INTRODUCTION Compliance with global strengthening of emission regulations is an urgent issue for the automobile industry. The final solution for this requirement should be to putting zero- emission vehicles, such as BEV (Battery Electric Vehicle) or FCEV (Fuel Cell Electric Vehicle) into practical use. However, they could not be a suitable replacement of conventional cars because of their limited driving range and higher cost due to current technical limitations. Therefore, HEV (Hybrid Electric Vehicle) application has been expanding globally as one of practical solutions. A new two-motor plug-in hybrid system which realizes both environmental friendliness of zero-emission vehicles and practicalities of HEVs is developed to satisfy this situation and main features are discussed in this paper. OVERALL CONFIGURATION The major components of the new two-motor plug-in hybrid system are placed in the vehicle as shown in Figure 1. An electric coupled CVT (e-CVT) is installed in the position of a conventional transmission and utilized in combination with an Atkinson cycle engine optimized for HEV application. The PCU (Power Control Unit) is positioned above the e-CVT and cooled by an independent water cooling circuit separated from the engine. Various functions including high-voltage inverters, VCU (Voltage Control Unit) and motor/generator ECU (Electric Control Unit) are integrated in the PCU. IPU (Intelligent Power Unit) is installed behind the rear seats and cooled by cooling fans located in the trunk room. A Li-ion battery specially designed for plug-in hybrid, a DC/DC converter, a high-power on-board charger and a battery ECU constitute the IPU as one package. Figure 2 shows a structure of the IPU. 2013-01-1476 Published 04/08/2013 Copyright © 2013 SAE International doi:10.4271/2013-01-1476 saealtpow.saejournals.org Development of a New Two-Motor Plug-In Hybrid System Naritomo Higuchi, Yoshihiro Sunaga, Masashi Tanaka and Hiroo Shimada Honda R&D Co., Ltd. ABSTRACT A highly efficient two-motor plug-in hybrid system is developed to satisfy the global demands of CO 2 reduction. This system switches three operation modes, what is called “EV Drive”, “Hybrid Drive” and “Engine Drive”, to maximize fuel efficiency according to the driving condition of the vehicle. Practical plug-in EV (Electric Vehicle) capability is also realized by adding a high-power on-board charger and a high capacity Li-ion battery to the original system. The outlines of the system components including a newly developed Atkinson cycle engine, a highly efficient electric coupled CVT (Continuously Variable Transmission) with built-in motor and generator, an integrated PCU (Power Control Unit) and an exclusive battery for plug-in HEV (Hybrid Electric Vehicle) are described in this paper. In addition to the switching of three driving modes and the efficiency improvement of each device, cooperative control of the hybrid system is introduced. By installing this system in 2014 Accord plug-in hybrid, superior fuel economy is achieved with values of 46 MPG in CS (Charge Sustaining) mode and 115 MPGe (Miles Per Gallon equivalent) in CD (Charge Depleting) mode. 13miles of AER (All Electric Range) is also achieved while maintaining sufficient driving performance as a mid-size sedan. MPGe is a unit of fuel economy for the alternate fuel vehicles such as plug-in hybrid or electric vehicles. The ratings are calculated by converting used electric energy into equivalent amount of gasoline. CITATION: Higuchi, N., Sunaga, Y., Tanaka, M. and Shimada, H., "Development of a New Two-Motor Plug-In Hybrid System," SAE Int. J. Alt. Power. 2(1):2013, doi:10.4271/2013-01-1476. ____________________________________ 135Figure 1. Overall system configuration Figure 2. IPU (Intelligent Power Unit) POWER TRAIN Overview An overview of the power train is shown in Figure 3 and operation modes of this system are explained in Table 1. This system can be operated in three operation modes ex