This paper is part of an effort to reduce a vehicle’s CO2 emissions through lightweight design. The originality of the approach consists in harnessing the optimal vehicle architecture with regard to CO2 emissions. Reducing a vehicle’s weight provides an opportunity to reassess performance features like shock, noise, vibrations and road holding, thereby generating additional savings through a virtuous cycle of weight reduction. The paper sheds light on some methodological aspects used by PSA Peugeot-Citroen for designing lightweight vehicles

KRYSINSKI, Tomasz

MALBURET, François

NAUZIN, Jean-Paul

SAM;  the Arts et Métiers ParisTech open access repository

Science Arts & Métiers (SAM)
is an open access repository that collects the work of Arts et Métiers ParisTech
researchers and makes it freely available over the web where possible.
This is an author-deposited version published in: https://sam.ensam.eu
Handle ID: .http://hdl.handle.net/10985/8964
To cite this version :
François MALBURET, Tomasz KRYSINSKI, Jean-Paul NAUZIN - Lightweight design: mass in
transit - Showcase 2013 p.4 - 2012
Any correspondence concerning this service should be sent to the repository
Administrator : archiveouverte@ensam.eu
lightweight design
.com•Annual Showcase 2013
lightweight design
.com•Annual Showcase 2013
4544
The new worldwide 
accreditation cycle, the 
Worldwide Harmonized 
Light-duty Test 
Procedures (WLTP), will replace  
the current European cycle, the 
New European Driving Cycle (NEDC), 
as of 2020. It should be more 
representative of customers’ actual 
use of vehicles. In particular, it will 
include more violent acceleration/
deceleration phases and higher 
average speeds than the current 
cycle, with a view to bringing the 
measured consumption closer to that 
experienced by the customer.
The implementation of this 
new cycle will force automobile 
manufacturers to completely reassess 
the various impacts related to 
consumption. While the influence 
of some major factors in the NEDC 
cycle (downsizing or electrification 
of components, etc.) will be more 
limited in the WLTP cycle, the 
impact of factors such as weight will 
increase.
Figure 1 shows that the weight of 
vehicles has increased substantially 
over the past 15 years, a trend that is 
common to all manufacturers.
This change is due to a number of 
factors which, when listed in order 
of importance, are as follows: 40% 
due to passive safety; 15% due to the 
development of vehicle equipment; 
15% due to improved soundproofing, 
as well as safety-related structural 
reinforcements; increased vehicle 
size; pollution reduction systems; 
and increased weight of other 
components such as suspension 
systems, brakes and gearbox systems, 
in order to offset the increased loads 
on vehicle axles.
The impact of weight on 
consumption has been shown 
in a statistical study carried out 
on 33 recent diesel vehicles. It 
roughly indicates that an additional 
consumption of approximately 
0.5 l/100km can be expected 
per 100kg of extra weight. In 
practice, this is far more complex, 
as consumption depends on more 
than weight alone. Factors related 
to the vehicle’s aerodynamic drag 
as well as its expected performance, 
which determines the size of the 
powertrain, must also be factored in.
Reducing consumption involves 
much more than engine development. 
All consumption sources – including 
tire rolling resistance and vehicle 
weight – as well as their reduction 
potentials, need to be assessed 
through a systematic, physical 
approach. It is also very important 
to account for the way in which the 
various actions are interconnected in 
order to achieve the best result.
Designing a lightweight vehicle 
There are many ways to reduce 
vehicle CO2 emissions by reducing 
weight: through direct effects (e.g. 
reducing the weight of components 
by using lighter materials) and 
indirect effects (virtuous cycle 
generated by initial weight savings).
In terms of direct effects, 
understanding the way in which 
weight and architecture are 
interconnected is key when it  
comes to lightweight vehicle design. 
Vehicles are comprised of ‘hard’ 
items such as the engine and brakes, 
which constitute a mostly non-
compressible weight when changing 
the vehicle’s dimensions. Therefore, 
modifying the vehicle’s dimensions 
will not have a significant impact  
on the weight of its components. 
Put simply, on a constant 
equipment basis, the variation in 
weight from one vehicle to another 
is primarily related to the variation 
in the vehicle’s dimensions. This 
is referred to as downsizing, or 
architecture fine-tuning, which 
ensures ample interior space by 
reducing the dimensions that 
are relevant for weight reduction 
purposes. To do this, the vehicle’s 
weight is broken down into five 
parts, as shown in Figure 2. The 
statistical data on the same segment 
provides an average data for each 
segment, which varies according to 
the technologies used.
The value of these gradients is 
empirical and is used for pre-project 
calculations. 
Mass in transit
TOMASZ KRYSINSKI AND JEAN-PAUL NAUZIN (PSA PEUGEOT CITROËN) AND  
FRANÇOIS MALBURET (ARTS ET MÉTIERS PARISTECH) OFFER SOME FACTORS FOR 
CONSIDERATION WHEN DESIGNING A LIGHTWEIGHT VEHICLE
“Decreasing the 
vehicle’s weight 
directly decreases 
the energy  
that has to  
be dissipated 
proportionately 
and therefore 
makes it possible 
to use smaller 
brakes”
Rolling resistance
Tires play a complex role in reducing 
fuel consumption, as they affect 
rolling resistance, aerodynamics, and 
the general architecture (Figure 3).
