Materials & Design, Vol. 18, Nos. 4r6, pp. 203]209, 1997
Q 1998 Published by Elsevier Science Ltd
Printed in Great Britain. All rights reserved
0261-3069r98 $19.00 q 0.00
PII: S0261–3069(97)00049–6
Technical Report
New cars } new materials
Arno Jambor U , Matthias Beyer
Daimler-Benz AG, Adv Development Cars EP/ VF;HPC:G250,D 71059 Sindelfingen,
Germany
Received 10 July 1997; accepted 30 July 1997
Due to more demanding requirements of car occupants in relation to comfort and safety enhancing
measures, the weight of cars has been increasing, and as a result additional difficulties have been
encountered in making lighter cars. In the development of every new car there is a search for new
ways to combine the demands of the customers with reducing the weight of new cars. Further
progress in optimizing steel body design can only take place gradually. Reinforced steel or tailored
blanks are already in common use today. Even further reductions can be achieved by design in
aluminium, magnesium or plastics. At Daimler]Benz, for example, the hard-top of the SL-sports-car is
made of aluminium and the petrol tank partition panel of the SLK-roadster is made of die-cast
magnesium. Lightweight design and, consequently, fuel saving will only be successfully realized, if
proper materials are selected for appropriate parts. Q 1998 Published by Elsevier Science Ltd. All
rights reserved.
Keywords: cars; materials; design; parts
Introduction
The entire automobile industry is under considerable
pressure to reduce the fuel consumption and therefore
the emissions of their products. Over the last few
decades, traffic density has continued to grow, because
both the vehicle population and the mileage driven per
vehicle have risen considerably. At the same time, even
more demanding requirements in relation to comfort
and safety-enhancing measures have tended to increase
the weight of vehicles.
Total energy consumption of a motor ¨ ehicle
The aim of all car makers is to reduce fuel consumption. It is known that the energy consumption over the
full life cycle of a vehicle is essentially determined by
the fuel consumed during active use Ž Figure 1.. The
chart shows the percentage of energy consumed during
the life cycle of a car. This figure has to be reduced.
These reductions can be achieved by various measures
Ž Figure 2 .:
v
v
v
v
v
Disciplined driving style
Improvement of drive efficiency and tyre rolling
resistance
Improvement and optimisation of the ancillary components
Reduction of drag
Reduction of vehicle weight
Within this presentation, the remainder of this paper
U
Correspondence to Dr A. Jambor, Tel.: q49 703 1909820; fax: q49
703 1900998
Figure 1 Energy consumption during life cycle
will concentrate briefly on the effect of vehicle weight
on fuel consumption followed by examples, which show
how we can reduce the vehicle weight.
Influence of ¨ ehicle weight on fuel consumption
Road traffic generally moves at permanently changing
speeds. The influence of mass acceleration can be
clearly seen from the example of the fuel consumption
figures calculated according to the ELA ŽEuropean
Legislative Average.. Tyre rolling resistance also depends on mass Ž Figure 3 ..
The influence of vehicle mass on fuel consumption
depends more on the kind of the engine than on the
Materials & Design Volume 18 Numbers 4 / 6 1997 203
New cars } new materials: A. Jambor and M. Beyer
Figure 4 Impact of weight reduction
Figure 2 Impact on fuel consumption
Figure 3 Impact of vehicle weight on NEDC Žwith C 180.
category of the car. If we assume, that the axle-drive
ratio is adapted for same flexibility Ž60]120 km hy1 .,
the Daimler]Benz product range has the following
values according to the ELA Ž Figure 4 .
Lightweight vehicle construction
Vehicle weight factors
The overall weight of our cars is distributed about 50%
to the engine drive train and running gear and 50% to
the body. The chart shows the weight distribution of a
Mercedes-Benz C-class Ž Figure 5 ..
