By Jon LeSage
UK-based transmission engineering and control specialist Vocis wants to take electric vehicles in another direction, one with dual clutch transmissions. Vocis says its dual clutch transmissions provide seamless shifting and up to 15 percent improvement in EV efficiency. Vocis' DCT is currently on display in a Mercedes-Benz Vito minibus demonstration vehicle.
Many EV powertrans use a single e-machine (motor/generator). Vocis uses two smaller e-machines, each driving a separate input shaft. It's described as an eDCT (electric dual clutch transmission) and resembles a DCT configuration – but with two motors instead of twin clutches.
A multi-speed transmission offers faster acceleration and a higher top speed than a single e-machine. This improves hill climbing and pull-away performance, and its higher ratios in the transmission can provide more efficient high-speed cruising.
The multi-speed transmission can also help reduce the cost, because a smaller battery battery pack combined with the multi-speed transmission can deliver the same traveling range as a larger battery on a single-speed EV. Smaller battery, lower cost.
The eDCT was designed with modular architecture to make it pliable for a wide range of vehicle types, said Richard Taylor, technical director of Vocis Driveline Controls. The motors can be installed parallel to each other or on opposite sides of the unit, providing layout flexibility. Vocis' second-generation unit has received partial funding from the Niche Vehicle Network, a specialist car and chassis manufacturer association. It also was nominated for an SMMT Automotive Innovation Award last year.
Vocis first showed off its EV two-speed transmission during the Low Carbon Vehicle Event 2011 at Rockingham Motor Speedway in the UK. It was fitted for yet another minibus – this one a prototype electric minibus developed with powertrain supplier Zytek.