Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1990-01-22
1991-07-23
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
188181C, 303100, 303105, 303110, B60T 866, B60T 832
Patent
active
050337998
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of controlling the brake pressure in an antilock vehicle brake system in which the rotational velocities of the vehicle wheels are measured and in dependence upon the retardation and/or the slip of a wheel on exceeding retardation or slip threshold values the brake pressure at said wheel is modulated, a reference velocity being formed in dependence upon the rotational velocity of the fastest rotating wheel.
In the technology of antilock brakes (ALB) it is known to carry out the brake control with the aid of a so-called vehicle reference velocity, often simply referred to as reference velocity, cf. in this connection in particular BOSCH TECHNISCHE BERICHTE, Vol. 7, 1980, No. 2, p. 81, corresponding to Bosch Technological Reports, English special edition, February 1982, ISSN 0006-798 X.
It is known to the expert in antilock technology that the so-called vehicle reference velocity, which should be as close as possible to the velocity, not directly measurable, of the vehicle, is used to determine the slip, i.e. the instantaneous peripheral velocity of a wheel is compared with the vehicle reference velocity and the difference gives the slip of the wheel which to obtain as short as possible a braking distance with simultaneous steerability of the vehicle is to be in the optimum range of the known coefficient of friction/slip curve.
As likewise known to the expert, the vehicle reference velocity is determined with the aid of the rotational velocities of the fastest rotating wheel of the vehicle. A frequent provision is the division of the four wheels of a vehicle into two groups of diagonally controlled wheels and the control of the two wheel groups separately, i.e. of the two diagonally arranged wheels the rotational velocity of the fastest rotating wheel is used to form the vehicle reference velocity.
Such a division into two wheel groups has the advantage that in the event of disturbances in the formation of a vehicle reference velocity an exact determination of the slip of the wheels is possible at least at the other wheels, i.e. those belonging to the other vehicle diagonal.
The use of the fastest wheel of the vehicle (or of the wheel of the vehicle) has of course the advantage that the vehicle reference velocity is frequently "supported". The term "supported" means that the vehicle reference velocity is frequently, i.e. at short intervals of time, readapted to the instantaneous vehicle situation by renewed measurement and evaluation.
However, this prior art has disadvantages in certain driving situations.
In particular, when braking in curves, especially also in emergency avoidance manoeuvres, the front wheel of the vehicle on the outside of the curve describes a greater radius than the other wheels and thus also generates the highest velocity. Thus, in accordance with the above observations the vehicle reference velocity is formed with this wheel. If braking is effected in such a situation the outer front wheel in the curve under road conditions with good coefficient of friction to obtain a short braking distance should however in this case as well reach as quickly as possible and continuously a slip which lies in the optimum range of the friction coefficient-slip graph. This optimum range of the friction coefficient-slip graph when braking in a curve lies at higher slip values than when braking in a straight line (see the above literature citation, page 68, FIG. 5). The wheel should also remain as far as possible without interruption in this range during the entire braking. Only then will a short braking distance be achieved with simultaneous steerability of the vehicle.
If however the fastest rotating wheel is used to form the vehicle reference velocity, i.e. in the situation described here the outer front wheel in the curve, and the slip calculation is related to said vehicle reference velocity, then because of the relatively high vehicle reference velocity, obtained moreover with a slight time delay, a relatively large slip is calculated for said wheel and it rapidly e
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Butler Douglas C.
Lucas Industries Public Limited Company
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