The increased use of lightweight materials in the
engine and drive train brings a potential weight saving
of 1]2% in relation to the gross vehicle weight. For the
running gear, the potential weight saving from the use
of these materials is about 6%. Greater potential weight
savings can be obtained in the vehicle structure, with
the body in white providing the largest contribution
through the use of new technologies or new materials.
204
Figure 5 Vehicle weight distribution Mercedes-Benz C-Class ŽC
180.
Some examples will be considered in detail in this
paper.
Lightweight design concepts in the body
The possibilities for reducing the weight of the vehicle
body start with an optimised all-steel body in
white}with a potential weight saving of about 7% Žin
relation to the body-in-white. }and span all the way to
the all-aluminium car. Here, weight reductions of
30]50% are possible. More extreme lightweight designs can only be obtained by using fibrous composite
materials Ž Figure 6 ..
Between the extremes of all-steel and all-aluminium,
there are solutions that combine steel with lightweight
materials. It should be noted that costs do not increase
in relation to the use of lightweight materials. Reducing these costs is a primary aim.
Lightweight design requirements
A lightweight design must also meet the following
Materials & Design Volume 18 Numbers 4 / 6 1997
New cars } new materials: A. Jambor and M. Beyer
Figure 8 Methods of producing a lightweight vehicle
Figure 6 Cost curve of various lightweight design concepts
Figure 7 Body shell requirements
criteria Ž Figure 7 .:
v
v
v
v
v
v
Low-cost production in high quantities
Requirements of strength, stiffness and crash resistance
Durability
Recycling
Repair concept
Acoustic properties
The requirements regarding acoustic properties,
stiffness and crash safety are now sufficiently satisfied,
as has been proved by well-known models of aluminium
construction. These questions will therefore not be
considered further in this paper.
Lightweight design methods
Vehicle weight can be reduced by an optimised design
and by lightweight materials Ž Figure 8 ..
Figure 9 Straight members in new A-class
Lightweight design shapes
Lightweight design shape means a design that is optimised for the expected load and for the material. This
can be illustrated by two examples of the recently
presented A-class Ž Figure 9 ..
The concept of this car gave us the possibility to
design the front side member straight and without
offsets, so that in the event of a frontal crash it is
optimally axial-loaded. By contrast, bent members are
always subject to bending forces, and the generated
strains have to be compensated by extra material Ž Figure 10 ..
A second example is provided by flat panels with
cambered impressing. This type of panel was used for
the floorpan of the A-class. These cambered impressions increase the impedance of the vehicle floor in the
low frequency range. In consequence, the thickness of
the fused sheets otherwise required can be reduced.
The result is a reduction of 50% in weight.
Lightweight design materials
Steel materials. Steel, as the traditional automobile material, has long since proved its worth. New highstrength sheet metal is now more and more being used
for parts exposed to high stresses.
Materials & Design Volume 18 Numbers 4 / 6 1997
205
New cars } new materials: A. Jambor and M. Beyer
can be reduced by 0.1]0.2 mm with the result of an
additional weight reduction of 5]7 kg at the E-class.
Aluminium as lightweight construction material. The
lightweight construction potential of aluminium is generally well-known, and so there is no need to explain it
in detail here. The disadvantages in terms of processing, recycling and costs are also outside the scope of
this paper. After a brief history, only the current state
of development at Daimler]Benz will be described
here.
Figure 10 Cambered panels
High-strength panels. These micro-alloyed panels enable us to reduce the panel thickness and achieve
reductions in body weight andror improve the vehicle
properties Žstrength. at reasonable costs. Modern
strength ratings of up to 540 MPa compared to 180
MPa for conventional body panels permit thinner panels in strength-relevant and crash-relevant areas Ž Figure 11..
