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In many rolling or sliding contact mechanisms, like roller bearings, journal bearings, gearings or any contact between two semi-infinite bodies, concentrated stress occurs at the edges of the contact. This stress, due to what is called edge effect, is known to be very fatigue damaging. To avoid this concentrated stress in common roller bearings, the rolling surface of the roller and/or of the track is crowned. The crowning shapes usually include a straight line and one or several circular arcs. Even if such crowning profiles are efficient in avoiding edge effects, they are far from being optimized in terms of contact pressure distribution. In recent years, crowning shapes based on a logarithmic function developed by Lundberg have been improved and optimized for the purpose of industrialization. However, the resulting profiles are fairly complex and have only been developed for roller bearings and not for other types of rolling or sliding contacts.

MCE-5 DEVELOPMENT has been developing its variable compression ratio engine (VCRi) for over a decade aiming at reducing fuel consumption and pollutant emissions. In order to transmit power from the piston (combustion) to the crankshaft, the MCE-5 VCRi technology is based on three innovative components: a gear wheel and two racks. This gear mechanism ensures a very low friction compared to other continuous VCR solutions based on bearings. However, this transmission is used in nonstandard conditions: the direction of rotation is reversed repeatedly, and the parts are submitted to high and rapidly varying loads. To avoid interferences and alteration caused by high contact pressure at high load, and ensure a regular transmission at low load, the profile of the teeth is carefully considered. A crowning shape is placed on the teeth in the direction of the gear axis, and a correction is applied to the tooth active profiles in the area of tooth roots and tooth tips.