I am involved in analysing a differential gearset. One design criteria is full torque reversal cycles caused by the driver "rocking" the vehicle out of some ugly terrain. Although the driver is in the full revese torque mode, the differential is not exactly in the same mode; the gear teeth are loaded at full torque for a period of time on one side of the gear teeth, then as the driver reverses gears, the teeth are loaded on the other side at full torque; again, for a while. Although the gear teeth DO experience full torque reversal, the cycle is not max positive to max negative; it's max positive for a while and then max negative for a while with a short time period in between torque reversals. I am curious to know if this torque cycle indeed qualifies as a full torque reversal cycle. If so, then the fatigue SN curve data need to be reduced by 30%... greatly affecting the gear tooth fatigue life. I am not sure, then, how to define a full reversal torque cycle pertinent to this application.
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