Experimental investigation of efficiency losses in a two speed electric vehicle

Publication Type:
Conference Proceeding
8th Australasian Congress on Applied Mechanics, ACAM 2014, as Part of Engineers Australia Convention 2014, 2014, pp. 23 - 32
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Electric vehicles (EV) are considered a practical alternative to conventional and hybrid electric passenger vehicles, with higher overall powertrain efficiencies by omitting the internal combustion engine. As a consequence of lower energy density in the battery energy storage as compared to fossil fuels powered vehicles, EV powertrains have limited driving range, leading to a range phobia and limited consumer acceptance. Particularly for larger luxury PEVs, electric motors with a single reduction gear typically do not achieve the diverse range of function needs that are present in multi-speed conventional vehicles, most notably acceleration performance and top speed requirements. Subsequently, multi-speed EV powertrains have been suggested for these applications. Through the utilisation of multiple gear ratios a more diverse range of functional needs can be realised without increasing the practical size of the electric motor. This paper builds on previous research to conduct an experimental investigation of the losses present in a multi-speed EV powertrain. The major limitation of multi-speed EV powertrains is that the increased transmission complexity introduces additional losses to the vehicle. Utilising the UTS Powertrain test rig the instantaneous losses of a multispeed and comparative single speed powertrain are investigated under the NEDC driving cycle, combining urban and highway style driving modes. This includes the power throughput evaluation of motor/controller and transmission, and the parasitic losses associated with control of clutch solenoids and the electric hydraulic fluid pump. The results demonstrate that while the single speed EV has improved overall efficiency by comparison to the multispeed equivalent powertrain, the comparative efficiencies are unlikely to significantly degrade the vehicle driving range.
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