Boxster E Prototypes attract many
prospective customers
Porsche
at the Michelin Challenge Bibendum in Berlin
The two Boxster E prototypes which Porsche showed off at the Michelin
Challenge Bibendum in Berlin last week have proved to be a real
attraction to the public. At this forum for sustainable mobility, which
was staged for the eleventh time this year, representatives from
politics, industry, trade and research discussed the
environmentally-friendly mobility and vehicle concepts of the future.
The trips 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 exhibiting
the brand's characteristic combination of research and driving pleasure.
The Boxster E, with one
electric motor apiece on front and rear axle, runs on purely 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, the prototype is being used 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 are after is an understanding of the requirements facing
future products, where to go next with Porsche Intelligent Performance
and how to integrate electric vehicles into the infrastructure.
The practical trials with the
three 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 Federal Government’s “Electro-Mobility in
Model Regions” project. The Federal Ministry of Transport, Building and
Urban Development (BMVBS) is making approximately 130 million euro
available from the Federal Government’s economic stimulus package II
for eight model regions nationwide. The project is being coordinated by
NOW GmbH, the National Organisation for Hydrogen and Fuel Cell
Technology.
Thanks to its design as a
mid-engine sports car, the Porsche Boxster is the ideal vehicle
platform for conducting realistic trials with electric-drive systems.
The open-top two-seater car is very light, enabling the new components
that are 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 peculiar to the
mid-engine design.
The Boxster E is an
all-electric vehicle without any additional 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 end, 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 pleasure.
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 (62 mph) in 5.5
seconds from a standing start. Its top speed, limited to 200 km/h (124
mph) is achieved without any gear change at all – whether automatic or
manual. The two machines’ 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 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 (62 mph) in 9.8 seconds with their top speed being achieved at 150
km/h (93 mph). 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-iron-phosphate 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 (107
miles) of driving pleasure in the Boxster E with its ready-for-the-road
weight of a mere 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 are 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 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 within the vehicle. As with
the combustion engine in the production vehicle, the traction battery
is installed in the Boxster E from below and can be swapped out very
quickly if so 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 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 as well. The new brake system enables an
optimal melding of the braking forces of the electrical generators and
the mechanical brake system, the Porsche Ceramic Composite Brake
(PCCB). The electrically powered air conditioning compressor
accommodated in the front luggage compartment ensures comfortable
temperatures inside the vehicle.
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 – namely the
recovery of energy by using the electric motors as generators – can be
modified by means of the push buttons in 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 miles can be gained by switching off the
air conditioning system.
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