Evaluation of high-contact-ratio spur gears with profile modification
Scoring tests, surface fatigue tests, and single-tooth bending fatigue tests were conducted with four sets of spur gears of standard design and three sets of spur gears of the new tooth form (NTF) design. Scoring tests were conducted in a gear test rig at a speed of 10,000 rpm using a synthetic polyester C5, C6, C7 substituted pentaerythritol oil. Surface fatigue tests were conducted in the same rig at a speed of 10,000 rpm and Hertz stresses of 173 x 10 to the 7th power and 143 x 10 to the 7th power Pa (250,000 and 214,000 psi). Single tooth bending fatigue tests were conducted on both the standard and NTF gears at an initial load that produced a 10.35 x 10 to the eight power Pa (150,000-psi) bending stress. The gears were load cycled to failure or for 3 x 10 to the 6th power cycles, whichever occurred first. The load was increased after test until failure occurred at 3 x 10 to the 6th power cycles or less. Both the standard and NTF gears scored at a gear bulk temperature of approximately 409 K (277 F). At this temperature the load on the NTF gears was 22 percent less than the load on the standard gears. The scoring failure was a function of gear bulk temperature, where for a given lubricant the temperature is a function of gear design, operating load, and speed.