1976-02-01

Frequency Response of Tires-Slip Angle and Lateral Force 760030

With theoretical studies as well as with practical tests on the subject of driving dynamics, frequency response of tires has to be taken into consideration, as it has been proved that steady state and transient tire properties are quite different from each other. Thus, for example, with sinusoidal slip angle input the ascertainment of a clear dependence of the lateral force on the slip angle is no longer possible.The rates of acceleration of slip angle and longitudinal slip, provoking transient behaviour, are so small that steady state measurements can be taken in exceptional cases only.On the Porsche tire testing rig, rolling wheels were electrohydraulically swivelled around their vertical axis. Frequency responses, ascertained by means of this sinusoidal slip angle input α = αosin ωt, will be explained in detail in the present paper.Transient lateral tire properties are shown in a wide range of frequency and speed. Different methods of plotting the results are explained.The relevant tendencies could easily be illustrated on logarithmically divided frequency and speed ordinates. Essential results: The lateral force amplitudes decrease and the phase angles increase as a function of the increase of frequency or the decrease of speed. With high speeds, the dynamic lateral force amplitudes So are bigger than the corresponding steady state values Sst.When relating both values to each other, the amplitude response So/Sst becomes sufficiently independent from the slip angle amplitude αo. Within the measuring range, the phase angle may also be considered as independent from αo.Examinations of the influence of path frequency revealed that it may well serve to unify the formation of the phase angle but that it does not affect the amplitude response. Some efforts are made in order to check the influence of parameters as frequency, speed, slip angle amplitude path frequency, weight of tire protector, profile height, tire pressure, wheel load, and tire construction

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