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Two-motor powertrain ‘can raise EV efficiencies by 15%’

25 July, 2013

An Italian vehicle transmission specialist, Oerlikon Graziano, and a UK controls specialist, Vocis Driveline, have jointly developed an electric vehicle transmission system that uses two traction motors in a compact powertrain that provides four speeds and operates with an efficiency of around 90%.

They say that the 4SED (four-speed electric drive) system can raise EV efficiencies by up to 15%, thus boosting their range, reducing the size of their batteries, or improving their performance.

The lightweight, smooth-shifting transmission is scalable, making it suitable for various types of vehicle, including urban electric cars, sportscars, hybrid four-wheel-drive vehicles, electric buses and trucks.

The system (above) resembles a dual-clutch transmission configuration, but with two motors instead of twin clutches. There are two input shafts, each driven by its own electric motor. The two motors replace the usual clutches and synchronisers, allowing the next gear to be preselected before the previous one has been disengaged, and can synchronise shaft speeds. Fewer software algorithms needed compared to a normal automated gearbox, and because there are no hydraulics, there is no need for valve control.

The motors can be installed parallel to each other, or on opposite sides of the transmission system.

An internal view of the 4SED system

“The design of the gearbox is very simple”, says Paolo Mantelli, head of Oerlikon Graziano Performance Automotive. “It is seamless, it is clutch-less, it needs no synchroniser and is truly innovative!”

Heriberto Diarte, CEO of the Oerlikon’s drive systems business, predicts that the system “will advance the development of electric vehicles”.

Oerlikon developed the mechanical design concept, while Vocis engineered the shift control system. Vocis’ work was funded partly by the Niche Vehicle Network, which is supported by the UK Government’s Technology Strategy Board.

A demonstration version of the new transmission system incorporating two 25kW motors has been fitted to an electric Mercedes Vito minibus, which Oerlikon is demonstrating to European vehicle manufacturers. It says that initial feedback has been positive.

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