ABSTRACT Recently, due to mounting concerns regarding the environment and energy conservation, demand for compact and hybrid vehicles with good fuel economy has been increasing. Toyota Motor Corporation has developed its first hybrid transaxle for installation in sub-compact class vehicles. This new hybrid transaxle is both smaller and lighter than the P410 hybrid transaxle for compact class vehicles, including the 2009 Prius. This was accomplished by creating new designs of the gear train, motor, and motor cooling system, and by adopting advanced technology. This paper describes the major features and performance of this transaxle in detail. 2. INTRODUCTION In recent years, due to mounting concerns regarding the environment and energy conservation, it has become even more important to reduce CO 2 emissions from automobiles and improve fuel efficiency. Hybrid vehicle technology that combines an engine with a motor/generator is an important way of improving vehicle fuel efficiency. In 1997, the world's first mass production hybrid system was developed and installed in a compact class vehicle [ 1, 2, 3]. Since then, many improvements have been made to this hybrid system. A new transaxle (called the P112 transaxle) was developed in 2003 as part of a second generation hybrid system for installation in compact class vehicles [ 4]. In 2005, the P310 hybrid transaxle with a new motor speed reduction device was developed for use in SUVs [ 5]. Then, in 2009, the P410 hybrid transaxle was developed, which adapted the configuration of the P310 for use in compact class vehicles [6]. In order to further popularize hybrid vehicles, a hybridtransaxle for sub-compact-class vehicles is essential. Previously, Toyota Motor Corporation didn't have it. In response to such circumstances, the new P510 hybrid transaxle has been developed for installation in sub-compact class vehicles. This paper describes the structural characteristics and major features of this new P510 hybrid transaxle. 3. DEVELOPMENT OBJECTIVES The development objectives of the new hybrid transaxle for sub-compact class vehicles were to reduce size and weight and to improve performance (motor cooling performance, mechanical loss, and quiet operation). (1) Size and weight reduction To enable installation in sub-compact class vehicles, it was necessary to reduce the size and weight of the transaxle compared to the P410 transaxle, which is used in compact class vehicles. To achieve this, the motor speed reduction device and compound gear utilized in the P410 were adopted. Furthermore, the counter and differential gear size, and the center distance among the axes were reduced by making the motors smaller. The front overhang and engine hood line of the vehicle were reduced by adopting these technologies. (2) Performance improvement The motor cooling system was newly designed to improve the motor cooling performance of this new hybrid transaxle. To achieve top-class fuel efficiency, ATF (Automatic Transaxle Fluid) agitation loss was reduced. Furthermore, Development of New Hybrid Transaxle for Sub- Compact-Class Vehicles2012-01-0623 Published 04/16/2012 Tomoaki Furukawa, Ryuji Ibaraki, Hiroaki Kimura, Koichi Kondo, Masato Watanabe, Tatsuhiko Mizutani , Hiroyuki Hattori and Akira Takasaki Toyota Motor Corporation Copyright © 2012 SAE International doi:10.4271/2012-01-0623Downloaded from SAE International by Univ of California Berkeley, Sunday, August 05, 2018quiet operation was achieved by using CAE analysis to optimize a transaxle structure. 4. BASIC SPECIFICATIONS AND STRUCTURE Figure 1 shows the main cross section of the new P510 hybrid transaxle and Table 1 details its main specifications. The P510 uses the motor speed reduction device and compound gear utilized in the P410. With adoption of the motor speed reduction device, the P510 used the high rpm motor and shortened its overall length. The compound gear eliminated the need for the chain required in the conventional P112