Transmission belt and belt-speed-change device

A power transmission belt provided with a tension member extending in a lengthwise direction of a belt, a tension member-supporting layer in contact with at least a part of the tension member, a tension rubber layer formed on one surface of the tension member-supporting layer, and a compression rubber layer formed on the other surface of the tension member-supporting layer, the belt having a plurality of cog portions formed on an inner circumferential surface of the compression rubber layer along the lengthwise direction of the belt at a prescribed interval, and the belt frictionally engaging with a pulley on a side surface of the compression rubber layer,

• wherein the tension member is formed of an aramid fiber,
• the compression rubber layer is formed of a vulcanized rubber composition, the vulcanized rubber composition comprising:
• a rubber component,
• aramid short fibers in a proportion of from 20 to 30 parts by mass per 100 parts by mass of the rubber component, and
• carbon black,
• the aramid short fibers are embedded in the vulcanized rubber composition and oriented in a width direction of the belt,
• the power transmission belt has a strain of from 0.5 to 0.8% when compressed under a stress of 2.0 N/mm2 in the width direction,
• the power transmission belt has a strain of from 0.35 to 0.7% when pulled under a load of 2 kN in the lengthwise direction, and
• wherein the vulcanized rubber composition is characterized by a bending stress when a strain in a thickness direction reached 10%, of from 3.5 to 6.0 MPa, when performing press vulcanization at a temperature of 160° C. under a pressure of 2.0 MPa for 20 minutes.