Rolling resistance is directly 
related to the wheels’ tire 
geometrical data. The larger a 
vehicle’s wheels are, the lower its 
friction coefficient is. 
With the f function dependent on 
the size of the tire and the technology 
used
The design of the tread layer can 
reduce the aerodynamic drag by a 
few percent. The design of the tread 
layer and the outer sidewall can 
reduce the air surface and optimize 
the airflow around the tire. When 
modeling in the preliminary vehicle 
design phase to define the impact 
of architecture on consumption, the 
effects of the aerodynamic pressure 
zones around the wheel area are 
neglected.
More generally, reducing 
consumption involves finding a 
compromise between the various 
factors related to aerodynamics, 
rolling resistance, and weight.
For example, increasing the wheels’ 
diameter increases the vehicle’s 
weight while maintaining the same 
interior space; reduces the rolling 
resistance coefficient; and increases 
the aerodynamic drag.
Overall, increasing the wheels’ 
diameter increases the vehicle’s 
consumption.
New materials and technologies
Once the vehicle’s architecture has 
been determined, weight can  
also be reduced by introducing 
new materials and integrating 
components and functions in the 
same system. Figure 4 shows the 
weight proportions of the various 
subsystems of a vehicle.
A classical way to reduce vehicle 
weight involves the use of lighter 
materials such as aluminum, 
magnesium, plastic, or carbon fiber, 
as well as steel alloys. As mentioned 
above, reducing a vehicle’s weight 
by 100kg results in savings of 0.5 
l/100km. However, the large-scale 
distribution of these lightweight 
materials is not developed widely 
enough and is still too limited to 
high-end cars.
The use of new technologies can 
contribute to reducing vehicle weight 
directly. This can be the case by 
combining functions, optimizing 
components, developing intelligent 
solutions, or integrating functions 
such as third-generation bearings, 
one-piece parts, future mechatronics 
systems, or using nanotechnologies 
over the longer term. Given  
the large number of sensors and 
electronics in passenger vehicles, 
nanotechnologies have a strong 
potential to miniaturize and transfer 
data. A major hurdle is producing 
these components and integrating 
them into production lines, as well as 
recycling them.
Virtuous cycles
Following an initial weight-reduction 
phase by optimizing the architecture 
and choice of materials, a second 
weight-reduction phase can be 
obtained by assessing the effects of 
the first weight-reduction phase.
FIGURE 3: THE TIRE’S INFLUENCE  
IN SAVING VEHICLE WEIGHT
FIGURE 4: VEHICLE WEIGHT  
SUBSYSTEM CONTRIBUTIONS
FIGURE 5: LOAD TRANSFER DURING 
BRAKING
The first weight-reduction phase 
has effects on subsystems’ loads. Each 
subsystem can then be optimized, 
thereby further reducing the weight 
of the overall structure.
Reducing a vehicle’s weight and 
the inter-structure forces also has an 
effect on the vehicle’s performance, 
which can be broken down into three 
main groups – impact, rigidity, and 
resistance. Each of these groups is 
affected by a set of performances 
that has a bearing on weight. 
These performances need to be 
taken into account when optimizing 
each subsystem. This will often result 
in finding a compromise.
The downsizing of brake system 
components is one example of a 
virtuous effect. The required braking 
power at time t is expressed by:
If we assume that the power losses 
related to rolling and aerodynamic 
forces are insignificant, as well as 
the engine braking action, then we 
can approximate the braking power 
output by:
FIGURE 1: CHANGE IN VEHICLE 
WEIGHT OVER THE PAST 30 YEARS
FIGURE 2: SIMPLIFIED MODELING  
OF THE VEHICLE’S WEIGHT BASED  
ON GEOMETRIC PARAMETERS
1
2
3 4
5
.com•Annual Showcase 2013.com•Annual Showcase 2013
46 lightweight design
The analysis of forces during 
braking shows that the rear end has a 
tendency to underload, and the front 
end on the contrary to overload. 
When we brake, we tend not to brake 
in a straight line, so a force is applied 
to the side of the tire. A lateral force 
develops in the contact area and the 
tire moves frontward at an angle a, 
called slip angle, with the direction 
of heading (Figure 6). This is how a 
tire’s drift rigidity can be defined.
The approach is made more 
complex by the non-linear behavior 
of the suspension and tires (Figure 7).
If the load discharged on the 
rear wheels becomes too little, 
the vehicle’s performance will be 
affected. When braking, the load 
transfer is closely related to the 
longitudinal deceleration, the 
vehicle’s speed, and the transverse 
acceleration (braking in a curve). 
Thus it is demonstrated, based on 
the distribution of these forces, 
that there can be potential risks 
of instability from certain vehicle 
speeds based on the deceleration 
(Figure 8).
