Abstract To help respond to growing customer demand for environmentally friendly vehicles, a new transaxle for plug-in hybrid vehicles (PHVs) has been developed that achieves excellent fuel economy and ensures high performance when the PHV operates in electric vehicle (EV) mode. Under the basic concept of sharing a large number of parts with the transaxle in the all new Prius, the newly designed PHV transaxle was developed with the aim of enhancing EV power and range. To achieve our goal, the new transaxle uses a Dual Motor Drive System that operates the generator as a motor to supplement the existing motor. It also features an electrical oil pump (EOP) that improves cooling performance in EV mode. The developed transaxle helps to advance the PHV as a key next-generation environmentally friendly vehicle by maximizing the performance of the Toyota Hybrid System (THS) and achieving even better dynamic EV mode performance than the new Prius HV . 1. Introduction Customer awareness of the global environment and requirements for environmental performance has continued to rise since the launch of the first generation Prius in 1997 as the world’s first mass-production hybrid vehicle (HV) [ 1, 2, 3]. Furthermore, as environmentally friendly vehicles have become more widespread, customers have also started to require higher levels of dynamic performance and style in addition to excellent fuel economy. We have listened to our customer’s feedback who voiced their desire to drive their PHV in EV mode without engaging the engine, hence requiring greater driving force and range in EV mode. Therefore, this transaxle was developed to greatly increase dynamic EV performance under the concept of utilizing the components and capabilities of the THS in the new fourth generation Prius as far as possible. This paper introduces the new PHV transaxle for compact vehicles that is installed in the all new Prius Prime.2. Development Aims The development objectives of the new PHV transaxle were as follows: 1. Help achieve powerful EV mode driving force by placing a one- way clutch between the engine and power split device to realize the Dual Motor Drive System, which enables the vehicle to be driven using two motors. 2. Help achieve powerful EV mode driving force and greatly extend the EV mode driving range by enhancing the cooling performance of the planetary gear and motor during EV mode through the use of an EOP. 3. Utilize the existing components and capabilities of the HV transaxle in the Prius HV [4] when possible to maintain high performance in HV mode while also greatly improving performance in EV mode. 3. Basic Specifications and Structure Figures 1 and 2 show a cross section and a schematic of the developed PHV transaxle. Table 1 shows the main specifications. The PHV transaxle has a four-axis structure and consists of a torsional damper with a torque limiter, one-way clutch, input shaft, planetary gear, generator, motor, reduction device, and differential device. The planetary gear functions as the power split device that determines whether engine power is supplied to the generator or used as vehicle driving force. The motor and motor reduction gear are laid out on a different axis to the input shaft, and the motor speed reduction device uses a parallel shaft layout. Power is applied from both the engine and motor to the counter driven gear, which transmits this power to the differential gear. In EV mode the one-way clutch receives the reaction torque of the generator and transmits it to the tires when high driving force is requested by the driver.Development of New Plug-In Hybrid Transaxle for Compact- Class Vehicles2017-01-1151 Published 03/28/2017 Yosuke Suzuki, Akiko Nishimine, Shinichi Baba, Kenji Miyasaka, Michitaka Tsuchida, Hiroatsu Endo, and Norihiro Yamamura Toyota Motor Corporation Tomoyuki Miyazaki NSK-Warner K.K. CITATION: Suzuki, Y ., Nishimine, A., Baba, S., Miyasaka, K. et al., "Developm