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magazine Nr. 19, IV-2014
Introducing
INEXAS: p.32
Future efficiency trends: p.20 BMW close-up: p.17
Main topic:
Noise, Vibration and Friction
Sustainable solutions, inspired by ecology and economy
Virtual acoustic design of engines ■ NVH Optimisation
Friction reduction ■ New NVH tools and requirements
With contributions of:
Graz University of Technology
CONTENT
0.2
8 10 14 0.1
z [m]
0
−0.1
−0.2
0.1
0 0.1
0
Silent Interior Reducing Friction Electric Vehicle
−0.1
Acoustics
−0.1
y [m] x [m]
Today, automotive engineers are facing new Reducing mechanical losses yields a signi- Automotive industry is asking for new metho-
challenges, among others the conflict between ficant contribution to reducing the fuel con- dologies to characterize the acoustic emissi-
good NVH performance and lightweight tar- sumption. Therefore, VIRTUAL VEHICLE in- ons of electric motors. VIRTUAL VEHICLE
gets. vestigates all important sources of friction in develops an experimental methodology based
the drivetrain on the FRIDA friction test bench. on cylindrical Nearfield Acoustical Holography.
24 26 28
Uncertain Component Systems Real-Time Simulation The Test Benches
The NVH optimisation of structural assem- VIRTUAL VEHICLE has developed new me- VIRTUAL VEHICLE operates comprehen-
blies requires detailed knowledge of all system thods for reducing low-frequency drive train sive test facilities designed to investigate the
components, especially when strong dynamic vibrations taking a parallel hybrid design as an acoustic properties of vehicle components
interaction occurs. Frequently, however, the example. such as the engine and drivetrain.
details of some components are missing de-
pending on the product requirements.
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EU Projects INEXAS Reliable Chain Drive Dynamics
Three ongoing Marie Curie Action projects at At VIRTUAL VEHICLE a 1D simulation tool has Considering the interaction of chain drive and
VIRTUAL VEHICLE focus on training of PhD been developed that simulates the acoustic engine structure is essential for simulation mo-
students in relevant NVH topics of automotive transmission behavior of the intake and ex- dels in acoustic optimization.
vehicle development. haust gas system and thus shows the acoustic
properties at the early design stage.
2 magazine Nr. 19, IV-2014
Spotlight on
NVH & Friction
17
Research and development in the fields of noise, vibration, harshness and
friction are of crucial importance for automotive industry. In the last decade
NVH has become part of a multidisciplinary design optimisation process,
also boosting the collaboration between the different research areas of the
VIRTUAL VEHICLE.
NVH Requirements
In response to the progressively more strin- TU Graz and KTH, researchers at VIRTUAL
Dr. MIHIAR AYOUBI gent environmental regulations in automotive VEHICLE develop efficient and reliable simu-
is Vice President Noise, Vibrations and industry, OEMs and their suppliers and part- lation and validation methods and support the
Harshness of BMW Group and talks about ners have significantly increased their efforts applicability of NVH virtual prototyping.
NVH requirements in vehicle development. towards eco-friendly vehicle developement
during the last years. Nevertheless, these in- Just in time for our 8th ISNVH Congress, this
novations – regardless if under development edition presents several research highlights:
or already implemented in series-production With new prediction methods for the acoustics
20 vehicles – shall not deteriorate the vehicle
NVH quality. In order to maintain the compet-
titive edge, the noise emission and passenger
of fiber reinforced plastics and efficient trim
characterization, relevant contributions to re-
liable NVH material modeling are provided.
comfort levels must meet or even exceed the A sophisticated model for the chain drive dy-
customer expectations also for the next gene- namics allows enhanced system understan-
ration of eco-friendly vehicles. ding. Extensive experimental facilities - from
acoustic engine test rig to friction dynamo-
Traditional challenges meter - are enablers for solving R&D challen-
meet new challenges ges at VIRTUAL VEHICLE.
MAN & AVL
Creative solutions for the conflicting demands In this magazine we also feature EU projects
ANDREAS Sommermann, jürgen
of lightweight design and excellent NVH has in the Marie Curie Actions, where VIRTUAL
ritter (both MAN Truck & Bus) and Dr.
become of central importance, involving no- VEHICLE has been successful in providing
Christoph Priestner (AVL List GmbH)
vel research in areas such as aeroacoustics, training to PhD students that goes far beyond
talk about the development of commercial
composite materials and full vehicle modelling. university education. We asked top-class part-
vehicles and diesel engines.
