Effect of Geared Transmissions on Electric Vehicle Drivetrains

The paper describes some simple modelling to investigate whether there are potential benefits to incorporating a geared transmission in electric vehicle driveline. The overall conclusion is that considerable benefits in energy consumption are available if a continuously variable gearbox system is incorporated; performance improvements of 6 to 19.2% are predicted over a range of European, USA and Japanese driving cycles. Furthermore, the use of a much simpler, two speed gearbox an improve performance significantly — by for example 9.2% over the NEDC cycle — although similar improvements are not predicted over other driving cycles. Overall, the results suggest not only that direct benefits in terms of energy reductions are obtainable, but also that significant reductions in motor and driveline sizing may be an alternative approach to exploiting the introduction of a transmission system.