Enhancing the efficiency of electric vehicle’s motor using electro-mechanical continuously variable transmission

Abstract

Over the last decades, significant progress has been made on the technologies of battery electric vehicle (BEV) powertrain system. As a result, the driving mileage of the latest EVs has been improved tremendously, making the ownership of BEV more viable now. Nevertheless, even with the latest progress, the driving mileage of a BEV is still generally lower as compared to the vehicle with an advanced internal combustion engine. Thus, this paper investigates the potential of increasing the mileage of a BEV further by using electro-mechanical continuously variable transmission (EMCVT) in its powertrain system. The purpose of the EMCVT is to allow the electric motor used in the BEV powertrain system to operate in its most efficient condition for a wide range of vehicle’s speeds. This condition is defined using the efficiency mapping of a typical electric motor applied in the existing BEVs. Based on this mapping, the motor’s efficiency when used with EMCVT is compared with the efficiency of the same motor when used with a single speed transmission for various vehicle speeds. In this investigation, the efficiency of the EM CVT is considered at 75% to 95%, and the BEV with EMCVT is considered to be 80 kg heavier than the BEV using a single speed transmission. The comparison between the BEV with and without EMCVT shows that the application of EMCVT allows the motor to operate in its most efficient condition for a wider range of the vehicle’s velocity. However, the improved motor’s efficiency is compromised by the losses in the EMCVT, making it challenging to achieve lower power consumption during driving. Therefore, to achieve meaningful improvement in terms of power consumption, the efficiency of the EMCVT has to be higher than 85%.