Abstract Electrification of the powertrain to improve vehicle fuel economy is a key technology to achieve strict fuel economy legislation. However , only limited numbers of small class vehicles such as a B segment adopt electric powertrain. This is presumed that cost effectiveness for fuel economy is small and mounting space for additional powertrain is limited. In this paper, the optimum solution of a strong hybrid system suitable for the small vehicles was studied. First, from the viewpoint of maximization of energy efficiency, we compared contributions of engine efficiency and transmission efficiency during mode cycle driving and selected automated manual transmission as a suitable transmission for small vehicles. In comparing the hybrid system function, we determined a motor generator connecting shaft and a necessary motor generator output power for attaining both fuel economy and drivability. Further, motor generator and gear arrangement were designed to realize the shift change without torque interruption and shorter axle length than conventional manual transmission. The functional prototype of an automated manual transmission hybrid system and a test vehicle were built. Furthermore, we introduce vehicle evaluation result of the shift change sequence without torque interruption and the possibility of flexible drivability. Introduction In recent years, fuel economy legislation has become stricter because of global warming issue and energy consumption issue. Electric powertrain is effective for the improvement of fuel economy. Therefore several hybrid powertrains were developed [ 1],[2]. However, only limited numbers of small class vehicles adopt electric power train such as strong hybrid. This is presumed that cost effectiveness for fuel economy is small and mounting space for additional powertrain is limited.In this paper, AISIN SEIKI introduces an examination result of a hybrid system suitable for the small vehicles and Automated Manual Transmission Hybrid System (hereinafter, HV-AMT). Hybrid System Selection Electric powertrain is generally categorized based on electrified level and function ( Figure 1). Figure 1. Level of electrification and functions Strong hybrid system is focused in this paper in consideration of strict fuel economy legislation in the future. In order to select system type/structure, energy efficiency combining engine efficiency and transmission efficiency has been considered as a way of improving fuel efficiency. To improve engine efficiency, there was an idea to make an engine operating point concentrate on a high-efficiency area (optimization of operating point). Continuously variable transmission (CVT) has the advantage for achieving this function.Development of Hybrid Powertrain System for Small Vehicles 2016-01-1171 Published 04/05/2016 Shota Hirose, Akemi Okawa, Kenji Ishida, Takahiro Misu, and Takeshi Tojo Aisin Seiki Co., Ltd. CITATION: Hirose, S., Okawa, A., Ishida, K., Misu, T. et al., "Development of Hybrid Powertrain System for Small Vehicles," SAE Technical Paper 2016-01-1171, 2016, doi:10.4271/2016-01-1171. Copyright © 2016 SAE InternationalDownloaded from SAE International by University of New South Wales, Monday, August 27, 2018Figure 2 shows the simulation result of an engine operating point of the vehicle with 1L engine during LA#4 pattern driving. Figure 2. Engine operating point during LA#4 pattern driving As understood from Figure 2, small vehicle relatively often uses an engine high-efficiency area even during certification drive pattern such as LA#4. CVT has slight advantage to stepped T/M in small vehicle class. Next, Figure 3 shows characteristics of transmission efficiency of representative T/Ms. Figure 3. Characteristics of representative T/Ms. AMT and DCT which do not use hydraulic pressure during driving without shift change have the highest transmission efficiency. AT which applies hydraulic pressure to keep gear step using wet type clutch