Energy-efficiency improvement potential of electric vehicles considering transmission temperature

This study presents an integrated energy and transmission thermal management system to quantify the impact of a cold-start on the energy consumption of electric vehicles (EVs) from optimal control perspective. In addition, it provides insights into reducing this cold effect from design point of view. The cold-start conditions in an EV refer to a low transmission temperature, which increases the frictional power losses caused by viscosity effects in the transmission. These losses are eventually compensated by the battery, leading to excess energy usage. A detailed EV model, especially the transmission part with transient thermodynamics based on experiment data, is developed, and the integrated energy and thermal controller aims to maximize the energy efficiency. Numerical results show that a cold-start influences the energy-saving potential, up to 2.9%. Through analysis of temperature-dependent transmission behavior and energy losses of the EV, design considerations of reducing the cold impact, thus improving energy efficiency, can be derived.