Electric Variable Transmission

In conventional transmissions, efficiency and performance are compromised by using fixed speed ratios. A continuously variable transmission is desired, but the costs, complexity and power ratings are not compatible with the requirements. Combining electric and mechanical drives (i.e. hybrid drive) have many advantages, but extra components and control are required. The electric variable transmission (EVT) is a hybrid transmission which combines all functionalities into one single unit. This expands the application areas and advantages of applying continuously variable hybrid drives.

The invention is a continuously variable transmission (only two rotating parts) providing full hybrid functionality. The unique construction provides more compactness than competitive technologies. As there is no mechanical link between input and output, the unit provides excellent isolation and decoupling. The main application is a hybrid transmission for powertrain applications. Additional key applications and optimisation techniques are covered by associated inventions, like systems using the EVT as a torque converter, a variator in a power split or in combination with stepped transmissions.


The EVT is suitable for use in any application where continuously variable and electric drive are combined in combination with electric power generation. This provides significant improvements in overall system efficiency and extended functionality. Example applications include:

  • Transmission in propulsion systems
  • Constant speed power take-off, with mechanical drive and electric capability
  • Combined mechanical and electric drive for auxiliaries
  • Electric clutch
  • Torque converter
  • Accessory drive
  • Electric variator

Technical Summary

The EVT is a dual-rotor electric machine based on robust induction motor technology. Due to unique design features, the EVT has a higher power density and specific power than competitive products. Low complexity due to only having two moving parts enables low maintenance and cost. As the EVT functions in power split mode, the power rating and cost of the associated power electronics is significantly reduced in comparison with a full electric-only transmission.

License - Intellectual Property

WO 03/075437
Electromechanical converter

License - Stage of Development

pilot stage

License - Proposal

licensing opportunity and research collaboration

License - TNO reference number

Licensing opportunities


Stay up to date with our latest news, activities and vacancies

TNO.nl collects and processes data in accordance with the applicable privacy regulations for an optimal user experience and marketing practices.
This data can easily be removed from your temporary profile page at any time.
You can also view our privacy statement or cookie-information.