Abstract A numerical study is conducted to investigate the effect of changing engine oil and automatic transmission fluid (ATF) temperatures on the fuel economy during warm-up period. The study also evaluates several fuel economy improving devices that reduce the warm-up period by utilizing recycled exhaust heat or an electric heater. A computer simulation model has been developed using a multi-domain 1-D commercial software and calibrated using test data from a passenger vehicle equipped with a 2.4 / 4-cylinder engine and a 6-speed automatic transmission. The model consists of sub-models for driver, vehicle, engine, automatic transmission, cooling system, engine oil circuit, ATF circuit, and electrical system. The model has demonstrated sufficient sensitivity to the changing engine oil and ATF temperatures during the cold start portion of the Federal Test Procedure (FTP) driving cycle that is used for the fuel economy evaluation. The results from the study indicate that the potential fuel economy improvement during the driving cycle is 7.3 % at 24°C ambient temperature, and 20.1 % at −6.7°C. An electric ATF heater and two heat exchangers that recycle exhaust gas to heat ATF or engine oil have been evaluated in terms of fuel economy improvement. The study has discovered that the exhaust ATF heater has the greatest impact on the fuel economy during the warm-up period. According to the simulation results, the improvements are 2.1 % at 24°C ambient temperature, and 7.2 % at −6.7°C.Introduction In recent years, the focus of ongoing efforts to improve the fuel economy has shifted to the effect of advanced thermal management and exhaust heat recovery system on powertrain efficiency. A number of researches have been conducted to improve the powertrain efficiency by reducing parasitic losses by electrifying auxiliary components. Cho et al. [1] have conducted a simulation work on improving cooling system performance and fuel economy by electrifying coolant pump. Hnatczuk et al. [2], and Cortona et al. [3] also studied the effect of electrifying coolant pump on the fuel economy. Wagner et al. have investigated the effect of using electric coolant pump and control valve on engine thermal management [ 4,5]. Setlur et al. have studied the behaviors of smart valve, electric coolant pump, radiator with electric fan, and immersion heater in a simulation work [ 6]. An experimental and numerical study has been conducted to investigate the impact of electric coolant pump and fan, and electronic control valve on the fuel consumption characteristics of an Army medium tactical vehicle [7]. The main goal of the waste heat recovery system is to improve powertrain efficiency by converting the wasted exhaust heat to usable energy. The potential improvement is as much as 30 % of the energy content of the fuel burned [ 8,9]. Latz et al. [10], and Teng et al. [11 ] have studied Rankin cycle systems to recover waste exhaust heat. However, the majority of the Fuel Economy Improvement During Cold Start Using Recycled Exhaust Heat and Electrical Energy for Engine Oil and ATF Warm-Up2014-01-0674 Published 04/01/2014 Byungchan Lee and Dohoy Jung University of Michigan John Myers and Jae-Hoon Kang Hyundai-Kia America Technical Center Inc. Young-Ho Jung and Kwang-Yeon Kim Hyundai-Kia Motors CITATION: Lee, B., Jung, D., Myers, J., Kang, J. et al., "Fuel Economy Improvement During Cold Start Using Recycled Exhaust Heat and Electrical Energy for Engine Oil and ATF Warm-Up," SAE Technical Paper 2014-01-0674, 2014, doi:10.4271/2014-01-0674. Copyright © 2014 SAE InternationalDownloaded from SAE International by University of Liverpool, Sunday, September 09, 2018studies are focused on component level evaluations of such devices, and very few studies have been conducted to assess the impact of the advanced thermal management and the exhaust heat recovery system on the powertrain efficiency at a vehicle level. Kuze et al. have deve