Method and device for controlling slip and/or for determining th

Details Method and device for controlling slip and/or for determining th Method and device for controlling slip and/or for determining th

1997-06-16

1999-06-15

Felber, Joseph L.

Measuring and testing

Tire, tread or roadway

Tire inflation testing installation

731462, B60C 2304

Patent

active

059132400

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a method for making possible greatest possible accelerations via frictional engagement and a method for determining the longitudinal force acting on a tire or the tire spring travel or the footprint length or the load/pressure ratio and a device for determining the longitudinal force acting on a tire or the tire spring travel or the footprint length or the load/pressure ratio during rotation and a vehicle tire that is suitable for cooperation with the aforementioned device and/or for the aforementioned method.
A vehicle wheel in the context of this application is to be understood as a combination of all components which, with the exception of small load-depending deformations, are torsion-proof connected to one another and are designed for rotation. A wheel thus includes especially the tire, the wheel rim with wheel flange and wheel rim bowl, the valve, the hub, possibly sealing and/or securing rings attached thereto, brake disks, anti-lock magnet wheels and optionally drive shafts.
The invention is intended to increase the safety level of motor vehicles on wheels that are provided with tires, especially pneumatic tires, that, at least in the longitudinal directions, in general also in the transverse direction (one exception is the famous Metro in Paris provided with pneumatic tires), can transmit forces onto the road etc. only by frictional engagement. In most operational states the maximum possible frictional engagement is not even used; however, wherever it is necessary to react to unpredictable events, for example, a vehicle ahead that has spun out of control or a child running onto the street, so as to prevent dangerous situations, the attainability of great accelerations is required, especially with negative sign, i.e., great braking forces.
It is known that the value of greatest possible acceleration depends substantially on the coefficient of friction between the tires and the street. It is furthermore known, that this coefficient of friction is affected by the paring of the material street/tire, mostly asphalt/rubber mixture, the air pressure, the footprint length, and also the tire tread profile and the weather conditions. Furthermore, it is known that the coefficient of friction is a function of slip. Slip is to be understood as the difference between circumferential velocity of the tire minus steering knuckle velocity, divided by the steering knuckle velocity.
FIG. 1 shows for the conventional frictional material pairing for typical boundary conditions a curve of the coefficient of friction .mu..sub.longitudinal as a function of slip, in the following referred to as slip curve. The maximum longitudinal coefficient of friction is reached at a slip of approximately 10%. When the slip is increased further, which could be achieved during braking by increasing the braking moment, the coefficient of friction, together with the effective longitudinal force, would not increase further but, to the contrary, would decrease. This not only would result in the problem that the braking deceleration would decrease instantly, but would also lead to, when maintaining the too high braking moment, the wheel rotation frequency and thus the circumferential velocity of the tire would be reduced quickly to zero (the quicker, the smaller the moment of inertia of the tire--and it is relatively small in comparison to the vehicle mass). The operational state in which the wheel no longer rotates despite still present steering knuckle velocity, is called "locking". The slip is then -100%.
FIG. 2 shows in a solid line the slip curve for the same tire on cold ice (more unfavorable for warmer ice), and, as a comparison, in a thin dashed line the slip curve of FIG. 1 is shown again. The value .mu..sub.max is not only substantially lower but also occurs at smaller slip.
The runaway rotational deceleration of the tire occurring during vehicle deceleration, already at slightly increased braking moment, enhances the drawback of the initially only somewhat too great braking slip

REFERENCES:
patent: 4815004 (1989-03-01), Beebe

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