Frictional losses in gear boxes are of significant interest to gear box designers as these losses transform
into heat. The direct result is a reduction in the fuel efficiency of the vehicle involved. Further, in many
instances, this heat has to be absorbed and dissipated so that lubricant properties and gear box
performance are not significantly compromised. This effort is to measure and document the comparative
friction losses in a gear mesh due to gear tooth surface condition and lubricant. Three distinct surface
conditions are considered. They are ground, isotropic superfinished (REM ISF®) and tungsten
incorporated diamond-like carbon coating (W-DLC) which is a wear resistant coating. Two lubricants,
MIL-PRF-23699 (ISO VG 22) and Mobil SHC 626 (ISO VG 68) are considered.
The experimental effort is conducted on a high speed, power re-circulating (PC), gear test rig, which had
been specially instrumented with a precision torque transducer to measure input torque to the four-square
loop. The torque required to drive the loop is measured under various speeds and tooth loads within the
torque loop, with test gears with different surface conditions and with different lubricants. Two operating
torque levels within the four-square loop at speeds ranging from 4,000 rpm (pitch-line velocity of 1 9
m/sec) to 1 0,000 rpm (pitch-line velocity of 47 m/sec) are evaluated.

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