Porsche has developed several Boxster E prototypes as part of the “Model Region Electro-Mobility Stuttgart” large-scale trial to explore the everyday practicality of all-electric vehicles and how they are used, especially in terms of driving and battery charging.
What the researchers at Porsche are looking for is an understanding of the requirements that will shape tomorrow’s products, the future direction of Porsche Intelligent Performance and how to integrate electric vehicles into the infrastructure.
Thanks to its mid-engine design sports, the Porsche Boxster is the ideal platform for conducting realistic trials with electric-drive systems. The two-seater is very light, enabling the electric motor, battery and high-voltage technology to be accommodated within the vehicle in a crash-proof way.
Together with the low drag, this reduces driving resistance for optimal range. Also of importance for a Porsche sports car, even one that is electrically-driven, is the high driving dynamics potential, not least as a consequence of the balanced axle-load distribution intrinsic to the mid-engine design.
The Boxster E is an all-electric vehicle without any additional combustion engine on board. On the AWD version, 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 end, the space vacated by the 64-liter fuel tank 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 therefore features all-wheel drive. To ensure maximum driving stability and traction, a central electric control unit looks after the synchronization 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 240hp and a maximum total torque of 400 lb-ft at a maximum engine speed of approximately 12000rpm. That means the two electric motors in tandem deliver significantly higher drive power than what is available from current hybrid electric power units.
As well as the all-electric drive of the Boxster E producing zero tailpipe emissions, it also offers a completely new form of Porsche driving. Maximum torque of the electric drive 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 from 0-62mph in 5.5 seconds. Its top speed, limited to124mph is achieved without any gear change – neither automatic or manual.
In the case of the RWD Boxster E, there is no front electric motor. Therefore, it delivers 120hp and 200 lb-ft. This model can sprint from a standing start to 62mph in 9.8 seconds, with a top speed of 93mph.
As all Boxster E models 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 pedestrians and other road users. As a power supply, a lithium-iron-phosphate-based traction battery is fitted in place of the combustion engine. Each of its cells has a nominal voltage of 3.3V and an individual capacity of 20Ah.
Based on the NEDC, the combined energy from 440 individual cells is good for approximately 107 miles of driving in the Boxster E, with its ready-for-the-road weight of 3525 lb. The battery and power 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 battery is anchored to the same points on the body structure as the combustion engine in the Boxster S. There are numerous advantages to this, especially in the event of a crash, because by using the same load paths as in the Boxster S, the battery is optimally retained within the vehicle while at the same time being protected from damage by the surrounding body structure thanks to its central position.
As with the combustion engine in the production car, the traction battery is installed in the Boxster E from below and can be swapped out very quickly if required. This is also facilitated by special motor sport fasteners that enable the battery to be disconnected from the cooling circuit without air getting into the system.
The traction battery is charged via a 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 ‘refuelled’ at the front end. The charger converts alternating current into direct current, enabling the traction battery to store the electric energy. Its charging capacity is a maximum of 3.3kW meaning that it 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 storage compartment despite the electronic components; the rear luggage compartment of the Boxster E remains unchanged.
Not only are 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 can be modified by means of the push buttons in the steering wheel; the effect is like an 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 miles can be gained by switching off the air conditioning system.