This problem must be taken into 
account during the preliminary 
design phase for lightweight vehicles 
by modifying the position of the 
center of gravity, paying close 
attention to the front/rear weight 
distribution, or modifying the 
aerodynamic coefficient to hold 
the vehicle to the ground.
Material world
Magneti Marelli has been working  
on prototype composite suspension  
components for some years now, writes  
Graham Heeps. Having realized a mass- 
production-feasible, crash-safe, reinforced 
composite suspension arm that reduces 
component weight from around 1.5kg  
for an ultralight steel version to no more 
than 0.85kg, the firm’s next target is to 
investigate the use of basalt- or glass-fiber 
to bring the cost down. The carbon-fiber 
version comes in at around five times the 
cost of the steel alternative.
“In the next few years composite  
materials will play a very important  
role in automotive structural and safety 
components,” says Piero Monchiero,  
suspension R&D manager at Magneti  
Marelli. “We are starting to understand 
which are the right technologies and which 
will be the right technical solutions to  
develop our parts and components with this 
kind of material.
“We started with carbon fiber but along 
the way we’ve come to understand that it’s 
probably not necessary. Basalt and glass-
fiber will probably be good enough for  
conventional vehicles. The cost of glass and 
basalt is very acceptable but it is necessary 
to develop the technology a little bit to  
verify their reliability over the long term. 
Our parts have a long life, 15-20 years, so 
we have to verify their safety. But I think 
that we are near to having good, light  
materials [for suspension parts] using 
composites.”
Magneti Marelli is studying the potential 
for composite knuckles and is also working 
on a front subframe made from a composite 
material. The latter probably won’t need 
reinforcement from a ductile material,  
according to Monchiero.
“For components like the arms,  
which you have to sacrifice under crash 
conditions, yes it’s necessary,” he says. “But 
according to our first level of verification 
for subframes, it’s probably not. These  
components have to be stiffer, more  
resistant, so it probably isn’t necessary to 
use a hybrid [material] solution.”
The rapid pace of development in  
this area provides a real opportunity for 
innovation, Monchiero believes. “The base 
plastics materials are being developed very 
quickly. I see that when I talk to suppliers 
of plastic materials over the course of a few 
months, they tell me that they now have 
new materials available. For example, when 
we started work on the composite arm, we 
used a thermoplastic material because at 
the time, this was the plastic material with  
the fastest curing time. But now thermoset 
materials are also achieving very short cure 
times, meaning that each operation needs 
less than one minute rather than the 10  
or 15 minutes of before. We had to change 
to using thermoset material because the 
technology had developed so much.”
The energy dissipated over braking 
time T is given by the equation:
For example, a 1,400kg vehicle 
moving at 120km/h has to dissipate 
776kJ of energy, which gives an 
average power of 141kW for a braking 
time of 5.5 seconds (deceleration 
of 0.6g). This energy that has to 
be dissipated has an impact on 
the force that has to be created 
inside the brakes. Decreasing the 
vehicle’s weight directly decreases 
the energy that has to be dissipated 
proportionately and therefore  
makes it possible to use smaller 
brakes. The relationship between  
the energy dissipated and the  
size of brakes (and therefore  
their weight) is not linear or 
continuous. For example, changing 
from 283 x 26 front disc brakes with 
caliper 60 to 266 x 22 front discs 
with caliper 57, related to a 150kg 
reduction in gross vehicle weight, 
saves 5.7kg for vehicles in the C 
segment.
Weight reduction measures such  
as this can create problems, however, 
as the example of high-speed braking 
shows. A vehicle at a standstill has 
an initial load distribution on the 
various wheels. When rolling, and 
especially in braking situations, 
the load on each tire will vary. This 
results in an additive or subtractive 
force based on the stress placed on 
the vehicle. A number of parameters 
influence this weight transfer 
including the vehicle’s weight,  
the position of the center of  
gravity, the wheelbase, the width  
of the road, the downforces, and the 
tires’ performance. 
