Currently automobile industries are shifting towards electric powertrains from conventional internal combustion engines. With increase in use of electric vehicle, more focus is to increase the driving range of vehicle. Right now, most of the OEMs are using single speed transmission in their electric buses. Single speed transmission is effective in road having average speed around 20 to 25 kmph but during heavy traffic road condition (like Mumbai city application), average speed of vehicle comes down to 10 kmph. In heavy traffic condition (city application), operating points of motor goes into less efficiency regions which results in high energy consumption. It will also affect the regeneration.
In this study, focus is on commercial vehicle like electric buses. If we have to increase driving range, we have to optimize the energy consumption. We can address the issue of higher energy consumption in heavy traffic condition by using two speed transmission. With use of two speed transmission, motor operating points can be shifted towards higher efficiency region which will leads to less power consumption and also help to improve motor regeneration percentage.
Also, effect of motor torque requirement and battery current requirement with two speed transmission over single speed can be evaluated in Indian city driving condition. On using two speed transmission, there is leverage of increasing the restart gradeability of vehicle and also vehicle top speed. So that same powertrain configuration can be used for highway and hilly area application.