Dual Mode Electric Infinitely Variable Transmission 2004-40-0019

The Power-Split architectures for Automatic Transmissions allow the mainstream of power to pass through a high efficiency planetary gears arrangement. The variator, which controls the overall gear ratio of the transmission but usually exhibits a lower efficiency, only sees a fraction of the power coming from the ICE.

RENAULT carried out a systematic study of the possible Power-Split AT architectures in order to select the most flexible and efficient variator. Their conclusion is that an electric variator based upon two coupled electric machines, one working as a generator and the other working as a motor was probably one the of the best compromise considering all the existing technologies.

This architecture is optimised by the addition of a dual modes structure, i.e. a device enabling two different gear ratios at the variator output. This structure reduces dramatically the power that passes through the variator and thus the size of the electric machines required.

One mode is dedicated to the vehicle low speed range and the other to the higher speed range. The mode change is made at a given speed ratio. We developed and implemented a set of mechanical and control system rules that make the mode change transparent and seamless to the driver (no shocks, no vibrations, quick response).

The key advantage of such a Power-Split automatic transmission is its flexibility. Depending on the energy storage capacity fitted in between the two machines, this transmission can work as a simple Automatic Transmission (almost no energy storage), a mild hybrid transmission (limited energy storage enabling stop & start and brake & boost features) or a full-hybrid transmission (high-energy storage enabling ZEV autonomy and Off Vehicle Charging).

RENAULT is now running a comprehensive test programme on prototype vehicles on both Automatic Transmission and Mild-Hybrid versions of this infinitely variable transmission.