Combined Fluid Loop Thermal Management for Electric Drive Vehicle Range Improvement

Abstract

Electric drive vehicles (EDVs) have complex thermal management requirements not present in conventional vehicles. In addition to cabin conditioning, the energy storage system (ESS) and power electronics and electric motor (PEEM) subsystems also require thermal management. Many current-generation EDVs utilize separate cooling systems, adding both weight and volume, and lack abundant waste heat from an engine for cabin heating. Some use battery energy to heat the cabin via electrical resistance heating, which can result in vehicle range reductions of 50% under cold ambient conditions. These thermal challenges present an opportunity for integrated vehicle thermal management technologies that reduce weight and volume and increase cabin heating efficiency . Bench testing was conducted to evaluate a combined fluid loop technology that unifies the cabin air -conditioning and heating, ESS thermal management, and PEEM cooling into a single liquid coolant-based system. This system has separate hot and cold fluid streams that are directed to the thermal components as required. The advantages include PEEM waste heat recovery to supplement cabin heating and heat pump operation without refrigerant cycle reversal. A bench test apparatus was constructed to apply transient drive cycle loads to the thermal system and measure the performance under ambient temperatures from −12°C to 43°C. The system proved capable of meeting component thermal requirements at all tested conditions. Furthermore, the system demonstrated a 9% range increase on a nationally weighted basis that accounts for vehicle usage and ambient temperature. The range improvement is expected to be greater for an optimized in-vehicle system.