Method of improving ABS control behavior

Details Method of improving ABS control behavior Method of improving ABS control behavior

1999-05-05

2001-03-13

Cuchlinski, Jr., William A. (Department: 3661)

Data processing: vehicles, navigation, and relative location

Vehicle control, guidance, operation, or indication

Indication or control of braking, acceleration, or deceleration

C701S070000, C701S071000, C701S074000, C303S122060, C303S182000, C303S189000, C180S197000

Reexamination Certificate

active

06202019

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of improving the control behavior of an anti-lock control system, wherein a vehicle reference speed that is used as a reference quantity to determine the wheel slip of the individual wheels is derived from the rotating behavior of the vehicle wheels, and criteria are obtained for identifying a cornering situation and the curve direction, wherein for identifying cornering the wheel slip values are filtered by way of a low-pass filter and the filtered values are compared.
It is already known in the art to extend the functions of an anti-lock control system by employing the system for improving the driving stability or deceleration stability in the curve. For this purpose, during cornering or during a partial deceleration, i.e., in a deceleration process in which the threshold of response to the anti-lock control system is not achieved, a stabilizing moment about the vertical axis of the vehicle is created by specifically delaying the brake pressure build-up on the wheels at the inner side of the curve compared to the brake pressure on the wheels on the outer side of the curve (‘Bremsanlage und Schlupf-Regelsystem der neuen 7-er Reihe von BMW’ (Brake System and Slip Control System of the new BMW No. 7 series); ATZ 97 (1995), pp. 8-15, and ‘Bremsanlage und Schlupf-Regelsysteme der neuen Baureihe 5 von BMW’ (Brake System and Slip Control Systems of the new BMW No. 5 series); ATZ 98 (1996), pp. 188-194. The information on the actual steering angle is derived—if no steering angle sensor is used—from the transverse acceleration which, in turn, is calculated from the wheel sensor signals.
DE 34 13 738 C2 discloses an anti-lock control system (ABS) provided with a system for identifying a cornering situation based on wheel slip measurement. To identify a cornering situation, the sum of slip values on the wheels at one vehicle side are summed up and compared to the slip values on the wheels at the other vehicle side, generating a cornering identification signal as soon as the difference of the summed-up slip values exceeds a predetermined limit value. Upon identification of a cornering situation, selective criteria, such as ‘select-low’ or ‘select high’ according to which the pressure variation in the individual brake pressure control channels of the said brake system is controlled, and limit values for rendering the said selective criteria effective, are varied. In this way, the control will be adjusted to the varying conditions during straight-forward driving and during cornering.
DE 21 19 590 A1 which has an older filing date teaches generating a cornering identification signal with the aid of a transverse acceleration meter, such as a mercury switch.
The calculation of the filtered wheel slip and the evaluation of this quantity to determine criteria for cornering are described in the patent application DE 195 22 634 A1 which is not prior published. The filtered wheel slip values are compared and evaluated for cornering identification according to the above publications. Cornering is identified when simultaneously the values of the filtered wheel slip on both front wheels exceed a predetermined maximum slip value and the filtered wheel slip of a rear wheel is in excess of an equally predetermined maximum slip value and the filtered wheel slip of the second rear wheel is below a determined minimum slip value.
When cornering is identified, switch-over to a special, i.e., cornering, control mode is effected according to patent application DE 195 22 632 A1 which is also not prior published.
An object of the present invention is to improve, in a method of the type referred to hereinabove, the ability of evaluating the measuring signals and, more particularly, the reliable identification of a cornering situation compared to straight travel.
SUMMARY OF THE INVENTION
It has been found that this object may be achieved by a method the special feature of which includes that a filter of first order is used as a low-pass filter to process the wheel slip values, the time constant of which filter is varied as a function of the acceleration of the respective wheel. Advantageously, the time constant T
i
of the filter, starting from a minimum value T
min
, is increased according to the relation
T
i
=T
min
+(
a
grenz
−a
i
)/k
1
with
i=
1 . . . 4
as soon as the acceleration ai of the respective wheel i drops below a predetermined limit value (in other words: exceeds a deceleration limit value).
The filtered wheel slip is a key signal of a control of this type. The safety of identifying the slip condition is greatly improved by increasing the time constant at greater wheel decelerations, i.e., at wheel accelerations below the predetermined limit value. The minimum value of the filter time constant is decisive at greater wheel accelerations.
In another preferred embodiment of the present invention, when programmed circuits are used, the filtered wheel slip values fws
i
are produced for each individual wheel according to the relation
fws
ineu
=fws
ialt
+(
v
REF
−v
i
−fws
ialt
)/
T
i
wherein ‘fws
neu
’ refers to the wheel slip value which was last determined in the working cycle, ‘fws
alt
’ refers to the filtered wheel slip value which was previously determined in the working cycle, ‘v
REF
’ refers to a vehicle reference speed, and ‘v
i
’ refers to the wheel speed and ‘T
i
’ to the variable time constant.
Further features, advantages and possible applications of the present invention can be taken from the following description making reference to the accompanying drawings.


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