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II. The first step: Halving petrol consumption
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III. The Twingo SmILE
III. The Twingo SmILE
Why has Greenpeace converted a Renault Twingo especially ?
Basically any other model could have been redesigned - from the
small car up to the limousine. Nevertheless, the Twingo offers
a comparably favourable ratio between compact external dimensions
and a spacious interior. As the most imported car in
Germany, it satisfies the needs of a family with two children
and can therefore be considered as a small and reasonable "all-round
car" for everyone.
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What is the car going to cost ?
The Twingo SmILE and all other cars built according to the SmILE
idea will not be significantly more expensive than the respective
original models. The final price naturally depends in the final
analysis upon mass production. It is important that all parts
of the Twingo SmILE as well as the necessary know-how are known
and customary in the industry. The novel and consistent combination
of consumption-reducing measures which are practically ready for
series production, is the main innovation. The manufacturing costs
of the engine should be lower in series production than those
of the previous engines, because the new engine consists of fewer
parts and the material expense is lower. Nevertheless, supercharging
costs more (independent of whether COMPREX or turbo-supercharger),
also the wheels and the wheel suspension made of aluminium. The
production facilities will not be more expensive, since the designs
are indeed different, but require in principle no new tools and
operations.
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What has been changed compared with the original Twingo ?
Twingo SmILE is lighter:
The 845 kg of the Twingo were slimmed down by the Swiss company
ESORO to the 650 kg of the Twingo SmILE - a total saving of 195
kg or 23 percent. In detail, the smaller engine including the
lighter peripherals (smaller battery, smaller radiator, lighter
exhaust system) brings around 80 kg less onto the scales. Effectively
approx. 80 kg were saved on the vehicle interior and the chassis,
e.g. by differently designed seat structures (aluminium / plastic)
as well as wheel suspensions, drum brakes, brake calliper and
rims made of light metal matched to the lower weight. With a view
towards being in series production quickly, no exotic materials
(such as titanium screws or carbon gear boxes), which in any case
would increase the price considerably, were used.
In addition, the wheel weight was reduced by using light construction
rims and special tyres and a rolling resistance value 35 percent
more favourable was achieved.
Twingo SmILE has less air resistance:
The body of the car was redesigned by the Swiss company BRM in
co-operation with the ESORO AG so that the Twingo SmILE performs
30 percent better in the wind tunnel than the original (own measurement
in the wind tunnel: cw value Twingo SmILE 0.25, cw value of the
original Twingo: 0.37).
Twingo SmILE has a smaller and more efficient engine:
The engine of the Swiss company WENKO is a supercharged two-cylinder four-stroke internal combustion engine with four-valve technology in box arrangement. A maximum torque of 75 Nm (Newton metres) results from a swept volume of 358 cm³ at 2,900 revolutions per minute.
The engine is supercharged by a dynamic pressure supercharger
which has the effect that it reaches its specifically most favourable
and economical operating conditions not at maximum speed, but
at the lower and more frequently driven speeds.
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What special features does the new engine have? Does it still
produce the same performance ?
The basic thought of the SmILE concept is that the petrol consumption of the vehicles can be clearly reduced with smaller dimensioned engines, intelligent engine technology and weight savings.
Present-day cars are too heavy and also have overdimensioned engines which utilise their maximum performance only close to maximum speed or on extreme gradients. However, engines achieve their most favourable specific fuel consumption only close to full load. In practice, they run in most cases at low load and high friction losses, far from the optimum operating point. Therefore in cars available to date, a large part of the installed power remains unused and only drives the petrol consumption upwards.
It is more advantageous (and applied in the Twingo SmILE) to drastically reduce the swept volume of the engine and to provide the torque required for acceleration or for the so-called "reserves" by supercharging. This supercharging is achieved by means of a dynamic pressure supercharger. Supercharging the combustion air in the cylinder produces a rise in performance combined with a reduction of the specific fuel consumption, so that the operating points used most frequently are shifted into the range of the highest thermal efficiency.
The engine produces at 55 bhp the same performance as the original
Twingo.
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Does the new engine fail more quickly than the old one ?
