1. INTRODUCTION Automakers are expanding the availability of plug-in hybrid vehicles (PHVs) to help satisfy increasingly stringent automotive environmental standards around the world. As part of this trend, the development of the new Prius Prime aimed to achieve an appealing vehicle capable of meeting the expectations of customers by combining world-class environmental performance (i.e., power consumption efficiency and fuel economy) with greatly improved dynamic performance in electric vehicle (EV) mode. This paper describes the development of this new plug-in hybrid system, as well as its components and systems. 2. DEVELOPMENT OBJECTIVE 2.1 Dynamic Performance in EV Mode and Environmental Friendliness The first objective of this development was to create a highly efficient system with greatly improved dynamic performance in EV mode, while maximizing the performance of the hybrid system components in the new fourth generation Prius hybrid vehicle (HV) to maintain high-performance in HV mode [ 1]. At the same time, this development also aimed to improve the driving feeling of the PHV in EV mode. This high EV mode performance was achieved by increasing the output current and battery voltage of the power control unit (PCU), adding a new Dual Motor Drive System with a one-way clutch installed on the transaxle, and adopting a high-capacity battery pack system. In addition, a new battery warm-up system was developed to help improve EV mode dynamic performance in cold temperatures.2.2 Charging System Charging is an essential function for PHVs. This development increased the efficiency of the charging system and boosted the output of the charger with the aim of minimizing increases in charging time caused by the expanded EV mode range. The charging system also features a new charging function based on weekly scheduling. The new function includes a timer and coordinated control between the pre-air conditioning and battery warm-up system to help improve user friendliness. 3. CONFIGURATION OF PLUG-IN HYBRID SYSTEM Figure 1 shows the configuration of the plug-in hybrid system. Figure 1. Configuration of new plug-in hybrid system. The engine in the new Prius Prime is the same 2ZR-FXE engine used in the Prius HV . This engine has a peak thermal efficiency of 40%[ 2].Development of New Plug-In Hybrid System for Compact-Class Vehicle Shinji Ichikawa, Hiroaki Takeuchi, Shigeru Fukuda, Shigeki Kinomura, Yoshiki Tomita, Yosuke Suzuki, and Takahiko Hirasawa Toyota Motor Corporation ABSTRACT A next-generation plug-in hybrid system has been developed for the new Prius Prime. The objective of this development was to maximize the performance of the Toyota Hybrid System II (THS II) developed for the new fourth generation Prius HV , while achieving even better dynamic performance in electric vehicle (EV) mode. These objectives were accomplished by the adoption of new components and systems, as well as refinements to existing hybrid vehicle (HV) components. This paper describes the development of this new plug-in hybrid system. CITATION: Ichikawa, S., Takeuchi, H., Fukuda, S., Kinomura, S. et al., "Development of New Plug-In Hybrid System for Compact-Class Vehicle," SAE Int. J. Alt. Power. 6(1):2017, doi:10.4271/2017-01-1163.Published 03/28/2017 Copyright © 2017 SAE International doi:10.4271/2017-01-1163 saealtpow.saejournals.org 95Downloaded from SAE International by Univ of California Berkeley, Thursday, August 02, 2018The configuration of the plug-in hybrid system is essentially the same as in the Prius HV [1 ]. However, to improve performance in EV mode, the output of the boost converter in the PCU was increased. A new Dual Motor Drive System was also adopted, which is capable of using the generator in addition to the motor to drive the vehicle in EV mode. These improvements helped to greatly enhance EV mode performance. The traction battery system features a larger capacity battery than the Prius HV , which helps to substantially