Brake slippage control

Details Brake slippage control Brake slippage control

1990-04-16

1992-08-04

Black, Thomas G.

Boots, shoes, and leggings

180197, 303 95, B60K 3100

Patent

active

051365090

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a brake slippage control wherein the deviation of a signal corresponding to the wheel speed from prescribed portion of a reference speed approximated to the vehicle speed is determined and used to change the brake pressure.
In known slippage controls for vehicles, a reference value is recovered from the speeds of one or several vehicle wheels and approximated to the curve of the vehicle speed. One or several percentages of this reference value are formed and compared to the speed signal of the wheel. When the wheel speed signal falls below or exceeds these percentages (e.g. 95% and 80%), which serve as thresholds, control signals are derived and a brake pressure control unit is activated for pressure variation.


SUMMARY OF THE INVENTION

According to the invention, the deviation .DELTA..lambda., is supplied to a control amplifier which is provided with a proportional-differential conversion property having a resettable integral portion. The output signal .+-.U of the control amplifier is used for actuating a brake pressure control unit comprising hydraulic valves. The magnitude and sign of the output signal determine the time during which pressure is built up, reduced, or maintained constant. The control is temporarily interrupted for a short period in which the reference speed and the increase thereof are actualized.
During the controlled braking of a vehicle wheel in regular operation, a brake slippage value is selected which corresponds to the maximum adhesion coefficient of the wheel in longitudinal direction. To improve control over the vehicle, it is possible to apply a selected underbraking to the wheel via an externally triggered operator action. The control generates very small brake pressure amplitudes which is advantageous with regard to comfort and energy consumption. Since the evaluation carried out is slippage-defined, the control has an improved robustness against interferences as compared to those controls operating in dependency upon the wheel acceleration. The clearly arranged design, the small memory capacity which is required and the small number of parameters are of interest with respect to realizing a microcomputer.


BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a control circuit;
FIG. 2 shows the characteristics of the control amplifier;
FIG. 3 shows the relationship of the various speeds to time;
FIG. 4 is a possible characteristic curve of the control output;
FIG. 5 shows the brake pressure as a function of wheel slippage.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 a wheel brake 1 affects the controlled system 2 including the systems wheel, tire and road. This controlled system 2 has the input values braking torque T.sub.B and vehicle speed V.sub.veh and the output value wheel speed v.sub.w. The measured wheel speed signal v.sub.w is supplied to a slippage calculator 3 to which a reference value v.sub.Ref from block 5 is also supplied. Further, this reference value v.sub.Ref is also supplied to a desired slippage calculator 4 which determines a desired slippage value .lambda.*, e.g. 5%. The desired slippage calculator 4 can be actuated via terminal 6 and switched over to another value (e.g. in a curve).
The slippage .lambda. which is formed in the slippage calculator 3 according to the relation deviation .DELTA..lambda. is supplied to a control amplifier 8. The latter essentially has proportional-differential transmission properties between the control deviation .DELTA..lambda. and its output value U, a resettable integral portion (i.e., the I-portion is reset for (U.sub.2 (K-1).gtoreq.T.sub.min), a dependency of its amplification upon the reference speed v.sub.Ref and logic scans which serve to apply various control rules depending upon the preceding sign of .DELTA..lambda. and d .DELTA..lambda./dt.
With the deviation ##EQU1## According to I-portion, which can be calculated from ##EQU2## The letter K is an index for the scanning interval. Further, the I-portion Umem is set to zero when the

REFERENCES:
patent: 3635530 (1972-01-01), Packer et al.
patent: 3838890 (1974-10-01), Wind
patent: 3857612 (1974-12-01), Bynum
patent: 4924395 (1990-05-01), Evans et al.
patent: 4947954 (1990-08-01), Fujita et al.
patent: 4971164 (1990-11-01), Fujita et al.
patent: 4985837 (1991-01-01), Togai et al.
patent: 5000280 (1991-03-01), Wazaki et al.

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