US Patent 7144345 Toothed belt transmission

A toothed belt transmission is provided in which a toothed belt is trained around drive and driven pulleys. Each toothed pulley has a circumferential periphery formed with a plurality of teeth. Adjacent teeth are assigned as a first tooth portion and a second tooth portion. Respective tooth portions have arcuate portions at corners defined between tooth edges and tooth surfaces. A line touching the arcuate portions of the first and second tooth portions is assigned as a common tangential line. A line passing over a starting point of the arcuate portion of the tooth edge of the first tooth is assigned as a first tangential line. An angle between the common tangential line and the first tangential line falls in a range between 6° and 14.4°.