Fluid-pressure and analogous brake systems – Pipeless valves
Patent
1990-06-05
1993-02-23
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Pipeless valves
303103, 303111, 36442602, B60T 882
Patent
active
051884321
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of regulating the braking pressure in an antilock vehicle brake system in which the rotational behaviour of a braked wheel is measured and in dependence upon its slip and/or its angular retardation on exceeding at least one predetermined threshold value the braking pressure is normally lowered and later then increased again.
In antilock vehicle brake systems the rotation of the individual wheels of the vehicle is continuously monitored and in particular the slip of the braked wheels and their deceleration determined to detect a locking tendency of the wheel and prevent the locking. As soon as the wheel slip or the deceleration indicates a tendency to lock, which is determined by specific predetermined threshold values of slip and/or deceleration being exceeded, a further rise in the pressure in the brake of the affected wheel is stopped or the braking pressure diminished.
In particular, in the motor vehicle the wheel velocities of the driven wheels are measured and by differentiation of said velocity the wheel acceleration or deceleration is determined in each case for a single wheel. With the aid of the rotational velocity measured a so-called vehicle reference velocity is formed. If the rotational velocity of a wheel differs greatly from the reference velocity (so-called negative slip) or if the wheel reaches angular decelerations which are appreciably greater than the maximum physically possible vehicle deceleration (i.e. the deceleration which can be obtained with optimum braking, optimum tires and favourable road surface), the braking pressure at the affected wheel is decreased (usually by opening a magnetic valve) until the wheel again undergoes an acceleration lying above a predetermined threshold value.
The invention proceeds from this prior art. The underlying principles of the structure and function of antilock vehicle brake systems may be presumed known and are described for example in "BOSCH TECHNISCHE BERICHTE", vol. 7, 1980, No. 2, p. 65 to 94. In FIG. 20 therein an antilock system is described in which the rotational velocity of a wheel is measured. The pressure reduction does not start when an angular deceleration threshold is exceeded but only when the angular velocity of the wheel has decreased by a predetermined amount. This is an individual wheel control.
It is also known to connect the control passages of two wheels together, see DE 27 57 911 A1, where under critical driving conditions switchover takes place from an individual wheel control to a "select low" mode common to two wheels.
The antilock control of the braking pressure is concerned primarily with causing the peripheral velocity of the braked wheels to run as far as possible in the optimum range of the known adhesion coefficient/slip curve through all control cycles of a braking.
It has already been recognized in the prior art that for optimum regulation of the braking pressure adaptation of the threshold value to various conditions of the road surface/wheel system is necessary. Thus, for example, in DE-OS 3,345,729 account is taken of the fact that under certain conditions braked wheels may exhibit a rotational behaviour indicating pronounced angular deceleration although the wheel is still in a well brakable state. Such rotational or angular decelerations may occur in particular due to axle oscillations and simulate unstable running of the wheel and therefore initiate undesirable control operations, i.e. an undesired diminishing of the braking pressure. For this reason, in the prior art to suppress such undesired control operations the threshold value decisive for initiating the control is varied after a first control cycle in dependence upon the run-up acceleration of the controlled wheel.
Decisive for the shortest braking distance achievable on braking whilst maintaining steering stability of the vehicle is the adhesion coefficient .mu. between the road surface and the tire of the braked wheel. For this reason, the adhesion coefficient is also frequently referred to in the literature as "b
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Kampemann Wolfgang
Schmitt Hubert
Lucas Industries Public Limited Company
Oberleitner Robert J.
Young Lee W.
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