1. INTRODUCTION In 2006, Lexus introduced the GS450h, equipped with the Lexus Hybrid Drive (LHD) system developed for rear-wheel drive (RWD) passenger vehicles. This system was later adopted for the all-wheel drive LS600h in 2007 as well. At the core of system was the hybrid transmission with a two-stage motor speed reduction device [ 2]. While providing superior fuel economy, the acceleration performance of this hybrid system is also highly regarded by drivers of competing vehicles. Since the introduction of these vehicles, various refinements have been applied to the hybrid transmission, adding to the already major contributions made towards reducing CO 2 emissions. However, in recent years, increasing awareness of environmental pollutions have created growing demand for various types of low-emission vehicles, as even more stringent emissions regulations are being announced across the globe. In an effort to develop and popularize vehicles with even higher environmental performance, automakers around the world have been actively developing eco- friendly vehicles, and a wide range of systems have been launched. Competition in the market is has never been higher. Even in the luxury coupe market, dominated by vehicles with excellent dynamic performance, hybridization has become a trend, as still higher levels of fuel economy and acceleration performance are in demand.To achieve supreme balance between fuel economy and acceleration performance in the RWD coupe market, Toyota has developed the Multi Stage Hybrid System. By combining this system with a V6 engine, the all new LC500h achieves a 0-to-60 mph time of 4.7 seconds and 30.0 mpg of combined fuel economy, all the while meeting SULEV requirements for exhaust emissions. At the core of this system is the newly developed Multi Stage Hybrid Transmission, including a shift device located immediately after the power split device and motor. 2. DEVELOPMENT OBJECTIVES The development objectives of the Multi Stage Hybrid Transmission (L310) are as follows. 1. The adoption of a shift device with a wide gear ratio range to maximize the potential fuel economy and acceleration performance of the transmission, and a step ratio that ensures high quality shifts.( Section 4 ) 2. The adoption of a quickly responsive and accurate hydraulic control system to achieve high quality shifts. ( Section 5 ) Development of Multi Stage Hybrid Transmission Koichi Okuda, Yuji Yasuda, Masatoshi Adachi, Atsushi Tabata, Haruhisa Suzuki, and Kiyonori Takagi Toyota Motor Corporation Tomoo Atarashi and Ryuta Horie AISIN AW Co.,LTD. ABSTRACT Toyota Motor Corporation developed the Multi Stage Hybrid System for the Lexus flagship LC500h coupe with the aim of achieving an excellent balance between fuel economy and acceleration performance. The Multi Stage Hybrid Transmission used in this new hybrid system includes a shift device located immediately after the power split device and motor. Compared with previous hybrid systems, acceleration performance is improved by increasing the driving force at low and medium vehicle speeds in lower gears, fuel economy and heat management performance are improved by reducing electrical loss by selecting the optimal gear depending on the driving state. The Multi Stage Hybrid Transmission uses a shift device with a wide gear ratio range to maximize both fuel economy and acceleration performance. The transmission was designed to achieve the appropriate size to be mounted in a new platform, as well as class-leading low noise levels for adoption in luxury vehicles. It also includes a quickly responsive and accurate hydraulic control system that achieves excellent shift performance. This paper describes the hardware of the Multi Stage Hybrid Transmission. CITATION: Okuda, K., Yasuda, Y ., Adachi, M., Tabata, A. et al., "Development of Multi Stage Hybrid Transmission," SAE Int. J. Alt. Power. 6(1):2017, doi:10.4271/2017-01-1156.Published 03/28/2017 Copyrigh