Relative to traditional internal combustion engine vehicles, electricdrive vehicles (EDVs) have increased vehicle thermal management complexity through the addition of a battery pack, also known as the energy storage system (ESS), as well as power electronics and electric motor (PEEM) components. These drivetrain subsystems have specific thermal requirements that have necessitated a separate thermal loop for each subsystem. The ESS must be cooled during hot ambient conditions to prevent degradation of battery cell life and must be heated during cold ambient conditions to enable adequate discharge power. The typical range of temperature control for the ESS battery cells is 15°C to 35°C [1]. The PEEM systems must be cooled so that they remain below their maximum operating temperature limits to prevent thermal damage or failure. The typical thermal limits for the PE and EM components are around 150°C [2,3].Separate cooling loops typically entail additional heat exchangers at the front end of the vehicle, water/ethylene glycol (WEG) coolant, piping, and WEG pumps. The disadvantage of multiple cooling loops is that they increase vehicle weight, aerodynamic drag, and fan/pump power, thus reducing EDV range. Due to the lack of abundant engine waste heat that is typically available in traditional vehicles, EDVs also suffer from significant range loss when heating the cabin in cold weather conditions. Cold-weather range loss can be as high as 50%[4], which reduces customer acceptance of EDVs by increasing range anxiety, and presents a barrier for the penetration of EDVs into the national vehicle fleet. The goal of the combined fluid loop (CFL) technology is to improve EDV range and reduce thermal system weight and volume by capturing the synergistic benefits of unifying the thermal management systems.The CFL technology being investigated unifies the cabin, ESS, and PEEM thermal management into a single coolant-based system with separate hot and cold fluid streams that are directed to the thermal components as required. The unified system has a single heat exchanger at the front end of the vehicle that either rejects or absorbs heat based on the CFL system's operating mode. The design of the system piping allows the coolant to be directed based on operating requirements, including actively heating or cooling the ESS, using the high-temperature coolant stream to cool the PEEM, and recovering the waste heat from the PEEM to supplement cabin heating. The CFL system also enables hot or cold coolant to be directed to the passenger cabin, which means that the system can act as either an air-conditioner or heat pump without reversing the refrigerant cycle. This is advantageous because refrigerant cycle reversal induces refrigerant charge and oil migration issues, as well as 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 requir...

Electric vehicles (EVs) need highly optimized thermal management systems to improve range. Climate control can reduce vehicle efficiency and range by more than 50%. Due to the relative shortage of waste heat, heating the passenger cabin in EVs is difficult. Cabin cooling can take a high portion of the energy available in the battery. Compared to internal combustion engine-driven vehicles, different heating methods and more efficient cooling methods are needed, which can make EV thermal management systems more complex. More complex systems typically allow various alternative modes of operation that can be selected based on driving and ambient conditions. A good system simulation tool can greatly reduce the time and expense for developing these complex systems. A simulation model should also be able to efficiently co-simulate with vehicle simulation programs, and should be applicable for evaluating various control algorithms. The MATLAB/Simulink dynamic system simulation environment, widely used in the automotive industry, effectively meets these criteria. To model the full EV thermal management system, the National Renewable Energy Laboratory's airconditioning model now incorporates liquid-coolant system components. In the full system model, lookup tables were used to characterize the components' performance. Predicted data obtained with the system simulation model were compared against experimental data. An agreement within 5% for most of the system parameters was achieved. The validated system model was then used to determine which of two possible locations for the power electronics and electric motor in the system is better for quick cabin heating starting from cold soak.

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The National Renewable Energy Laboratory's (NREL's) CoolSim MATLAB/Simulink modeling framework was expanded by including a newly developed coolant loop solution method aimed at reducing the simulation effort for complex thermal management systems. The new approach does not require the user to identify specific coolant loops and their flow. The user only needs to connect the fluid network elements in a manner consistent with the desired schematic. Using the new solution method, a model of NREL's advanced combined coolant loop system for electric vehicles was created that reflected the test system architecture. This system was built using components provided by MAHLE Inc. and included both air conditioning and heat pump modes. Validation with test bench data and verification with the previous solution method were performed for 10 operating points spanning a range of ambient temperatures between -2°C and 43°C. The largest root mean square difference between data and simulation results for pressure, temperature, energy and mass flow rate was less than 7%. A/C -air conditioning CFL -combined fluid loop EV -Electric vehicle NREL -National Renewable Energy Laboratory RMS -root mean square WEG -water-ethylene glycolThe Engineering Meetings Board has approved this paper for publication. It has successfully completed SAE's peer review process under the supervision of the session organizer. The process requires a minimum of three (3) reviews by industry experts.All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE International.Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE International. The author is solely responsible for the content of the paper.

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