A D M A
E x p e r t i s e i n
G P S a n d I n e r t i a l
M e t r o l o g y
Inertial / GPS System for
Vehicle Dynamics Testing
GPS synchronized
easy to use
fast set-up
low data latency
· Vehicle Dynamics Testing
· Functional Safety Testing
· Adjustment of Chassis Systems
· Comfort Analysis
· Tyre Testing
· Deceleration / Acceleration Testing
· Road Survey and Monitoring
· Highly Precise Positioning
· Verification of Simulation Models
· Steering Robot Guidance
· Driver Assistance Systems Testing
GeneSys Elektronik GmbH
www.genesys-adma.de
77656 Offenburg · Germany
Tel.  +49 781 / 969279-0
Tel. USA  +1 401-284-3750
adma@genesys-offenburg.de
GeneSys
Elektronik GmbH
FIGURE 6: SLIP ANGLE 
AND RESPONSE TO A 
LATERAL FORCE
FIGURE 7: TIRE’S DRIFT  
RIGIDITY BASED ON 
THE APPLIED LOAD
FIGURE 8: DIAGRAM OF  
STABILITY DURING 
THE BRAKING PHASE
6
7
8


English

Lightweight design: mass in transit

SAM : Science Arts et Métiers

Science Arts & Métiers (SAM)is an open access repository that collects the work of Arts et Métiers Institute ofTechnology researchers and makes it freely available over the web where possible.This is an author-deposited version published in: https://sam.ensam.euHandle ID: .http://hdl.handle.net/10985/8964To cite this version :François MALBURET, Tomasz KRYSINSKI, Jean-Paul NAUZIN - Lightweight design: mass intransit - Showcase 2013 p.4 - 2012Any correspondence concerning this service should be sent to the repositoryAdministrator : archiveouverte@ensam.eulightweight design.com•Annual Showcase 2013lightweight design.com•Annual Showcase 20134544The new worldwide accreditation cycle, the Worldwide Harmonized Light-duty Test Procedures (WLTP), will replace  the current European cycle, the New European Driving Cycle (NEDC), as of 2020. It should be more representative of customers’ actual use of vehicles. In particular, it will include more violent acceleration/deceleration phases and higher average speeds than the current cycle, with a view to bringing the measured consumption closer to that experienced by the customer.The implementation of this new cycle will force automobile manufacturers to completely reassess the various impacts related to consumption. While the influence of some major factors in the NEDC cycle (downsizing or electrification of components, etc.) will be more limited in the WLTP cycle, the impact of factors such as weight will increase.Figure 1 shows that the weight of vehicles has increased substantially over the past 15 years, a trend that is common to all manufacturers.This change is due to a number of factors which, when listed in order of importance, are as follows: 40% due to passive safety; 15% due to the development of vehicle equipment; 15% due to improved soundproofing, as well as safety-related structural reinforcements; increased vehicle size; pollution reduction systems; and increased weight of other components such as suspension systems, brakes and gearbox systems, in order to offset the increased loads on vehicle axles.The impact of weight on consumption has been shown in a statistical study carried out on 33 recent diesel vehicles. It roughly indicates that an additional consumption of approximately 0.5 l/100km can be expected per 100kg of extra weight. In practice, this is far more complex, as consumption depends on more than weight alone. Factors related to the vehicle’s aerodynamic drag as well as its expected performance, which determines the size of the powertrain, must also be factored in.Reducing consumption involves much more than engine development. All consumption sources – including tire rolling resistance and vehicle weight – as well as their reduction potentials, need to be assessed through a systematic, physical approach. It is also very important to account for the way in which the various actions are interconnected in order to achieve the best result.Designing a lightweight vehicle There are many ways to reduce vehicle CO2 emissions by reducing weight: through direct effects (e.g. reducing the weight of components by using lighter materials) and indirect effects (virtuous cycle generated by initial weight savings).In terms of direct effects, understanding the way in which weight and architecture are interconnected is key when it  comes to lightweight vehicle design. Vehicles are comprised of ‘hard’ items such as the engine and brakes, which constitute a mostly non-compressible weight when changing the vehicle’s dimensions. Therefore, modifying the vehicle’s dimensions will not have a significant impact  on the weight of its components. Put simply, on a constant equipment basis, the variation in weight from one vehicle to another is primarily related to the variation in the vehicle’s dimensions. This is referred to as downsizing, or architecture fine-tuning, which ensures ample interior space by reducing the dimensions that are relevant for weight reduction purposes. To do this, the vehicle’s weight is broken down into five parts, as shown in Figure 2. The statistical data on the same segment provides an average data for each segment, which varies according to the technologies used.The value of these gradients is empirical and is used for pre-project calculations. Mass in transitTOMASZ KRYSINSKI AND JEAN-PAUL NAUZIN (PSA PEUGEOT CITROËN) AND  FRANÇOIS MALBURET (ARTS ET MÉTIERS PARISTECH) OFFER SOME FACTORS FOR CONSIDERATION WHEN DESIGNING A LIGHTWEIGHT VEHICLE“Decreasing the vehicle’s weight directly decreases the energy  that has to  be dissipated proportionately and therefore makes it possible to use smaller brakes”Rolling resistanceTires play a complex role in reducing fuel consumption, as they affect rolling resistance, aerodynamics, and the general architecture (Figure 3).Rolling resistance is directly related to the wheels’ tire geometrical data. The larger a vehicle’s wheels are, the lower its friction coefficient is. With the f function dependent on the size of the tire and the technology usedThe design of the tread layer can reduce the aerodynamic drag by a few percent. The design of the tread layer and the outer sidewall can reduce the air surface and optimize the airflow