Abstract
Tire radiation noise is one of the largest sources in road traffic noise problem. However, basic understandings of tire noise radiation mechanism is not sufficient to design tires that improves noise radiation without sacrificing other functions such as traction, durability, low rolling resistance, ride comfort. One of the reasons of this is due to the fact that tire radiation noise is a high-frequency phenomenon that is hard to solve by conventional mode analysis approaches.
In the first part, excitation mechanism at the tire-road contact surface was investigated. Laser scanner and image processing were used in two ways. One is tread surface macro deformation shape measurement for modelling tread-road contact incidence velocity. The other is to measure the dent shape on treads around points of contact with shingles. Then, measurement of high-frequency vibration propagation on a tread was conducted. Based on this information, finite element models were developed to investigate the effects of tire structural elements on vibration wave propagation. The simplest model is a flat composite panel with such layers of tread rubber, steel belt, carcass and cap rubber. Another model representing the real tire shape was built using material properties obtained by shaker tests.
The results proved that shingle tops act as forced velocity excitation sources on to a tread like rain drops on roof. Effects of tread-road contact length and tread bending stiffness on this excitation were clarified. Air pumping motion of tread grooves was estimated quantitatively as two different actions, i.e.; one is the groove mouth opening and closing by sharp tread bending deformation near the leading and trailing edges of contact patch; and the other is shrinkage of groove height by the contact pressure change along the path. Propagation of the tread bending wave was measured and its group velocity and decay rate were obtained. The flat composite panel FEM model showed that vibration propagation velocity is determined primarily by steel belt and groove arrangement and decay rate is by tread rubber. Vibration propagation observed in the three dimensional single layered FEM model suggested the existence of in-plane waves as well as out-of-plane waves.
Through these studies, quantitative models of excitation and propagation of high-frequency vibration on tire tread were developed including such factors as tire deformation shape just before and after contacting road surface, impact of each shingles on tread, influences of each layer of composite tread structure. Usage of three-dimensional laser scanner and FEM wave propagation simulations were the key factors that enabled these modelling. As a result, understanding of high-frequency tire radiation noise generating mechanism has been improved.
KEYWORDS – Noise, Vibration, Tire, Simulation, FEM