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The Impact of Surface Condition and Lubricant on Gear Tooth Friction

Gear friction, with specific emphasis on the teeth, can be impacted by the surface condition and lubricant used. For the full resource, fill out the form below the abstract.

By: Suren Rao and Aaron Isaacson, Gear Research Institute and Gary Sroka and Lane Winkelmann, REM Surface Engineering

Technical Papers and White Papers

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 19 m/sec) to 10,000 rpm (pitch-line velocity of 47 m/sec) are evaluated.

Input torque measurements, as measured by the precision torque transducer, on ground test gears operating in MIL-23699 lubricant are used as a base line.  The increase or decrease in the input torque to the four-square loop is a measure of the change in friction losses at the test gear mesh due to changing surface condition, tooth load and or lubricant.  Based on the collected data, a qualitative analysis of the effect of gear tooth surface condition on frictional losses is presented.  Further, the surface characteristics of the tooth flanks of the ground, superfinished and coated gears are also described.  Plans for future work, to obtain a quantitative measure of the effective coefficient of friction at the tooth surface, are also propose

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