Design and Control Methodology of Series–Parallel (Torque and Speed Coupling) Hybrid Drive Train

As discussed in Chapter 5, the series–parallel or, more accurately, the torque/speed-coupling hybrid drive train has some advantages over the series (electrical coupling) and parallel (single torque or speed coupling) drive trains. The torque and speed couplings in this drive train free the engine from the driven wheels in the torque and speed constraints. Consequently, the instantaneous engine torque and speed can be independent of the load torque and speed of the vehicle. Therefore, the engine can be operated in its high-efficiency region in a similar way as that of the series (electrical coupling) drive train. On the other hand, part of the engine power is directly delivered to the driven wheels without experiencing multiform conversion. 1 – 3 This feature is more similar to the parallel (torque or speed coupling) drive train.