around the tire. When modeling in the preliminary vehicle design phase to define the impact of architecture on consumption, the effects of the aerodynamic pressure zones around the wheel area are neglected.More generally, reducing consumption involves finding a compromise between the various factors related to aerodynamics, rolling resistance, and weight.For example, increasing the wheels’ diameter increases the vehicle’s weight while maintaining the same interior space; reduces the rolling resistance coefficient; and increases the aerodynamic drag.Overall, increasing the wheels’ diameter increases the vehicle’s consumption.New materials and technologiesOnce the vehicle’s architecture has been determined, weight can  also be reduced by introducing new materials and integrating components and functions in the same system. Figure 4 shows the weight proportions of the various subsystems of a vehicle.A classical way to reduce vehicle weight involves the use of lighter materials such as aluminum, magnesium, plastic, or carbon fiber, as well as steel alloys. As mentioned above, reducing a vehicle’s weight by 100kg results in savings of 0.5 l/100km. However, the large-scale distribution of these lightweight materials is not developed widely enough and is still too limited to high-end cars.The use of new technologies can contribute to reducing vehicle weight directly. This can be the case by combining functions, optimizing components, developing intelligent solutions, or integrating functions such as third-generation bearings, one-piece parts, future mechatronics systems, or using nanotechnologies over the longer term. Given  the large number of sensors and electronics in passenger vehicles, nanotechnologies have a strong potential to miniaturize and transfer data. A major hurdle is producing these components and integrating them into production lines, as well as recycling them.Virtuous cyclesFollowing an initial weight-reduction phase by optimizing the architecture and choice of materials, a second weight-reduction phase can be obtained by assessing the effects of the first weight-reduction phase.FIGURE 3: THE TIRE’S INFLUENCE  IN SAVING VEHICLE WEIGHTFIGURE 4: VEHICLE WEIGHT  SUBSYSTEM CONTRIBUTIONSFIGURE 5: LOAD TRANSFER DURING BRAKINGThe first weight-reduction phase has effects on subsystems’ loads. Each subsystem can then be optimized, thereby further reducing the weight of the overall structure.Reducing a vehicle’s weight and the inter-structure forces also has an effect on the vehicle’s performance, which can be broken down into three main groups – impact, rigidity, and resistance. Each of these groups is affected by a set of performances that has a bearing on weight. These performances need to be taken into account when optimizing each subsystem. This will often result in finding a compromise.The downsizing of brake system components is one example of a virtuous effect. The required braking power at time t is expressed by:If we assume that the power losses related to rolling and aerodynamic forces are insignificant, as well as the engine braking action, then we can approximate the braking power output by:FIGURE 1: CHANGE IN VEHICLE WEIGHT OVER THE PAST 30 YEARSFIGURE 2: SIMPLIFIED MODELING  OF THE VEHICLE’S WEIGHT BASED  ON GEOMETRIC PARAMETERS123 45.com•Annual Showcase 2013.com•Annual Showcase 201346 lightweight designThe analysis of forces during braking shows that the rear end has a tendency to underload, and the front end on the contrary to overload. When we brake, we tend not to brake in a straight line, so a force is applied to the side of the tire. A lateral force develops in the contact area and the tire moves frontward at an angle a, called slip angle, with the direction of heading (Figure 6). This is how a tire’s drift rigidity can be defined.The approach is made more complex by the non-linear behavior of the suspension and tires (Figure 7).If the load discharged on the rear wheels becomes too little, the vehicle’s performance will be affected. When braking, the load transfer is closely related to the longitudinal deceleration, the vehicle’s speed, and the transverse acceleration (braking in a curve). Thus it is demonstrated, based on the distribution of these forces, that there can be potential risks of instability from certain vehicle speeds based on the deceleration (Figure 8).This problem must be taken into account during the preliminary design phase for lightweight vehicles by modifying the position of the center of gravity, paying close attention to the front/rear weight distribution, or modifying the aerodynamic coefficient to hold the vehicle to the ground.Material worldMagneti Marelli has been working  on prototype composite suspension  components for some years now, writes  Graham Heeps. Having realized a mass- production-feasible, crash-safe, reinforced composite suspension arm that reduces component weight from around 1.5kg  for an ultralight steel version to no more than 0.85kg, the firm’s next target is to investigate the use of basalt- or glass-fiber to bring the cost down. The carbon-fiber version comes in at around five times the cost of the steel alternative.“In the next few years composite  materials will play a very important  role in automotive structural and safety components,” says Piero Monchiero,  suspension R&D manager at Magneti  Marelli. “We are starting to understand which are the right technologies and which will be the right technical solutions to  develop our parts and components with this kind of material.“We started with carbon fiber but along the way we’ve come to understand that it’s probably not necessary. Basalt and glass-fiber will probably be good enough for  conventional vehicles. The cost of glass and basalt is very acceptable but it is necessary to develop the technology a little bit to  verify their reliability over the long term. Our parts have a long life, 15-20 years, so we have to verify their safety. But I think that we are near to having good, light  materials [for suspension parts] using composites.”Magneti Marelli is studying the potential for composite knuckles and is also working on a front subframe made from a composite material. The latter probably won’t need reinforcement from a ductile material,  according to Monchiero.