The electric drive: Urban driving fun in the fourth generation

Feb 22, 2017

The new smart electric drive makes opting into electric mobility more attractive than ever. This is because it combines the agility of the smart with local emission-free driving – the ideal match for urban mobility. With torque of 160 Newton metres immediately available the 60 kW electric car boasts exceedingly agile acceleration. The fully charged battery has sufficient power to cover approximately 160 kilometres in accordance with the New European Driving Cycle, making it ideal for urban use. With the high-performance on-board charger the smart electric drive can be charged at a household socket up to twice as fast as before – depending on the country version. The ECO mode is a particularly energy-efficient drive program. The radar-based recuperation controls the energy recovery depending on the traffic situation.

A 60 kW (81 hp) electric motor runs at the rear of the smart electric drive and transmits its power via a constant ratio to the wheels. Powerful torque of 160 Nm is immediately available from a standstill. The electric drive has a range of approximately 160 km – ideal for local emission-free mobility in urban areas. The maximum speed is electronically limited to 130 km/h to maximise the range.

The electric motor takes the form of a separately excited three-phase synchronous motor. This configuration incorporates an excitation winding on the rotor that is magnetised when current flows. The flow of energy from the high-voltage battery to the electric motor is controlled by the power electronics that are compactly interlocked with the drive unit.

Thanks to the power characteristics of the electric motor, the smart needs just one single fixed gear ratio. There is no need for any gear changing – a major advantage in dense city traffic. To reverse, the engine's direction of rotation changes. The drive is produced in Renault's plant in Clèon, Northern France.

With battery certificate: lithium-ion battery from the Daimler subsidiary Deutsche ACCUMOTIVE

The smart is equipped with a lithium-ion battery from the Daimler subsidiary Deutsche ACCUMOTIVE. The company based in Kamenz, Saxony, has been building the electric heart of the smart electric drive since 2012 (see the corresponding section for details).

The battery has capacity of 17.6 kWh and is cleverly housed in the vehicle underbody between the two axles in a safe position that is favourable for the vehicle's centre of gravity. The battery consists of 96 flat cells and the cell chemistry has been improved compared with the predecessor battery.

To strengthen customers' trust in the innovative drive technology, smart is issuing a battery certificate and therefore a service commitment for the high-voltage battery for the first time. This guarantees that the maximum energy content is not less than the specified battery capacity – over eight years and/or to a mileage of 100,000 kilometres.

Made-to-measure power output: on-board charger, fast charger, Wallbox

All smart electric drives have a powerful on-board charger as a standard feature. This enables an empty battery to be quickly charged. In the USA and the UK the charging time is 2.5 hours – half as long as for the predecessor. With the "smart control" app the charging process can be conveniently monitored from afar and functions such as intelligent charging can be controlled (see the corresponding section for details).

From the autumn of 2017 a particularly powerful 22 kW fast charger will be available as an option in Europe. This enables the smart electric drive to be charged much more quickly: in less than 45 minutes (0-80%) when local conditions allow three-phase charging.

Furthermore, smart offers a Wallbox as special equipment. This enables the vehicle to be charged with a higher charging capacity. The Wallbox must be installed by a qualified electrician and correctly connected to the mains supply.

With due regard to the given traffic situation: radar-based recuperation

As well as the basic drive program the smart electric drive driver can select the ECO mode. This is designed for a particularly efficient driving style. In addition, the maximum speed is limited, the accelerator pedal curve adjusted and the maximum recuperation level is pre-selected. Furthermore, the air conditioning control adjusts the outlet air temperature from the air vents to reduce the energy consumption.

The driver can deactivate the ECO program with the kickdown function if necessary, for example for an overtaking manoeuvre. Pushing the accelerator pedal right down activates a temporary boost. This enables maximum acceleration with defined maximum battery power if the current charge level and the temperature of the battery allow this function.

In overrun mode or when braking the vehicle's kinetic energy is converted into electrical energy – this is called recuperation. The electric motor then operates as a generator and generates braking torque on the wheels. The electrical energy generated flows back to the battery. The attainable level of energy recuperation depends on the state of the battery (charge level and temperature).

The smart electric drive models have anticipatory radar-based recuperation as a standard feature that is active in the basic drive programme. The traffic situation is monitored with a radar sensor and a recuperation level that suits the current situation is selected. The electronically controlled recuperation takes place in five levels as soon as the driver takes their foot off the accelerator pedal (overrun mode). If the road is clear coasting is activated.

In the ECO drive program the highest recuperation level is automatically set.

To save energy and further extend the range, the smart electric drive also features pre-entry climate control – see corresponding section.