Page 99 - Gear Technology Solutions

There is no influence from one section to the other two sections. Due to the
integer ratio, the three sections develop independently from each other and
stay after break-in basically in a permanent condition.

Because the break-in degraded the quality of the gearset performance, it is
recommended to superfinish ground gearsets with integer ratios. Superfinish-
ing will prevent a further break-in, which in this case is an advantage because
it will preserve the initial motion transmission quality after grinding (see Fig-
ure 6).

7.4 Servicing a Transmission with Integer Ratio

If one of the two gears is removed during servicing the transmission, then it is
important to mark a tooth of the gear and the pinion slot it rolls with. If that is
not done, and the gears are assembled in a random orientation, then a much
bigger problem occurs. At the time of servicing, the tooth surfaces had already
been broken-in and a second attempted break-in with different tooth and slot
combinations will fail because the surfaces are too smooth and the hydrody-
namic oil film separates the flank surfaces. However, the larger motion error in
higher load conditions can cause the flank surfaces to break through the oil
film and damage the flank surfaces. In many known cases, the noise level of a
randomly assembled, already broken-in gearset with integer ratio increased.
This would often lead to the false concern that pre-loads had been wrongly ad-
justed or that the bearings were contaminated during the service call.

7.5 The Break-In Procedure

Break-In is an abrasive action which changes the micro-geometry on the flank
surfaces. A controlled break-in begins with light load and moderate RPM. Re-
versing the hand of rotation is recommended after only 20 minutes of opera-
tion.

Figure 8 shows the recommended break-in cycle for Super Reduction Hy-
poids. The surface in areas which cause a momentary acceleration impulse
will be abrasively altered more than areas without acceleration. Areas which
cause a momentary deceleration will show little or no surface alteration.

The surface action is a combination of removing sharp peaks and then super-
finish them with a mix of abrasive removal and a plastic deformation. This ex-
plains that broken-in gearsets have a polished appearance on the active areas
of the flank surfaces.

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