No. The WENKO engine is indeed operated more frequently in the
higher load range than conventional engines - this was, after
all, the essential trick for reducing consumption. The fear that
the engine could "blow up" early on is nevertheless
unjustified:
Because of the ingenious cooling system of the engine, higher
thermal stresses - and thus material stresses - than in conventional
engines of the same horsepower do not arise. The mean piston velocities
are in the customary range, so that no increased stresses of piston
and bearing surfaces can be expected. Due to the use of the latest
technologies in materials and surface coatings, the stability
of piston rings and cylinder bearing surfaces, for instance, is
guaranteed despite higher operating pressures in the supercharged
engine.
As a rule, the limiting factor for the life span of an car is
not the engine - most cars are scrapped before the "death
due to old age" of the engine.
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What further possibilities of optimisation are conceivable ?
At least a further 80 kg of weight could be saved by a more comprehensive
redesign of the body with fibre composite materials and replacing
the glass windows by polycarbonate. This further potential was
not made use of in view of the short-term implementation of the
SmILE concept. A smaller tank would also contribute to a further
reduction in weight.
Considerable additional potentials for reducing consumption are
to be found in a more far-reaching concept which would redesign
the entire vehicle structure: even smaller dimensioned engine;
further weight savings; improving the aerodynamics (for instance,
a cw value 15 % better could be achieved by a rear interior of
the Twingo a few percent smaller); automatic inertia utilisation
or engine switch-off systems; braking energy recovery (recuperation)
etc.
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Does the Twingo SmILE have worse or better exhaust values ?
The exhaust values of the WENKO engine in the Twingo SmILE fulfil
all standards applicable today, including the Euro II standard
applicable from 1997, and are better than in the original Twingo.
The engine concept opens up potentials for further reductions
in emission corresponding to the future requirements of the Euro
III standard (USA: ULEV standards).
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Are there reductions in comfort and performance ?
No. The interior comfort remains identical. The performance data
of the WENKO engine and the improvements in weight and aerodynamics
result in the same or better performance parameters, such as maximum
speed, elasticity and acceleration.
The correspondingly redesigned series vehicles should be equipped
with a tempomat which permits a limitation of the maximum speed
to 130 km/h (or freely selectable lower speeds), which is sensible
with regard to both transport policy and safety.
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Is the car just as safe as the old car ?
The original model, the Twingo from Renault, corresponds just
like all other licensed mass produced cars to the current state
of safety engineering. Just as the Twingo, the Twingo SmILE is
also equipped with an airbag and has lateral collision protection.
No safety relevant interventions were made in the subsequent design
changes. Every steel member with safety or rigidity functions
remains "as per Renault". The safety level of a Twingo
SmILE produced in series production will thus be comparable with
that of the original car.
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Will Renault or another car manufacturer build the Twingo SmILE ?
For the owners of the Renault Twingo, it is naturally most apparent
and especially annoying that their car manufacturer has sold them
a car which consumes twice as much petrol as would be necessary.
It is therefore conceivable that Renault would be among the first
car manufacturers to adopt the SmILE concept, or at least to build
the SmILE model itself. However, Greenpeace is calling upon not
only Renault, but all automobile manufacturers, to embrace the
SmILE concept and build SmILE cars.
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How much aluminium, PVC and other problem substances does the Twingo SmILE contain ?
No harmful substances such as CFCs or PVC were introduced into
the original Twingo in the course of the conversion.
Nevertheless, to reduce the weight of the Twingo, the original
material in the front and rear axle, wheel suspension and seat
structure was replaced by aluminium. In 1995, the average passenger
car in Europe contained 6% of aluminium (65 kg), with a rising
trend. Seven percent of the Twingo SmILE is aluminium (45 kg).
The use of aluminium is not unproblematic especially because of the high consumption of energy in the manufacture of virgin aluminium. Up to now there exist no product life-cycle analyses comparing the raw material extraction, life span, energy requirements, proportion of pollutants in production, recycling process and disposal of aluminium with conceivable substitute materials such as glass or carbon fibres. Recycled aluminium as used in the Twingo SmILE is, nevertheless, when it is processed without composite materials for example in the engine block, an almost one hundred percent reusable material with a high life, the use of which - assuming prudent recycling - is comparatively unproblematic.
Researching into more environmentally benign alternatives for
aluminium that are suitable for industry is one of the priority
tasks of the time ahead.
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