“For components like the arms,  which you have to sacrifice under crash conditions, yes it’s necessary,” he says. “But according to our first level of verification for subframes, it’s probably not. These  components have to be stiffer, more  resistant, so it probably isn’t necessary to use a hybrid [material] solution.”The rapid pace of development in  this area provides a real opportunity for innovation, Monchiero believes. “The base plastics materials are being developed very quickly. I see that when I talk to suppliers of plastic materials over the course of a few months, they tell me that they now have new materials available. For example, when we started work on the composite arm, we used a thermoplastic material because at the time, this was the plastic material with  the fastest curing time. But now thermoset materials are also achieving very short cure times, meaning that each operation needs less than one minute rather than the 10  or 15 minutes of before. We had to change to using thermoset material because the technology had developed so much.”The energy dissipated over braking time T is given by the equation:For example, a 1,400kg vehicle moving at 120km/h has to dissipate 776kJ of energy, which gives an average power of 141kW for a braking time of 5.5 seconds (deceleration of 0.6g). This energy that has to be dissipated has an impact on the force that has to be created inside the brakes. Decreasing the vehicle’s weight directly decreases the energy that has to be dissipated proportionately and therefore  makes it possible to use smaller brakes. The relationship between  the energy dissipated and the  size of brakes (and therefore  their weight) is not linear or continuous. For example, changing from 283 x 26 front disc brakes with caliper 60 to 266 x 22 front discs with caliper 57, related to a 150kg reduction in gross vehicle weight, saves 5.7kg for vehicles in the C segment.Weight reduction measures such  as this can create problems, however, as the example of high-speed braking shows. A vehicle at a standstill has an initial load distribution on the various wheels. When rolling, and especially in braking situations, the load on each tire will vary. This results in an additive or subtractive force based on the stress placed on the vehicle. A number of parameters influence this weight transfer including the vehicle’s weight,  the position of the center of  gravity, the wheelbase, the width  of the road, the downforces, and the tires’ performance. A D M AE x p e r t i s e i nG P S a n d I n e r t i a lM e t r o l o g yInertial / GPS System forVehicle Dynamics TestingGPS synchronizedeasy to usefast set-uplow data latency· Vehicle Dynamics Testing· Functional Safety Testing· Adjustment of Chassis Systems· Comfort Analysis· Tyre Testing· Deceleration / Acceleration Testing· Road Survey and Monitoring· Highly Precise Positioning· Verification of Simulation Models· Steering Robot Guidance· Driver Assistance Systems TestingGeneSys Elektronik GmbHwww.genesys-adma.de77656 Offenburg · GermanyTel.  +49 781 / 969279-0Tel. USA  +1 401-284-3750adma@genesys-offenburg.deGeneSysElektronik GmbHFIGURE 6: SLIP ANGLE AND RESPONSE TO A LATERAL FORCEFIGURE 7: TIRE’S DRIFT  RIGIDITY BASED ON THE APPLIED LOADFIGURE 8: DIAGRAM OF  STABILITY DURING THE BRAKING PHASE678

Name not available

Science Arts & Métiers (SAM)is an open access repository that collects the work of Arts et Métiers ParisTechresearchers and makes it freely available over the web where possible.This is an author-deposited version published in: http://sam.ensam.euHandle ID: .http://hdl.handle.net/10985/8964To cite this version :François MALBURET, Tomasz KRYSINSKI, Jean-Paul NAUZIN - Lightweight design: mass intransit - Showcase 2013 p.4 - 2012Any correspondence concerning this service should be sent to the repositoryAdministrator : archiveouverte@ensam.eulightweight design.com•Annual Showcase 2013lightweight design.com•Annual Showcase 20134544The new worldwide accreditation cycle, the Worldwide Harmonized Light-duty Test Procedures (WLTP), will replace  the current European cycle, the New European Driving Cycle (NEDC), as of 2020. It should be more representative of customers’ actual use of vehicles. In particular, it will include more violent acceleration/deceleration phases and higher average speeds than the current cycle, with a view to bringing the measured consumption closer to that experienced by the customer.The implementation of this new cycle will force automobile manufacturers to completely reassess the various impacts related to consumption. While the influence of some major factors in the NEDC cycle (downsizing or electrification of components, etc.) will be more limited in the WLTP cycle, the impact of factors such as weight will increase.Figure 1 shows that the weight of vehicles has increased substantially over the past 15 years, a trend that is common to all manufacturers.This change is due to a number of factors which, when listed in order of importance, are as follows: 40% due to passive safety; 15% due to the development of vehicle equipment; 15% due to improved soundproofing, as well as safety-related structural reinforcements; increased vehicle size; pollution reduction systems; and increased weight of other components such as suspension systems, brakes and gearbox systems, in order to offset the increased loads on vehicle axles.The impact of weight on consumption has been shown in a statistical study carried out on 33 recent diesel vehicles. It roughly indicates that an additional consumption of approximately 0.5 l/100km can be expected per 100kg of extra weight. In practice, this is far more complex, as consumption depends on more than weight alone. Factors related to the vehicle’s aerodynamic drag as well as its expected performance, which determines the size of the powertrain, must also be factored in.Reducing consumption involves much more than engine development. All consumption sources – including tire rolling