Growth in Clearance between Square-cross-sectioned Shaft and Square-holed Lever under Dynamic Loads

Abstract

A fit structure composed of a square-cross-section shaft and a square-holed lever is often used as a torque-transmitting mechanism. This structure can be degraded, however, if it is subjected to repeated dynamic loads. If the clearance between the shaft and the lever grows too wide, the structure may not be able to transmit the torque smoothly. We studied this growth in the clearance for a fit structure used in electrical machinery. We found that the initial clearance due to the difference in size between the shaft and lever causes plastic deformation to begin in the early stage of loading. This enlarges clearance at the point where the shaft and lever make contact. Also, under dynamic loading, the increase in the clearance increases the service load on the fit structure. We estimated the growth in the clearance by comparing the magnitudes of the resistance of the structure and of the service load for the same clearance.