Load Distribution in Timing Belts

A theory is presented for determining the distribution of the belt tension and the tooth load in timing belts. It appears that the distribution of both loads is of exponential character and one important parameter is the ratio between the spring constant of the tooth and the spring constant of the cord (a nondimensional number). Friction between the belt and the top of the pulley is also considered. This mostly influences the tooth load distribution. A criterion is presented for maximum tension ratio with respect to correct tooth action. Two belts are examined experimentally (steel cord-urethane and glass fiber cord-neoprene rubber). The spring constant of the tooth is determined both experimentally (a test procedure is presented) and theoretically (using the finite element method) and the agreement is good. The distribution of the belt tension in timing belt drives has been measured. The agreement between theory and experiment for the belts examined is satisfactory. Some discrepancies were observed. These will be the subject for further research.