resistance and vehicle weight – as well as their reduction potentials, need to be assessed through a systematic, physical approach. It is also very important to account for the way in which the various actions are interconnected in order to achieve the best result.Designing a lightweight vehicle There are many ways to reduce vehicle CO2 emissions by reducing weight: through direct effects (e.g. reducing the weight of components by using lighter materials) and indirect effects (virtuous cycle generated by initial weight savings).In terms of direct effects, understanding the way in which weight and architecture are interconnected is key when it  comes to lightweight vehicle design. Vehicles are comprised of ‘hard’ items such as the engine and brakes, which constitute a mostly non-compressible weight when changing the vehicle’s dimensions. Therefore, modifying the vehicle’s dimensions will not have a significant impact  on the weight of its components. Put simply, on a constant equipment basis, the variation in weight from one vehicle to another is primarily related to the variation in the vehicle’s dimensions. This is referred to as downsizing, or architecture fine-tuning, which ensures ample interior space by reducing the dimensions that are relevant for weight reduction purposes. To do this, the vehicle’s weight is broken down into five parts, as shown in Figure 2. The statistical data on the same segment provides an average data for each segment, which varies according to the technologies used.The value of these gradients is empirical and is used for pre-project calculations. Mass in transitTOMASZ KRYSINSKI AND JEAN-PAUL NAUZIN (PSA PEUGEOT CITROËN) AND  FRANÇOIS MALBURET (ARTS ET MÉTIERS PARISTECH) OFFER SOME FACTORS FOR CONSIDERATION WHEN DESIGNING A LIGHTWEIGHT VEHICLE“Decreasing the vehicle’s weight directly decreases the energy  that has to  be dissipated proportionately and therefore makes it possible to use smaller brakes”Rolling resistanceTires play a complex role in reducing fuel consumption, as they affect rolling resistance, aerodynamics, and the general architecture (Figure 3).Rolling resistance is directly related to the wheels’ tire geometrical data. The larger a vehicle’s wheels are, the lower its friction coefficient is. With the f function dependent on the size of the tire and the technology usedThe design of the tread layer can reduce the aerodynamic drag by a few percent. The design of the tread layer and the outer sidewall can reduce the air surface and optimize the airflow around the tire. When modeling in the preliminary vehicle design phase to define the impact of architecture on consumption, the effects of the aerodynamic pressure zones around the wheel area are neglected.More generally, reducing consumption involves finding a compromise between the various factors related to aerodynamics, rolling resistance, and weight.For example, increasing the wheels’ diameter increases the vehicle’s weight while maintaining the same interior space; reduces the rolling resistance coefficient; and increases the aerodynamic drag.Overall, increasing the wheels’ diameter increases the vehicle’s consumption.New materials and technologiesOnce the vehicle’s architecture has been determined, weight can  also be reduced by introducing new materials and integrating components and functions in the same system. Figure 4 shows the weight proportions of the various subsystems of a vehicle.A classical way to reduce vehicle weight involves the use of lighter materials such as aluminum, magnesium, plastic, or carbon fiber, as well as steel alloys. As mentioned above, reducing a vehicle’s weight by 100kg results in savings of 0.5 l/100km. However, the large-scale distribution of these lightweight materials is not developed widely enough and is still too limited to high-end cars.The use of new technologies can contribute to reducing vehicle weight directly. This can be the case by combining functions, optimizing components, developing intelligent solutions, or integrating functions such as third-generation bearings, one-piece parts, future mechatronics systems, or using nanotechnologies over the longer term. Given  the large number of sensors and electronics in passenger vehicles, nanotechnologies have a strong potential to miniaturize and transfer data. A major hurdle is producing these components and integrating them into production lines, as well as recycling them.Virtuous cyclesFollowing an initial weight-reduction phase by optimizing the architecture and choice of materials, a second weight-reduction phase can be obtained by assessing the effects of the first weight-reduction phase.FIGURE 3: THE TIRE’S INFLUENCE  IN SAVING VEHICLE WEIGHTFIGURE 4: VEHICLE WEIGHT  SUBSYSTEM CONTRIBUTIONSFIGURE 5: LOAD TRANSFER DURING BRAKINGThe first weight-reduction phase has effects on subsystems’ loads. Each subsystem can then be optimized, thereby further reducing the weight of the overall structure.Reducing a vehicle’s weight and the inter-structure forces also has an effect on the vehicle’s performance, which can be broken down into three main groups – impact, rigidity, and resistance. Each of these groups is affected by a set of performances that has a bearing on weight. These performances need to be taken into account when optimizing each subsystem. This will often result in finding a compromise.The downsizing of brake system components is one example of a virtuous effect. The required braking power at time t is expressed by:If we assume that the power losses related to rolling and aerodynamic forces are insignificant, as well as the engine braking action, then we can approximate the braking power output by:FIGURE 1: CHANGE IN VEHICLE WEIGHT OVER THE PAST 30 YEARSFIGURE 2: SIMPLIFIED MODELING  OF THE VEHICLE’S WEIGHT BASED  ON GEOMETRIC PARAMETERS123 45.com•Annual Showcase 2013.com•Annual Showcase 201346 lightweight designThe analysis of forces during braking shows that the rear end has a tendency to underload, and the front end on the contrary to overload. When we brake, we tend not to brake in a straight line, so a force is applied to the side of