Continuously Variable Power-split Transmission with a Step Gear Set: Fuel Economy & Performance Improvement

Recently, continuously variable transmission (CVT) has been much more applied in vehicles as it has several advantages such as smoothly gear changing and allowing engine operate at optimum speed. However, there are some important drawbacks which are low efficiency power transmission, especially at low speed (high torque) condition, limited belt torque capacity, and narrow overall gear ratio range, with which the CVT is limited to use in only small vehicles. To overcome these weak points and simultaneously keep the advantages of CVT, a planetary gear train (PGT) and a step gear box are implemented to the traditional CVT system called continuously variable power split transmission (CVPST) with step gear box system. The power from the engine will be separated into two ways; PGT and CVT. As the higher efficiency of PGT than CVT, the overall system efficiency will increase. Also, because only a part of the total power will go through the CVT set, the torque capacity of the overall system can be extended. The additional step gear box is used to enhance the overall gear ratio range. By simulation, the fuel economy and 0-60 time performance of both transmissions can be compared.