A Comprehensive Approach of the Lubrication for the Electric Powertrain Based on an Innovative Multi-purpose Fluid

Abstract

Because of the increasing power density of electric motors, it is anticipated that the oil would not only lubricate the gearbox, but it will also be used as a coolant for the electric motor. TOTAL Quartz EV-Drive MP Technology has been designed as an innovative multi-purpose fluid which meets the new requirements of the combination of electric motor cooling and transmission lubrication. A comprehensive approach which identifies all the new constraints was followed in order to design such a multi-purpose fluid. Oil needs to maximize the heat transfer. Numerical simulations of an electric motor coupled with the data generated on a Stator Cooling Test enable us to identify the electric motor hot spots and to determine the fluid cooling power. As oil will be in direct contact with electrical components, it needs to be electrically insulating to avoid any current leakage. A direct oil cooling system also implies that oil should be inert towards electric motor insulation materials and bare copper. Test rigs were used to assess the oil compatibility with copper and polymer coated wires. Another critical aspect of electric vehicles is the high-speed lubrication properties. Ball bearings could experience lubricant starvation when the electric motor runs at high speed. A High-Speed Ball Bearing Test was designed to assess our fluids in this regard. Transmission components are also running at high speed, which increases oil aeration and churning losses. A specific test rig has also been designed to characterize churning losses at high speed.