Investigation of power split schemes for modern hybrid cars transmissions

Abstract

Abstract The modes of operation of the transmissions for hybrid cars are studied in this work, using planetary gears for connecting the internal combustion engine (ICE) and the electric machines (motor-generators). The peculiarities of the two-stream variants with an electric branch – a closing block consisting of two electric machines is analysed. This achieves a stepless gear change and an increase in overall efficiency with respect to the efficiency of electrical machines. The theoretical formulation is based on the dependences between the losses of a two-stream circuit, which proves that this increase is a function of the relative share of power transmitted through the electrical branch. The characteristics of typical two-stream circuits with input differential and output differential with one mechanical and one electrical branch are determined. The aim is to evaluate not only the change in the total efficiency, but also the kinematic gear ratio and the ratio of the torques and their ranges for the whole circuit, as a function of the parameters of the electrical branch. The development of the schemes in order to improve their performance in different operating conditions is considered, which allows for combining the variants and modes of operation – serial hybrid and parallel hybrid in two variants, at low speed and high speed. Analytical and graphical methods are used to analyse and illustrate the results, which are more visual and suitable for composite planetary gears with more units. It is expected that cars with such transmissions will have better dynamics compared to conventional automatic transmissions and lower energy consumption or do less damage to the atmosphere, as a result of the optimal combination of the operating modes and dimensions of ICE and electric machines.