Kumazaki, K., Matsubara, T., Kobayashi, N., Kato, S. et al., "Development of Shift Control System for Multi Stage Hybrid Transmission," SAE Technical Paper 2017-01-1150, 2017, doi:10.4271/2017-01-1150.
Toyota Motor Corporation developed a new hybrid system, Multi Stage Hybrid System, for the Lexus flagship coupe LC500h 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, the new hybrid system improves fuel economy by reducing electrical loss in the optimal gears, which are selected depending on the driving state. The system also improves acceleration performance by increasing the driving force at low and medium vehicle speeds in lower gears. In addition, the range of the power split device that cooperates with the shift device was widened to enable both an electrically-controlled continuously variable transmission mode and a ten-speed transmission mode, which creates a direct shift feeling to improve driving pleasure.This system contains many independent variables given by the interactions of the engine, generator, motor, and shift device. Thus, conventional control methods were not appropriate for devising the shift control of the system. In addition, shift performance may also be affected by the particular constraints of a hybrid system, such as battery limitations.This paper describes the shift control system for the Multi Stage Hybrid Transmission that was developed to resolve these issues.