit generates brake pressure control signals for the brake pressure control devices 6 to 9, represented as solenoid valves, so as to vary the brake pressure at the front wheels (valves 6 and 7) and the rear wheels (valves 8 and 9).
The evaluation circuit 5 includes a block 5a here the reference speed V.sub.Ref (a speed curve approximated
REFERENCES:
patent: Re31383 (1983-09-01), Leiber et al.
patent: 3702206 (1972-11-01), Sweet
patent: 3740103 (1973-06-01), Sweet et al.
patent: 4491919 (1985-01-01), Leiber
patent: 4499543 (1985-02-01), Matsuda
patent: 4626040 (1986-12-01), Ogino
patent: 4848851 (1989-07-01), Kuraoka et al.
Systeme antiblocage avec fonctions elargies No. 7, Oct. 1984 pp. 110-116.
Oberleitner Robert J.
Poon Peter M.
Robert & Bosch GmbH
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