A design method for multi-mode power-split hybrid electric transmission considering mode continuity

Compared with single-mode power-split hybrid electric transmission, multi-mode power-split hybrid electric transmission can achieve high power, wide speed range, and high efficiency, which is the most suitable hybrid electric transmission scheme for heavy vehicles. Mode switching quality is the key factor restricting the application of multi-mode power-split hybrid electric transmission. Therefore, a design method for multi-mode power-split hybrid electric transmission which can ensure mode switching without speed difference is proposed. Firstly, based on the lever analogy method and analysis on characteristics of mechanical points, three conditions of mode continuity and methods to satisfy these conditions on function level are obtained. Then the design method can be divided into three steps: (1) design the function model of each mode scheme to achieve the conditions of mode continuity; (2) design the configuration of each mode scheme according to the function model and comprehensive consideration of mode continuity, structural simplification and operation logic, and combine the configuration of each mode into an integral scheme by arranging clutches/brakes; (3) inversely convert the lever model in the configuration scheme to planetary gear set to obtain specific transmission scheme. Finally, to demonstrate the feasibility of the design method, one of the design results is taken as an example to carry out mechanical structure design, kinematics and power flow analysis.