Optimal Transmission System for Energy-Efficient Hybrid Electrified Powertrains

  • Daizy Rajput

Student thesis: Doctoral ThesisDoctor of Philosophy


Fuel consumption reduction in automotive vehicles is becoming a stringent norm across the world. Electrified powertrains provide a promising solution to fulfill this requirement.
The transmission system is the key component responsible for increasing energy
efficiency in an electrified powertrain.
The transmission system of electrified powertrains consists of a planetary gear (PG), one or two motors, battery, and an internal combustion engine. To ensure the optimal operation of the transmission system of an electrified powertrain, the optimal operationof each powertrains components is required. The PG plays a critical role by combining the output torques of different powertrain components (i.e. motors and engine) and delivering the resulting torque to the wheels. Whilst previous studies show that the number of planetary gears affects performance of hybrid electric vehicles (HEVs), there is no prior study to systematically investigate such effects on energy consumption.
This thesis quantifies the energy efficiency improvement of HEVs due to increasing the number of PGs from one to two, and from two to three. This is done by comparing the minimum energy consumption for different topologies when the rest of the powertrain components –namely electric motors, batteries and engine– are the same.
To calculate the minimum energy consumption, the thesis develops an optimal energy management strategy (EMS) for each topology to find the optimum sequence of clutch engagement and torque distribution. The minimum energy consumption of a vehicle with different number of PGs is then evaluated using the automotive simulation models (ASM) from dSpace. Results show that, for the same electric motors and engine, increasing the number of PGs from one to two and from two to three reduces energy consumption by 5% and 1.5%, respectively.
Date of Award9 May 2023
Original languageEnglish
Awarding Institution
  • Coventry University
SponsorsFEV GMBH
SupervisorMauro Innocente (Supervisor), Arash Moradinegade Dizqah (Supervisor) & Jose Martin Herreros (Supervisor)


  • Powertrains
  • HEVs
  • Electric motors
  • Automotive simulation models
  • Energy efficiency

Cite this