Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1993-11-19
1995-04-18
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303103, 303106, 303111, 303DIG4, B60T 864, B60T 860, B60T 872
Patent
active
054072581
DESCRIPTION:
BRIEF SUMMARY
This application is a national phase filing of International Application No. PCT/EP92/00609.
BACKGROUND OF THE INVENTION
This invention relates to a circuit configuration for an automotive vehicle brake system with electronic anti-lock control. The circuit configuration includes circuits for individually controlling the braking pressure in the wheel brakes of the two wheels of one axle as a function of the rotational behavior of the wheels measured by wheel sensors. The circuit configuration also includes circuits for limiting the yawing moment due to braking pressure differences at the wheels of one axle, by maintaining the braking pressure differences below a permissible pressure difference being variable as a function of the friction value difference at the two wheels.
A similar circuit configuration has been disclosed by DE 39 25 828 A1 (German Patent Application). This patent application discloses an anti-lock control system with individual control of the braking pressure at the two wheels of one axle. In order to limit the yawing moment on road surfaces with very different friction values on the right and left sides, i.e., with .mu.-split conditions, the pressure difference is limited and, in doing so, the permissible pressure difference is determined as a function of the friction value difference and on the amount of the lower friction value. If this permissible pressure difference is exceeded, pressure will be reduced at the high-value wheel in consideration of the kinetic state of the low-value wheel. In order to determine the permissible pressure difference, in this known anti-lock control system, the pressure metered in by the driver will be measured on the right and left wheels and in either case the nominal pressure will be compared with the actual pressure. The friction value (i.e. friction coefficient) is assessed as a function of the braking pressure. If a predetermined pressure difference is exceeded, braking pressure will be reduced at the high-value wheel, namely at the higher-pressure wheel.
From the aforementioned German Patent Application and from DE 28 51 107 C2 (German Patent Application), it is also already known to perform the pressure reduction for the sake of limiting the yawing moment when, at the end of a control cycle, the low-value wheel again reaches the stable range.
The expenditure for individually measuring braking pressure at each wheel, and evaluating and monitoring the measured results, is significant.
SUMMARY OF THE INVENTION
The present invention pertains to developing a circuit configuration for an anti-lock control system which, on the one hand, ensures the maintenance of the driving stability of the vehicle by limiting the yawing moments--including in critical situations with a high friction value difference on the right and left sides--while simultaneously achieving an effective braking operation with a short stopping distance by utilizing the efficiency of the brakes as well as possible.
The circuit configuration of the present invention includes circuits: (1) which continuously detect a value from pressure reduction signals, this value representing the pressure difference at the two wheels of the one axle; (2) which, in the case of different friction values (i.e. a .mu.-split situation), vary the mean pressure build-up gradient at the high-value wheel--i.e., at the wheel of less pressure reduction--as a function of the pressure difference or rather on the value representing the pressure difference and on the vehicle deceleration; and (3) which, at the time of the appearance of the so-called peak yawing moment, namely shortly before the wheel running on the lower friction value will reenter the stable range, reduce the braking pressure at the high-value wheel by a value dependent (inter alia) on the vehicle deceleration and on the pressure difference.
According to the present invention, on a road surface with different friction values on the right and left vehicle sides, the braking pressure and the braking pressure difference are controlled, without pres
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patent: 5066074 (1991-11-01), Wupper
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Fachinger Georg
Giers Bernhard
Niepelt Mathias
Wieland Andreas
Woywod Juergen
Butler Douglas C.
ITT Automotive Europe GmbH
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