Multi-speed EV transmission to launch in demo minibus02 May 2013

Vocis is preparing to unveil an electric demonstrator vehicle fitted with the latest iteration of its novel, multi-speed, seamless-shift transmission.

The transmission engineering and control specialist has revealed that a Mercedes-Benz Vito minibus will be made available for evaluation by interested parties from the industry.

The innovative Vocis transmission uses the principles of dual clutch transmissions (DCTs) to provide seamless shifting and up to 15% improvement in electric vehicle efficiency. The second generation unit has been developed with partial funding from the Niche Vehicle Network and was shortlisted for an SMMT Automotive Innovation award in 2012.

Unlike many EV powertrains that use a single e-machine (motor/generator) the Vocis multi-speed transmission works with two smaller e-machines, each driving a separate input shaft. Described as an eDCT (electric DCT) the unique transmission resembles a DCT configuration but with two motors instead of twin clutches.

"We have used a modular architecture for the second-generation transmission, used in the demonstrator, which means the motors can be installed parallel to each other or on opposite sides of the unit," explains Richard Taylor, technical director of Vocis Driveline Controls. "This flexibility of layout, plus the scalability of the modular concept, makes the design suitable for a wide range of vehicle types."

The Vito minibus was previously fitted with the Vocis' 2SED two-speed transmission. The vehicle was subsequently modified, now accommodating a Vocis eDCT with two 25kW traction motors and the capability to accept two 35kW motors in a future upgrade.

The improved powertrain efficiency of the multi-speed transmission can help reduce the cost of the battery pack, usually the biggest single expense within an EV powertrain. A smaller battery pack, in combination with the multi-speed transmission, can provide the same vehicle range as a larger battery with only a single speed.

John Challen

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