Special Noise Problems in Automotive Timing Belts

During the development of an automotive engine with timing belt usually problems with timing belt noise occur. This paper describes the solution of two different noise problems excited by the timing belt. These problems were mainly sound quality issues and required dedicated analysis methods such as listening studies or time domain analysis in defined frequency bands. First a short overview to the theory of belt noise is given.

The first problem was caused by torsional vibrations of a belt span which forces the balls of the bearing of an idler to move through their clearance. This leads to a high frequency noise (rattle). The detailed analysis of that problem leads to a V-shaped idler with greater diameter. The second problem was caused by a natural frequency of an idler which was excited by belt span vibrations (warble). An idler with a small add on ring, a shift of natural frequency and a modified sprocket profile gives the solution for that concern. In addition to the problem solutions the influence of pretensioning procedure on timing belt noise will be described.