BELT-TYPE CONTINUOUSLY VARIABLE TRANSMISSION

PROBLEM TO BE SOLVED: To provide a belt-type continuously variable transmission which keeps a higher coefficient of friction and wear resistance than ever before for a long term and can withstand long-term use.SOLUTION: A Zn-diffusion layer with a discharge crater diameter of 5 μm or less and surface roughness of Ra 0.2 or less is provided at least on a front layer of a contact face with a pulley element by discharge surface treatment. By making the discharge crater diameter of 5 μm or less, a sufficient amount of the diffusion layer to improve wear resistance of the pulley can be formed on the pulley surface uniformly and over a wide range even if the surface roughness is Ra 0.2 or less. Thus, a true contact area of the contact face enlarges and a contact pressure can be reduced, thereby alleviating reduction in the true contact area due to peel and wear on an element side. In addition, since drop in compressive residual stress can be suppressed and the wear resistance of the pulley itself can be improved, the reduction in the true contact area on a pulley side can be alleviated. A high coefficient of friction and the wear resistance on the contact face can thus be kept for a long term, and long-term use can be supported.