Zytec develops electric drivetrain for Smart EV

A highly integrated electric drivetrain developed by British specialist Zytek has allowed DaimlerChrysler to introduce Europe’s first high quality, high efficiency electric commuter car.

The new smart EV (electric vehicle) provides all the safety features and dynamic ability of the standard smart fortwo, but with zero vehicle emissions and fuel costs slashed from an already class-leading Rs 3.50 per kilometre for the petrol version to just Rs 2 per kilometre for the vehicle with the new Zytek drivetrain.

All the safety features of the smart fortwo are retained, making it the only electric vehicle with two airbags, ESP, ABS, pre-tensioned seatbelts and a sturdy safety cell. Up to two hundred electric smarts will be built by Zytek at its technical centre for use in UK market trials. The vehicles will be leased to selected corporate customers from November.

The starting point was Zytek’s new, highly integrated electric drivetrain, which uses rare-earth magnet technology to deliver exceptional power density and efficiency. The brushless DC motor (which can deliver up to 125Nm peak torque and 55kW (74bhp) peak power in other applications) is calibrated to produce a smooth 120Nm peak torque and 30kW (40bhp) peak power in a package that weighs just 70kg including the motor, gearbox, inverter and control electronics.

The standard car’s cooling system is modified to control internal temperatures, using the existing front-mounted radiator with water flow assisted by an electric pump. The new drivetrain module fits neatly onto the existing engine mounting points and interfaces with all existing vehicle systems including ABS and ESP. It also provides the complete range of diagnostic information that would be expected from a high-quality conventional powertrain as well as its own range of diagnostic codes. Zytek believes that this is the only EV powertrain in production that delivers such a high level of integration with other vehicle systems.

Power is provided by a Zebra liquid sodium nickel chloride battery, mounted under the floor near the centre of the vehicle to help retain the smart’s nimble dynamics. Running at 180-310V, it has a specific power density of 194W/kg, giving a range of up to 115 kilometres. The high voltage charger, 12V charger, battery cooling fan and brake vacuum pump are installed on a purpose-designed ancillaries frame at the rear of the powertrain bay.

Because electric motors produce maximum torque throughout a large rev range (in this instance up to 12,000rpm) there is no need to change gears, so a single ratio equivalent to second has been selected. To help maximise the driving range, the maximum speed is electronically limited to 112kph. With up to 50 percent more torque than the standard 50bhp petrol car, acceleration from low speeds is brisk.

To charge the vehicle, users simply pull up within reach of a standard 13A socket and plug the charge cable into a connector behind the fuel filler. Two-and-a-half hours is sufficient to take the battery from 30 percent capacity to 80 percent and Zytek’s electronics ensure that even short charges can usefully extend the range without damaging the battery. The battery is also charged by a regenerative braking system, which works with the ABS and ESP systems to recover as much energy as possible while maintaining excellent driveability and refinement in all weather conditions.

In the cabin, a battery state of charge gauge replaces the tachometer and the gear selector has been modified to provide Drive, Neutral and Reverse. An electric element now heats the cabin air, replacing the engine hot water system. The Zytek integrated drivetrain fitted to the smart ev is the first to enter production from a range that will eventually provide vehicle manufacturers with power options from 30kW up to 100kW.