30 Tribologie + Schmierungstechnik · 67. Jahrgang · 4/ 2020 The driveline architectures for hybrid and electric vehicles are significantly different from conventional manual or automatic transmission and axles. The powertrain architectures of hybrid and electric vehicles can be classified into three main types; series, parallel, and Power- Split. The parallel hybrid transmission architectures are divided into five categories depending on the location of electric motor. The P0 and P1 architectures are defined by the position of electric motor in the front or back of the engine respectively. Similarly, P2 and P3 are defined by the position of the electric motor on the front or the back of the transmission respectively. In P4 architecture, the electric motor is on the axle as shown in Figure 1. Driveline Fluid Opportunities for Hybrid and Electric Vehicles Arup Gangopadhyay, Prasad Dev Hanumalagutti* The sale of plug-in hybrid and electric vehicles is steadily increasing worldwide and first time it exceeded one million units in 2017. The 2019 sale is expected to be 2.8 million units (1). China leads the sale volume followed by United Sates and Europe. It is projected that electric and hybrid vehicles will account for an estimated 30 % of all vehicle sales by 2025 (2). In North America, 4 % of vehicles sold in 2018 consists of hybrid, plug-in and electric vehicles, substantial increase over previous years. Abstract * Arup Gangopadhyay and Prasad Dev Hanumalagutti Ford Motor Company Research and Advanced Engineering, Dearborn, Michigan USA Figure 1: The powertrain architectures of hybrid and electric vehicles Figure 2: The PowerSplit transmission architecture Aus Wissenschaft und Forschung / TAE-Plenarvorträge Aus Wissenschaft und Forschung / TAE-Plenarvorträge 31 Tribologie + Schmierungstechnik · 67. Jahrgang · 4/ 2020 The P4 architecture is more suited for electric vehicles. In P2, P3, and P4 architectures, the electric motor reside in the housing of the device; be it a transmission or an axle. In PowerSplit transmission, the power from the engine flows to the transmission planetary gear set which is also connected to the generator motor. The planetary gear set is connected to the traction motor through the transfer gear. The traction motor transfers power to the wheels through the final drive gear as shown in Figure 2. There is no clutch in this design. However, in P2 arrangement, the transmission could be multispeed (eight speed or higher) automatic with a torque converter and a set of clutches while an electric motor is connected to the torque converter. In the e-axle design the speed of the electric motor is reduced through a set of gear arrangement before power flows to the wheels. Both PowerSplit transmission and e-axle are filled with ATF. The electric motors gets quite hot during operation and the motor windings are cooled by automatic transmission fluid (ATF) dripping on it. Keeping the motor cooler allows (a) passing more current through it to deliver high torque, and / or (b) reduce the size of the motor to enable packaging under the hood. Therefore, ATF with improved thermal properties is very important. The desire is to achieve a drop in winding temperature of 15 °C, which according to a thermal model would require 50 % improvement in thermal conductivity. Also, copper corrosion is important although copper wire is mostly coated, there are areas which are not (i.e, welded joints). Therefore the next generation fluid should function both as a lubricant and as a coolant and additionally should have · improved thermal conductivity (50 %) · Improved copper corrosion · Improved oxidation · Material compatibility with laminates, insulators and rare earth metals in the electric motor There is limited thermal conductivity, and specific heat data in the literature and the base oil primarily govern fluid thermal properties. It appears thermal properties of Group l through Group III oils are quite similar. PAO (polyalpha olefin) offers an enhancement but not to the extent desired. Therefore, more attention may be paid on Group V base oils. Nanofluids are claimed to offer improved thermal conductivity and probably should be explored provided a stable suspension can be maintained along with tribological properties. References [1] “The Global Electric-Vehicle Market is Amped up and on the Rise” - McKinsey and Company, May 2018, https: / / www.mckinsey.com/ industries/ automotive-andassembly/ our-insights/ the-global-electric-vehicle-market-is-amped-up-and-on-the-rise. [2] “Driving into 2025: The Future of Electric Vehicles” J. P. Morgan Estimate, Oct 10, 2018, https: / / www.jpmorgan.com/ global/ research/ electric-vehicles