the tire. A lateral force develops in the contact area and the tire moves frontward at an angle a, called slip angle, with the direction of heading (Figure 6). This is how a tire’s drift rigidity can be defined.The approach is made more complex by the non-linear behavior of the suspension and tires (Figure 7).If the load discharged on the rear wheels becomes too little, the vehicle’s performance will be affected. When braking, the load transfer is closely related to the longitudinal deceleration, the vehicle’s speed, and the transverse acceleration (braking in a curve). Thus it is demonstrated, based on the distribution of these forces, that there can be potential risks of instability from certain vehicle speeds based on the deceleration (Figure 8).This problem must be taken into account during the preliminary design phase for lightweight vehicles by modifying the position of the center of gravity, paying close attention to the front/rear weight distribution, or modifying the aerodynamic coefficient to hold the vehicle to the ground.Material worldMagneti Marelli has been working  on prototype composite suspension  components for some years now, writes  Graham Heeps. Having realized a mass- production-feasible, crash-safe, reinforced composite suspension arm that reduces component weight from around 1.5kg  for an ultralight steel version to no more than 0.85kg, the firm’s next target is to investigate the use of basalt- or glass-fiber to bring the cost down. The carbon-fiber version comes in at around five times the cost of the steel alternative.“In the next few years composite  materials will play a very important  role in automotive structural and safety components,” says Piero Monchiero,  suspension R&D manager at Magneti  Marelli. “We are starting to understand which are the right technologies and which will be the right technical solutions to  develop our parts and components with this kind of material.“We started with carbon fiber but along the way we’ve come to understand that it’s probably not necessary. Basalt and glass-fiber will probably be good enough for  conventional vehicles. The cost of glass and basalt is very acceptable but it is necessary to develop the technology a little bit to  verify their reliability over the long term. Our parts have a long life, 15-20 years, so we have to verify their safety. But I think that we are near to having good, light  materials [for suspension parts] using composites.”Magneti Marelli is studying the potential for composite knuckles and is also working on a front subframe made from a composite material. The latter probably won’t need reinforcement from a ductile material,  according to Monchiero.“For components like the arms,  which you have to sacrifice under crash conditions, yes it’s necessary,” he says. “But according to our first level of verification for subframes, it’s probably not. These  components have to be stiffer, more  resistant, so it probably isn’t necessary to use a hybrid [material] solution.”The rapid pace of development in  this area provides a real opportunity for innovation, Monchiero believes. “The base plastics materials are being developed very quickly. I see that when I talk to suppliers of plastic materials over the course of a few months, they tell me that they now have new materials available. For example, when we started work on the composite arm, we used a thermoplastic material because at the time, this was the plastic material with  the fastest curing time. But now thermoset materials are also achieving very short cure times, meaning that each operation needs less than one minute rather than the 10  or 15 minutes of before. We had to change to using thermoset material because the technology had developed so much.”The energy dissipated over braking time T is given by the equation:For example, a 1,400kg vehicle moving at 120km/h has to dissipate 776kJ of energy, which gives an average power of 141kW for a braking time of 5.5 seconds (deceleration of 0.6g). This energy that has to be dissipated has an impact on the force that has to be created inside the brakes. Decreasing the vehicle’s weight directly decreases the energy that has to be dissipated proportionately and therefore  makes it possible to use smaller brakes. The relationship between  the energy dissipated and the  size of brakes (and therefore  their weight) is not linear or continuous. For example, changing from 283 x 26 front disc brakes with caliper 60 to 266 x 22 front discs with caliper 57, related to a 150kg reduction in gross vehicle weight, saves 5.7kg for vehicles in the C segment.Weight reduction measures such  as this can create problems, however, as the example of high-speed braking shows. A vehicle at a standstill has an initial load distribution on the various wheels. When rolling, and especially in braking situations, the load on each tire will vary. This results in an additive or subtractive force based on the stress placed on the vehicle. A number of parameters influence this weight transfer including the vehicle’s weight,  the position of the center of  gravity, the wheelbase, the width  of the road, the downforces, and the tires’ performance. A D M AE x p e r t i s e i nG P S a n d I n e r t i a lM e t r o l o g yInertial / GPS System forVehicle Dynamics TestingGPS synchronizedeasy to usefast set-uplow data latency· Vehicle Dynamics Testing· Functional Safety Testing· Adjustment of Chassis Systems· Comfort Analysis· Tyre Testing· Deceleration / Acceleration Testing· Road Survey and Monitoring· Highly Precise Positioning· Verification of Simulation Models· Steering Robot Guidance· Driver Assistance Systems TestingGeneSys Elektronik GmbHwww.genesys-adma.de77656 Offenburg · GermanyTel.  +49 781 / 969279-0Tel. USA  +1 401-284-3750adma@genesys-offenburg.deGeneSysElektronik GmbHFIGURE 6: SLIP ANGLE AND RESPONSE TO A LATERAL FORCEFIGURE 7: TIRE’S DRIFT  RIGIDITY BASED ON THE APPLIED LOADFIGURE 8: DIAGRAM OF  STABILITY DURING THE BRAKING PHASE678

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Lightweight design: mass in transit

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