At present, the proportion of micro-alloyed highstrength steel panels in the E-class is 20%. The increased use of these panels is at present restricted by
their limited formability. However, new steel materials
combining the qualities of higher strength and improved formability are currently being tested. These
new materials are essentially dual and triple-phase
steels. In addition to their improved formability, increased strength is a prime aim. These steels will
increase the proportion of high-strength steels in future models, and therefore the proportion of lightweight
design. One example is a tunnel panel that could not
previously be pressed in high-strength steel Ž Figure 12 ..
Continuing research into the above materials is highly
promising. It shows, that the thickness of the panels
The use of aluminium at Daimler]Benz. Our sports cars
were already making extensive use of aluminium Žand
magnesium. before the war and in the post-war years.
One representative example is the 300 SLR, a racing
car dating back to January 1956 Ž Figure 13 ..
Another example from the past, this time a standard
production model, is the 230 SL dating from 1963. This
vehicle had an inner door panel of die-cast aluminium.
The weight of the part was 6.6 kg, representing a
weight saving of about 5 kg compared to a steel construction Ž Figure 14 ..
In today’s Daimler]Benz model range, the hard-top
of the SL sports car is made of aluminium. The weight
of the roof structure has been reduced by 52%. The
customer has the advantage of a light and therefore
easily removable hard top. This all-aluminium design is
cost-intensive. The costs are about 30 DM per kg of
weight reduction compared to steel Ž Figure 15 ..
Interior parts are made of aluminium, too. For example, the structure of the new A-class seats is assembled
of aluminium parts: the seat back is a tubular space
frame, the seat rails are made of extrusion parts and
the seat cushion pan consists of a panel.
Con¨ ertible in aluminium design (study). In order to
research lightweight aluminium design at reasonable
costs using the latest technical knowledge, a lightweight
vehicle design study was carried out by Daimler]Benz
on the basis of the current Roadster SL. The development goal was to prove that all specific requirements
for the body in white}as already mentioned}could
Figure 11 Material properties of various steels
206
Materials & Design Volume 18 Numbers 4 / 6 1997
New cars } new materials: A. Jambor and M. Beyer
Figure 12 Tunnel E-class
Figure 15 SL-hardtop in aluminium
Figure 13 Mercedes-Benz 300 SLR 1956
Figure 16 Aluminium body in white SL Žstudy.
zones of the body. The following tests were performed
on the cars:
v
v
v
v
v
Figure 14 Mercedes-Benz 230 SL 1963
be met by an all-aluminium concept also for a convertible Ž Figure 16 ..
The body in white consisted of panels, extrusion
parts and die-cast components. Die-cast parts have the
advantage of high integration: there are fewer individual parts and therefore less costly joining work and an
ideal design e.g. with ribbing in the stiffness-relevant
Static and dynamic stiffness measurements
Frontal crash
Frontal offset crash at 65 km hy1 with 40% overlap
against a deformable barrier
Rear impact crash
Comprehensive road testing
The result of this study is that the high demands of
Daimler]Benz regarding passive safety, stiffness,
strength and vibration comfort can be fully satisfied in
all functional criteria}even in convertibles]by an
aluminium body designed to meet the requirements of
the material. The overall weight reduction compared to
the steel body in white of the SL including doors,
bonnet and boot lid, is 40%. Despite this remarkable
weight reduction, the costs prevented the industrialization yet Ž Figure 17 ..
Magnesium. Magnesium is an even lighter construction
material than aluminium. The use of magnesium in
sheeted panels is not feasible at present. The sheet has
to be deformed at high temperatures Žover 3008C..
Materials & Design Volume 18 Numbers 4 / 6 1997
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New cars } new materials: A. Jambor and M. Beyer
Figure 17 Aluminium body in white SL Žstudy.; crash test
Figure 19 Magnesium die-casting
Figure 18 Magnesium die-casting for structure parts
Therefore, heated tools are necessary. This makes the
process expensive. Consequently, magnesium can only
reasonably be used in die-cast production.