In addition, interactive effects of hybrid and ners from industry on innovative NVH solutions
electric drives, sophisticated turbo-charging and on future trends in engine development.
concepts, downsizing strategies and friction
reduction must be accounted for. We hope you enjoy the various contributions
23 In April this year, the EU parliament voted in
favour of a Commission proposal to decre-
in this edition.
ase vehicle noise in road traffic until 2026. A
decrease of noise limit values for passenger
cars, vans, buses and coaches by 4 dB(A) and
for trucks by 3 dB(A) are supposed to reduce
vehicle noise nuisance by some 25%. This will
require intensive R&D efforts in fields such as
A Successful Partnership tire acoustics, acoustic insulation materials as
well as intake and exhaust acoustics.
Prof. Mats Åbom
Department of Vehicle and Aeronautical Engi- Step by step to a solution
neering, Marcus Wallenberg Laboratory at Dr. Jost Bernasch Dr. Anton Fuchs
KTH Stockholm In close cooperation with leading partners in
science and industry, e.g. BMW, AVL, MAN or
magazine Nr. 19, IV-2014 3
Introduction
Challenges in the field of
NVH & Friction
Increasing fuel costs and stringent regulations on CO2 and other emissions are driving new development trends for
internal combustion engines, hybrid and electric drives and new energy storage technologies. Future vehicle concepts
must meet the conflicting demands of lightweight design, efficient and low-emission propulsion technologies, driving
comfort, suitable vehicle acoustics and low development and production costs.
D ue to factors such as the enormous econo-
mic growth of the BRICS countries (Brazil,
Russia, India, China and South Africa), the glo-
haust emissions have consequently moved to
the top of the agenda. This poses enormous
and frequently conflicting challenges to the
•
•
•
NVH materials & technology
Vehicle noise reduction
Friction loss & vibration reduction
bal demand for energy, and primarily for fossil OEMs who must assure low emissions and fuel • Flow acoustics
fuels, is increasing dramatically. As a result, efficiency without jeopardizing safety, comfort, • NVH Testing & measurement
energy is becoming more and more expensive, fun-to-drive and durability at an affordable and
which also increases the costs of mobility for competitive price. In order to assist automoti- NVH materials & technology
both business and private transportation. On ve industry as good as possible in this difficult
top of this, environmental sustainability has task Area NVH & Friction at VIRTUAL VEHI- New materials with enhanced characteristics
become a priority and fuel efficiency and ex- CLE focuses on the following topics: are enabling a further improvement of the NVH
properties of modern vehicle concepts.
Research topics of Area NVH & Area NVH & Friction has for instance con-
Friction at VIRTUAL VEHICLE
ducted detailed experimental and numerical
■ NVH DRIVETRAIN & investigations with regard to the acoustic be-
FULL VEHICLE: Reliable & havior of cellular metal foams. The microsco-
accurate dynamic, high-freq. pic material behavior is modeled with the
multiscale method, in order to calculate the
and full vehicle models
complete component efficiently.
■ FRICTION LOSS & Currently, research and development is focu-
sing strongly on multi-material applications for
TRIBOLOGY:
lightweight bodies combining aluminum, ma-
Journal-bearings,
gnesium, high-strength steels, CFRP and or-
cylinder-kit, timing- ganic sheets. Such materials will help to meet
drive, valve-train future requirements for lower weight, more sa-
fety, increased strength and increased comfort
■ INTAKE/EXHAUST: in terms of acoustics and vibration.
System Acoustics:
Accurate, user-friendly, From an acoustic point of view, lightweight also
general & fast models means easily excitable and therefore noisy and
loud. However, the customer is not prepared to
sacrifice today’s driving comfort. In order to de-
■ TRIM: Optimisation
sign an improved lightweight vehicle body with
of trim to reduce
suitable vibration and acoustics properties, the
interior noise structural dynamics, vibrating behavior, sound
transmission behavior and radiating behavior
have to be examined in detail in order to meet
■ LIGHTWEIGHT: the client expectations with regard to comfort.
Multi-scale modeling New simulation procedures are necessary for
approach, weight the virtual design of lightweight bodies in terms
reduction of engineering strength, crashworthiness and
vibration behavior.
