Title:
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Reliability of automotive transmission bearings
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The manufacture of rolling element bearings, as high precision mechanical components,
has experienced remarkable advances in the last few decades. Some of the key factors for
these advances include the incorporation of computer numerical control in machining,
improvements in the quality of lubricants and improvements in the cleanliness of the steel.
This in turn, has led to the highest ever level of reliability not only of the rolling bearing as
a unit but of the whole mechanical assembly where the rolling bearing is destined to work.
However, under high performance running conditions, such as in automotive transmissions,
intrinsic and/or external factors can hinder the rolling bearings from performing as expected
and as a result, premature failure may occur.
In this context, the present PhD thesis investigates the premature and recurrent failure of
a specific type of roller bearing, identified by its model number as 30206, when used as the
tail bearing of a particular automotive rear differential unit. For this, a series of theoretical
and practical approaches are used first, to characterise the failure, secondly, to propose
failure hypotheses and lastly, to evaluate the hypotheses.
From the forensic studies carried out on in-field-used bearings, three failure hypotheses
are proposed; in these, the mechanisms of fretting, static overload and corrosion are
respectively regarded as precursors to surface-initiated rolling contact fatigue. For the
evaluation, 'pre-damaged' bearings, representative of each failure hypothesis, are first
generated via various mechanisms and then tested in a bespoke made rolling contact fatigue
test rig.
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