An Integrated Electric Energy Management System to Improve Fuel Economy

Abstract

Fuel consumption and greenhouse gas emissions pose serious challenges to automotive industry. Today’s vehicles require much more electric energy due to the much wider array of electrical and electronic on-board comfort and safety systems. The balance of power delivery to different systems is becoming more and more difficult. In response to the growing need for more electric power, an integrated electric energy management system is introduced. An energy management unit (EMU) is the brain of whole system; it integrates charging management, auto start stop function, battery monitoring and electric load management. Based on the battery state of charge (SOC), EMU determines the strategy for energy management. The EMU controls charging voltage by a LIN connected alternator regulator to maintain SOC. When the battery soc is low, EMU increases the charging voltage to stimulate battery charging. But when soc is in a normal range, charging voltage is adjusted according to vehicle motion to improve fuel economy. The auto start stop function turns off and restarts engine automatically, when the battery SOC is in an appropriate status. EMU also determines which electric load the power should be preferentially supplied to when the battery SOC is low or when the alternator malfunctions. In these situations, the EMU will reduce electric power delivered to such components as a seat heater, for example, in order to ensure enough power for safety systems such as the x-by-wire systems. A closed-loop control of the battery SOC improves stability of electric power net. EMU increases the charging voltage when vehicle is decelerating, and decreases the charging voltage when vehicle is accelerating. Regeneration increases fuel efficiency while simultaneously enhancing driving dynamics. A continuous charging voltage adjustment way is introduced. This avoids the abrupt torque output, and improves NVH performance. Auto start stop function combined with charging management delivers more reductions in fuel consumption and CO2 emissions.