Controller-free ratio-variable gearbox for parallel hybrid powertrain

A transmission from the engine crank to the main transmission with variable reduction ratio is desirable for the hybrid electric vehicles, especially for micro/mild hybrid vehicles with auto start-stop function, for the sake of reducing the design requirements for integrated starter-generator and thus reducing the cost. This paper presents a solution to the issue by introducing a Controller-Free Ratio-Variable gearbox. Unlike other solutions, the proposed gearbox avoids from using actuators to change gear ratios but realize the function in a purely mechanical and fully automatic way. This feature reduces system complexity and improves system stability, as electronic-based info sensing and actuating are not as robust in the engine compartment. Also, the feature allows to change gear ratio faster and thus better protecting integrated starter-generator from over speeding. In this paper, the principle of the gearbox is explained and its performance under different conditions is studied.