Transmission specialist Oerlikon Graziano, part of Oerlikon’s Drive Systems Segment, is presenting its 4SED (4 Speed Electric Drive) (earlier post) to customers around Europe. This new compact, lightweight transmission offers increased efficiency, smooth shifting and a scalable design making it suitable for a wide range of vehicle types.
The 4SED, based on Graziano’s original eDCT (electric dual clutch transmission), uses two traction motors in a very compact package which provides four speeds to allow running closer to peak efficiency. The result is an overall efficiency improvement of up to 15%, which translates into increased range or improved performance for the vehicle. The mechanical design concept was developed by Oerlikon Graziano, while the shift control system was engineered by UK controls specialist Vocis Driveline.
Oerlikon Graziano developed the 4SED transmission in anticipation of market need for increasingly efficient transmissions for low and zero emission vehicles.
The four-speed transmission uses two input shafts, each driven by its own electric motor—i.e., the concept is similar to that of a DCT but uses two motors in place of the twin clutches. One motor drives a shaft that carries first and third gears, the other drives a shaft carrying second and fourth. This allows pre-selection of the next gear before the previous one has been disengaged, using the two motors to synchronize shaft speeds so that no synchronizers are needed.
The use of the traction motors also permits a reduced set of software algorithms compared to a normal automated gearbox, and since there are no hydraulics, there is no need for valve control.
Besides improving efficiency, a multi-speed transmission leads directly to faster acceleration and a higher top speed, noted Vocis. (Earlier post.) By improving hill climbing and pull-away performance, a multi-speed transmission can increase the load carrying capacity of an electric delivery vehicle. The higher ratios in the transmission can then be specified to provide more efficient high speed cruising, enabling EVs to mix more easily with other vehicles on highways.
Further, the improved powertrain efficiency of the multi-speed transmission can also help reduce the cost of the battery pack, Vocis said. 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.
The technology is scalable to suit a wide range of different vehicle types, urban electric cars, high performance cars, hybrid 4WD applications, electric buses and trucks. It is also suitable for applications with 48V motors, allowing significant cost savings and reducing risks of high voltage, Oerlikon said.
A demonstrator has been fitted to an electric Mercedes Vito minibus and is currently touring European vehicle manufacturers to showcase its features.
The company will present more details on the 4SED at the CTI symposium in Berlin in December 2013.