This research is a fundamental study for improving the tooth surface durability by multiplex surface modification to reduce the size of gear transmission unit. The aim of this study is to clarify the improving mechanism of tooth surface durability, the surface failure mechanism, the design method for surface durability and the evaluation method of dynamic performance of gear.
The operating fatigue tests of gears and rollers, which were shot-peened after the case hardening, were performed using a power circulating gear test machine developed in 1997 and a conventional two cylinder test machine.
In the case of steel, the surface durability of shot-peened gear and roller was improved since the compressive residual stress was increased by the shot-peening and the crack initiation and propagation were restrained.
In the case of sintered powder metal, the surface durability was decreased by the shot-peening with the higher arc-height value since the pores in the material were crushed and the notch sensitivity factor was increased, while, the surface durability was increased by the shot-peening with the lower arc-height value since the pores were hardly crushed and the effects of work-hardening and compressive residual stress were achieved.
The dynamic performance of the gear was also investigated using the wavelet transform. The vibration and noise of the surface modified sintered gear were lower than those of the steel one.