A new solution for increased performance and low weight for electric vehicle transmission gears

The majority of vehicle powertrains rely on lubricated gear pairs to a given extent. Gear pairs despite their inherent high efficiency, still experience mechanical losses upon teeth contact. With the advent of Battery Electric Vehicles, facing charging time challenges as well as availability and limited infrastructure, infra-structure, a long driving ranges are key. Although the most direct solution is a larger battery pack, this comes at a steep cost and weight increase. Thus, loss reduction, of any sort, will offset the need for greater battery capacity. Furthermore, there is high demand to reduce material waste and the environmental impact of Battery Electric Vehicles.

Powder Metal Gears have an increased material utilization rate yielding a net positive environmental impact by reducing material waste whilst surface treatments methods, improve efficiency and therefore reduce the vehicle’s environmental impact. Also, all improvements in this area would represent a leap forward on Electric Mobility and electrification.

This Project aimed at evaluating the potential power loss reduction of different mechano-chemical surface treatments applied to Powder Metal Gear at different loads and speeds on a controlled environment through a standardized FZG rig.

The samples’ surface roughness was measured to characterize the differences between different treatments in comparison to the reference, an untreated gear pair. As an extension of the project, a pitting test was conducted with the same samples used in the mechanical losses characterization, aiming to verify potential durability improvements.

The improvement is consistent across all load stages and more prominent as load increases. Regarding pitting and lifetime effects further investigations are required to explain the inconsistency of the results and also extended test scope dedicated for the Pitting purpose.

Regarding the roughness, Ra showed a positive trend related to the efficiency, but no numerical calculation could be confidently described. Further research is required to define the correct metric correlating surface finish and efficiency. The surface treatment affects not only the surface roughness, but also introduces tribologically favorable chemicals, contributing to reduced friction losses.