eJournals International Colloquium Tribology 23/1

International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231

Test Method to Determine Improvements of E-Drive Efficiency

125
2022
Michael Schulz
ict2310159
23rd International Colloquium Tribology - January 2022 159 Test Method to Determine Improvements of E-Drive Efficiency Dipl.-Ing. (FH) Michael Schulz ISP Salzbergen GmbH & Co. KG Contact: m.schulz@isp-institute.com Electrification of mobility is continuously increasing and the pace is even higher than expected. As a consequence, Battery Electric Vehicle (BEV) population is growing rapidly and a significant market share is expected in the future. Even though BEVs are rated as a highly efficient mobility concept, there is still room for improvement of e-drive units’ (EDU) efficiency and performance, with the increase of the driving range being a key element. Aside from design changes, mechanical and software improvements, the lubricant of the step gear and the cooling fluid which controls the temperature of the e-motor and power unit can also contribute to these improvements. So far, no standards are available to determine the influence of those e-fluids on the efficiency of the respective driveline. ISP developed a test method to demonstrate the potential for efficiency gains that are possible with dedicated low viscosity fluids. The test method describes how to set up the test stand, control the operation and gives a guideline for the most efficient way of testing. The development was done on a Volkswagen, first generation EDU, which is used in the Golf Mk. 7 and E-up vehicles. Fig. 1 shows the test matrix which has been defined for the first part of the development. Thirty four individual speed/ load steps have been measured to identify the areas of high potential for efficiency increases. Fig. 1: Running Order of the Speed / Load Matrix 160 23rd International Colloquium Tribology - January 2022 Test Method to Determine Improvements of E-Drive Efficiency The running order was selected in a way that the fluid temperature increases constantly from step to step in order to keep the stabilisation time of the temperature at a minimum. The mechanical power output was controlled to the set-point and the electrical input power measured, the difference between the two power levels has been calculated as system efficiency. A 3-D efficiency mapping was plotted (Fig. 2) based on the measurements which were taken at the end of each speed/ load step. Fig. 2: 3D Efficiency Mapping of the EDU For the determination of the efficiency gains of two different fluids, it has been assumed that the efficiency of the electric motor is constant and all differences which have been measured are linked to the transmission fluids. This assumption was based on the fact that the e-motor cooling was externally controlled and the ambient conditions kept constant over the whole measurement test development programme. As a result of this, efficiency improvements of over 3% were measured between the two different fluids. In the second phase of the test method development, Worldwide Harmonized Light Vehicles Test Cycles (WLTC) were performed. For the start of the first WLTC the fluid was conditioned to -10 °C and 23 °C, following which no further control was done on the fluid temperature and only the e-motor coolant and the ambient temperature controlled to the given set points. Fluid temperature differences of up to 5 K were measured and an efficiency improvement of 1.7 % confirmed the reduced friction of the low viscosity fluid against the conventional lubricant in the WLTC. Although the volume of the e-fluid in the system is quite low, it has been demonstrated that the efficiency with the introduction of low viscosity fluids can be improved significantly. Dedicated additive technology which also reduces friction and oil foaming can improve this benefit even further. Additional improvements are also expected from the cooling efficiency of integrated systems and EDUs where the fluid takes over the e-motor cooling in addition to the lubrication of the step gears. Further R&D on EDUs is expected in the coming years and this general test method can be adapted to current and future technologies to support the hardware and fluid development.