Imamura, T., Tabata, A., Matsubara, T., Iwase, Y. et al., "Concept and Approach of Multi Stage Hybrid Transmission," SAE Technical Paper 2017-01-1098, 2017, doi:10.4271/2017-01-1098.
Lexus developed the Multi Stage Hybrid Transmission for the flagship Lexus LC500h coupe with the aim of achieving an excellent balance between fuel economy and acceleration performance. To gain these benefits, this transmission utilizes a multi-stage approach with the input split mode as an enabler for a concept of multiple high- efficiency points. In order to apply this approach to the transmission, a shift device was located immediately after a power split device. For functioning of the input split mode electrically-controlled continuously variable transmission, the power split device is connected with the motor, generator, and inverters. The optimal gear selection of the shift device to reduce the power loss in accordance with the driving state improves not only fuel economy but also heat management performance compared with the previous hybrid transmission. The Lower gears of the shift device that amplifies both the motor and the engine torque enhances acceleration performance compared with the previous hybrid transmission which amplifies only the motor torque. This paper describes the motivation for selecting the multi-stage approach with the input split mode from implementations of multiple high-efficiency points concept, and the potential of multi-stage approach with the input split mode compared to the previous hybrid transmission.