Gahagan, M., "Lubricant Technology for Hybrid Electric Automatic Transmissions," SAE Technical Paper 2017-01-2358, 2017.
The automotive vehicle market has seen an increase in the number of hybrid electric vehicles (HEVs), and forecasts predict additional growth. In HEVs, the hybrid drivetrain hardware can combine electric motor, clutches, gearbox, electro-hydraulics and the control unit. In HEV hardware the transmission fluid can be designed to be in contact with an integrated electric motor. One transmission type well-suited to such hybridization is the increasingly utilized dual clutch transmission (DCT), where a lubricating fluid is in contact with the complete motor assembly as well as the DCT driveline architecture. This includes its electrical components and therefore raises questions around the suitability of standard transmission fluids in such an application. This in turn drives the need for further understanding of fluid electrical properties in addition to the more usually studied engineering hardware electrical properties. New understanding around the properties of transmission fluids in electric fields has been gained. This knowledge has been used to design a fluid with the appropriate electrical characteristics coupled with those essential performance characteristics for a fluid required to lubricate a DCT unit. Such a fluid technology recently developed to be suitable for a hybrid electric DCT unit, an eDCT, is described, as well as some of the more fundamental investigations underpinning its development.