Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1990-10-09
1993-03-23
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303 221, 303 241, B60T 858
Patent
active
051958082
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns systems and methods for braking of and traction for wheeled vehicles, and more particularly optimum braking and traction under any road or ground conditions.
The principles utilized in the present invention are to a certain extent described in Applicant's previous Norwegian patent application no. 88.1513, which hereby is incorporated by reference.
Traction is in the present context meant to be understood as the powered acceleration of a wheel, i.e. the opposite of braking.
The present invention has particularly been developed in connection with the need of ability to undertake braking, or possibly traction, while utilizing maximally the attainable friction coefficient between a wheel and a ground course, particularly with pneumatic tires and the surface of runways and roads. Said friction coefficient, usually designated .mu., depends on weather conditions, and may therefore vary considerably. As will be explained in more detail later in this specification, the friction coefficient .mu. also is strongly dependent on the so-called "slip" conditions of the wheel. A precise and fast adjustment to the optimum braking force value is of considerable benefit for example to a pilot in an airplane at departure and landing, because such an adjustment renders possible optimum braking and avoidance of skidding.
For a railway train also the acceleration phase is important, since optimum utilization of power and minimum wear of material is achieved by rapid adjustment of the optimum traction, so that unnecessary and damaging wheel skidding is avoided and the train reaches its cruising speed in the fastest possible manner.
Also for ordinary motor vehicles, i.e. cars, lorries, tractors etc., good automatic braking systems, i.e. non-blocking systems, are of interest for safety reasons. In particular cases, also an effective traction control may be advantageous, for example in sports-like driving and in driving outside roads in rugged terrain.
Braking systems have been developed previously, which systems seek to avoid blocking the wheels during a hard braking action, but it has turned out that these systems may give results which are not completely satisfactory, which fact has led to a few airplane accidents in the braking phase, which accidents might have been avoided. The problem is often that the existing systems do not really know the state of movement of the airplane, only whether the wheels are rotating or not.
Previously known braking systems for cars are also usually based upon sensing the rotational state of the wheels--if the wheel stops rotating, the braking power is cut. In some related systems, i.e. mainly systems for measuring friction, particularly between an airplane wheel and the runway, the friction force is measured for a wheel during braking, at a certain slip factor for the wheel. The slip factor gives an expression of the slip or the sliding between a rotating wheel and the ground. It is necessary that a wheel is subjected to slip in order that horizontal forces be transferred when the wheel is rolling. In this connection the slip factor S is defined as ##EQU1## in which n.sub.k is the number of revolutions of a freely rotating wheel in contact with the ground, and n.sub.b is the number of revolutions of the braked wheel.
In the formula above the slip factor is a number between 0 and 1, however said factor may also be expressed in percent, i.e. ##EQU2## and the slip factor will then be a number between 0 and 100. 100% slip thus means a locked, braked wheel (total panic braking), and 0% means no braking of the same wheel, i.e. a freely rotating wheel.
In airport runways it has become usual to make friction measurements with a slip factor between 15 and 17%. However, the friction coefficients or friction forces obtained in these measurements, will only be correct, i.e. the maximum possible values, for one particular type of ground conditions. It has turned out as a fact that the slip factor which provides maximum runway friction, will be lower un
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Muratori Alfred
Oberleitner Robert J.
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