Helically toothed belt power transmitting device

A helical toothed belt power-transmission device comprising:

• a helical toothed belt comprising:
• a back portion in which a tension member is embedded, and
• a plurality of tooth portions which are provided on one surface of the back portion at prescribed intervals along a belt longitudinal direction and each of which is inclined with respect to a belt width direction, surfaces of the tooth portions being formed of a tooth fabric;
• a drive pulley comprising drive pulley grooves meshing with the tooth portions and being configured to be rotatably driven by a drive source;
• and
• a driven pulley comprising driven pulley grooves meshing with the tooth portions,
• wherein the helical toothed belt has a belt width of 1 mm or more and 18 mm or less,
• wherein the tension member is a twisted cord comprising a high-strength glass fiber or a carbon fiber and having a diameter of 0.2 mm or more and 0.9 mm or less, and
• wherein a compression ratio of the tooth portions due to the drive pulley grooves and the driven pulley grooves, defined by the following formula, is 0% or more and 5% or less:
• Compression ratio=(tooth height−pulley groove depth)/tooth height×100.