Abstract
In order to obtain the high tooth surface strength, various kinds of methods were tested using case hardened spur gears. The test results show that the suitable tip relief or tip&root relief following the load on the gear tooth to obtain the high tooth surface strength is necessary. The hobbed gear have very good strength and case hardening in a vacuum also showed high tooth surface strength than the usual case hardened gears, but the differences of the effective case depth affect little on the tooth surface strength. The barrel polished after ground and MoS_2 coated on the ground gears showed very good tooth surface strength. The test results show that the gears obtained here have about twice as much as power transmitting ability than the ISO proposal.
