Synchronous belt and its driving pulley have non-conjugate tooth profiles. Because of non-conjugate motion and polygon effect, interference occurs during incomplete meshing, resulting in excessive wear and tear at tooth-root, which are the main forms of failure of synchronous belts. Tooth cracking also results from uneven stress distribution and/or increased maximal stress. In addition to discovering better materials to increase the strength of the belt's teeth, optimization of the geometry of tooth profiles of belt and pulley to decrease the maximum tooth-root stress and to reduce interference during meshing is critical in improving the carrying capacity and increasing the belt's life span. In the present study we proposed a new design of synchronous belt's and pulley's tooth profiles, modifying several key geometric parameters commonly used in synchronous belts' designs. Applying the conformal mapping function and the theory of plane elasticity we systemically investigated the distribution of stress and distortion at the belt's and pulley's teeth of varying geometric parameters and analyzed the interference during meshing using an approach to investigating tooth profiles of non-constant pitch diameter. Finite Element Analysis showed that with the same load the maximum principal stress valuesof belt teeth in complete meshing in our design (STSB) were 54.4% and 67.8% of that of HTD (by Uniroyal) and STPD (by Good Year) belts with an 8 mm pitch commonly used in automobiles, respectively. The uneven distribution of stress along the edge of tooth profile was reduced, and the interference during meshing minimized with our design. We then experimentally tested belts made of the same materials with the three designs manufactured by the same factory. The belts were tested in the enclosed type of testing machine for synchronous belt's fatigue-life, power = 6.5 kW and speed = 1500 r/min with test belt tension at 400 N. The fatigue lives of the belts (n=5 each group) were 988±36, 439±21 and 665±22 hours (mean ± SD) for STSB, HTD and STPD belts (p<0.0001), respectively, demonstrating the superiority of our design. We anticipate that the new design will have wide applications not limited to the automobile industry.
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