Boxster E prototypes attract positive attention

The Boxster E prototypes showed by Porsche at the Michelin Challenge Bibendum in Berlin last week were a star attraction.

At the 11th staging of the forum for sustainable mobility, representatives from politics, industry, trade and research discussed environmentally-friendly mobility and vehicle concepts of the future.

Demonstrations in the electric Boxsters were in particular demand amongst the expert audience.

On a sporty circuit, the vehicles demonstrated that a Boxster with electric drive still remains a genuine Porsche in terms of driving dynamics.

In the wake of the GT3 R Hybrid, 918 Spyder and 918 RSR, the Boxster E is yet another sports car concept showing Porsche’s vision of enjoyable driving with pioneering technology.

A single Boxster E, with two electric motors – one apiece on the front and rear axle – runs on pure electric power with four-wheel drive and is equivalent to a Boxster S in terms of driving dynamics. Together with two other Boxster Es, in which an electric motor drives the rear wheels only, the three prototypes are being used to explore the everyday practicality of all-electric vehicles and how they are used, especially in terms of driving and battery charging.

The practical trials with the Boxster Es are part of the “Model Region Electro-Mobility Stuttgart” large-scale trial. The Stuttgart model region is being sponsored as part of the German Federal Government’s “Electro-Mobility in Model Regions” project.

The Boxster E is an all-electric vehicle without a combustion engine on board. Propulsion is provided by two independent electric motors with constant mesh gearboxes that act on the front and rear axles. The rear drive unit comprising motor and transmission, together with the power electronics for controlling the electric motor is located where the manual transmission and exhaust system are accommodated in the conventional Boxster.

In the front, the space vacated by the 64-litre fuel tank, now redundant, is occupied by the second drive unit. The power electronics unit in the adjacent luggage compartment serves the front axle electric motor.

The Boxster E thereby features all-wheel drive without mechanical transmission of power. To ensure maximum driving stability and traction, a central electric control unit looks after the synchronisation of the two electric motors and controls the drive torque distribution to the front and rear axle.

The two electric motors develop a total power output of 180 kW and a maximum total torque of 540 Nm at a maximum engine speed of approximately 12,000 rpm. That means that the two electric motors in tandem deliver significantly higher drive power than what is available from present day hybrid vehicles’ electric-power units.

Not only does the Boxster E’s all-electric drive produce no emissions – it also offers a completely novel form of driving enjoyment. The electric drive’s maximum torque kicks in virtually from the first turn of the engine. The Boxster E moves almost silently while at the same time developing powerful propulsion from the very outset.

The two motors enable the two-seater to sprint to 100 km/h in 5.5 seconds on its way to a 200 km/h top speed – without so much as a gear change! The two motors’ high power output offers a second advantage into the bargain: It means more recovered power is available because more energy can be recovered during braking. This increases efficiency of the drive unit.

In the case of the two other Boxster Es with rear wheel drive only, there is no front electric motor, which means that they deliver a power output of 90 kW and a rated torque of 270 Nm. They manage the sprint from a standing start to 100 km/h in 9.8 seconds with a top speed of 150 km/h.

Because all Boxster Es are comparatively quiet on the road, Porsche engineers have designed an Active Sound Design system that provides drivers with acoustic feedback as well as alerting any passersby.

Irrespective of variant, the heart of every Boxster E is manufactured by Porsche. This lithium-ronphosphate based traction battery is fitted in place of the combustion engine. Each of its cells has a nominal voltage of 3.3 V and an individual capacity of 20 Ah. Based on the NEDC, the combined energy from 440 individual cells is good for approximately 170 kilometres of driving in the Boxster E with its ready-for-the-road weight of 1,600 kg. For an overall weight of 341 kg, the battery’s energy content is 29 kWh of which for inherent physical reasons approximately 26 kWh is available for use – an outstanding performance for a battery. Its maximum power output is 240 kW, or 60 kilowatts more than the all-wheel Boxster E draws under full load. The battery and power unit components are connected to two water cooling circuits. As with the conventional power unit, the heat exchangers are accommodated behind the front air intakes.

The traction battery is charged via a charging cable. Any conventional socket can be used as an energy source. The charging port on the vehicle features an illuminated ring and as with any Porsche sports car the vehicle is recharged at the front end. The charger is accommodated at the front of the car. It converts alternating current from the socket into direct current, enabling the traction battery to store the electric energy. Its charging capacity is a maximum of 3.3 kW meaning that is takes approximately nine hours for a full charge. The charging time can, however, be reduced using a rapid charging function.

There is enough space left over for luggage in the front luggage compartment despite the electronic components; the Boxster E’s rear luggage compartment remains unchanged.

It goes without saying that all of the production models’ important safety and comfort features are replicated in the Boxster E. The new brake system enables an optimal melding of the braking forces of the electrical generators and the mechanical brake system while the electrically powered air conditioning compressor in the front luggage compartment ensures comfortable temperatures inside the Porsche.

Not only is the clutch pedal and gearshift lever absent in the Boxster E, there is no rev counter either. In its place is a special E-Power meter in the central instrument cluster display. A swing to the right indicates power call-off and to the left power recovery. Recuperation – namely the recovery of energy by using the electric motors as generators – can be modified by means of the push buttons on the steering wheel. The effect: a sort of on-demand engine brake. Otherwise, when the driver lifts his foot off the accelerator, the Boxster E simply sails on, using the moving vehicle’s kinetic energy.

Among its other functions, the instrument cluster’s right-hand TFT display acts as an intelligent range management system, displaying useful driving information: the range remaining or how many kilometres can be gained by switching off the air conditioning system.