A well-known example of the use of magnesium for
structural components is the seat frame of the present
Roadster Žstart of production 1989.: this seat frame is
entirely made of die-cast magnesium, and the complete
seat structure weighs only about 8 kg, even though the
attachment of the restraint systems to the backrest
imposes very strict strength requirements Ž Figure 18 ..
A second standard production part made of magnesium is the petrol tank partition panel in our new SLK
sports car. The original steel panel weighed 6.7 kg and
was replaced, for weight reasons, by an aluminium
panel with the weight of 4.0 kg. Since a magnesium
die-cast version allowed a further weight reduction to
3.2 kg, the decision was made, despite the higher costs,
to introduce this lightest version in series production
Ž Figure 19 ..
Other possible applications for magnesium are in the
doors. Due to the possibility of casting thin-walled
parts Ž1]1.5 mm wall thickness ., the door inner panel
could be built of die-cast parts combined with extrusion
parts or die-cast as a single piece. A weight reduction
of 40% is imaginable Ž Figure 20 ..
One problem with the use of magnesium is the
corrosion that occurs in contact with steel or other
208
Figure 20 Door in magnesium Žstudy C-class.
materials. In this case, the materials must be kept
separate, e.g. by plastic intermediate layers or special
coatings.
Plastics. The outstanding advantages of plastics are
their low specific weight. Known or possible uses include both the outer body skin and the load-bearing
structure, mainly with the use of fiber-reinforced plastics. An example of an outer skin part at Daimler]Benz
is the plastic wing of the A-class. The material is an
unreinforced high-quality thermoplastic polyamide
blend ŽPPOrPA. Ž Figure 21..
The weight reduction compared to a steel wing is
45%. Another essential advantage is the increased customer benefit due to the reduced risk of minor damage.
The costs of the plastic wing are on a similar level to
the steel variant. Other applications for plastic outer
skin components include doors, hatches and lids. Necessary extra strength can be achieved by a two-shell
construction.
The hatch of the A-class was built using this concept.
The outer shell Žunreinforced thermoplastic. is divided
into a lower covering section and a rear roof spoiler. In
Materials & Design Volume 18 Numbers 4 / 6 1997
New cars } new materials: A. Jambor and M. Beyer
Figure 23 LK-GTR in carbon fibre
Figure 21 Wing A-class
Figure 22 Hatch A-class
the inner part made of GMT, the formability of the
material is fully exploited by the integration of the lock
fixing, hinges, rear washrwipe fixing and number plate
lamp housing Ž Figure 22 ..
The door is fully assembled as a module by the
supplier and is painted off-line. This concept offsets a
part of the higher material costs compared to steel.
However, the manufacturing costs are about 15%
higher than for the steel variant. The weight reduction
of the plastic door is 3 kg Žabout 25%..
Structural components. For load-bearing body in white
structures, only fibre-reinforced composite plastics with
appropriately oriented reinforcing fibres offer suitable
lightweight construction potential, even compared to
aluminium. The technical feasibility and advantages of
carbon fibre reinforced plastics are already well-known
from applications in aviation and space travel as well as
in motor-racing.
As long as high stiffness remains a major concern,
carbon fibres should be preferred, whereas strength
Figure 24 Crash behaviour reinforced plastic
requirements can also be very well met by glass or}this
is perhaps new}natural fibres. With this technology
we can achieve a weight reduction of 50%. Fibre reinforced plastics, depending on the structure and orientation of the fibres, not only have high stiffness and
strength but also a much higher energy absorption
potential than metals, so that in principle they can even
be used as lightweight materials in crash-relevant structural areas Ž Figures 23 and 24 ..
Conclusion
In the course of this paper, I have shown with the aid
of a few examples the possibilities that we now have for
using materials other than steel in order to reduce
vehicle weight. These methods must be improved for
future vehicles in order to meet our high demands and
specifications, whether self-imposed or laid down by
law. We must combine our efforts to attain these goals
to preserve the car itself in its full fascination.
Materials & Design Volume 18 Numbers 4 / 6 1997
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