4 magazine Nr. 19, IV-2014
The modeling of multi-layered composite ma- reduce friction in the powertrain, simulation Test benches for the support
terials in the acoustic frequency range still po- methods are required that can enable system- of vehicle development
ses a real challenge. Numerical results shall optimization measures in the early develop-
not only guarantee sufficient accuracy but ment phase. To this end, efficient and reliable VIRTUAL VEHICLE operates numerous
modelling efforts and calculation times must calculation methods are being developed at acoustic test benches, which are described
be compatible with the industrial processes in VIRTUAL VEHICLE, in order to meet industry in more detail on page 28. The engine test
automotive industry. Research work also fo- demands. bench is located in a full anechoic chamber
cuses on the non-destructive crack detection, for measuring vibrations, noise emission and
crack localization and damage detection of The various validated methods for the calcu- exhaust emissions from combustion engines in
fiber reinforced plastics via acoustic measure- lation of friction in the piston assembly, in the operation. The powertrain test bench is loca-
ment engineering. crankshaft bearings, in the valve train, in the ti- ted in a semi-anechoic chamber, in which the
ming drive and the transmission are the result vibrations and noise emission of entire drive-
Downsizing – a major challenge of a large number of industry-related research lines can be measured. In the modal analysis
for flow acoustics projects and strategic projects that have been test bench, the natural frequencies and eigen-
carried out in the last years. The engine fricti- modes of complex structures (e.g. the vehicle
Downsizing means reducing mass and engine on test bench FRIDA (see page 10) developed body) can be measured to be used for model
displacement while maintaining performance at VIRTUAL VEHICLE has been the last step updating. At the friction test bench, the engi-
levels. This can be realized, for example, by in this process and positions VIRTUAL VEHI- ne friction can be determined, as well as the
a reduction of the number of cylinders and by CLE in the front line of the research done in contributions of individual components (piston,
forced induction. Reducing the number of cy- this field of tribology. Through measurement- bearing, etc.) to the overall friction. The Sound
linders and optimizing combustion processes calculation comparison, the test bench offers Brick is a reverberation chamber that is similar
in combination with forced induction change the possibility to validate newly developed to a vehicle, in which material properties (e.g.
the NVH behavior dramatically. New methods calculation methods, to study material combi- sound insulation properties and absorption co-
and technologies are necessary in order to nations and coatings and to understand full- efficients) can be measured.
improve downsizing concepts, in particular system interactions. The comprehensive un-
with regard to vibration comfort and acoustic derstanding of tribological mechanisms forms This edition of the VVM presents selected re-
behavior. the basis for further research activities geared search activities of Area NVH & Friction and
towards the reduction of friction in combustion shows how new methods of simulation and
One important aspect related to downsizing is engines. experimental investigation are being pursued
the acoustics of intake and exhaust systems. based on existing experience from automotive
One of the core competences of Area NVH & NVH simulation and and rail technologies. ■
Friction is the precise prediction of the orifice measurement of the powertrain
noise of turbo-charged engines, based on im-
proved simulation methods for the individual There is still a great potential to improve con-
components (e.g. turbocharger, muffler, after- ventional propulsion concepts in order to fulfill
treatment of exhaust gases). To this end, all the high demands regarding fuel consumption
of the relevant disciplines are available in the and emissions. Virtual development methods
form of networked experts. can contribute significantly to this improvement about the authors
by enabling the modeling of future product re-
Friction reduction in engines quirements in a faster, yet cheaper manner. To
and transmissions achieve this, however, the powertrain must be Dr. Anton Fuchs is
taken into consideration more strongly in the Head of Area NVH & Friction
Increasingly stringent exhaust regulations are early stages of development without losing at VIRTUAL VEHICLE.
forcing OEMs to continuously increase the effi- sight of the full-vehicle requirements. Cur-
ciency of their vehicles. In modern combustion rently, rapidly advancing developments in the
engines, approximately 70% of the fuel energy field of electrification of the powertrain pose
is lost through heat (60%) and friction (10%). new challenges due to increased complexity,
Only about 30% of the provided fuel energy is a greater amount of variants, and the demand EugEne Nijman is
available as usable power at the crankshaft. for more interdisciplinarity and improved con- Scientific Head of Area
Since the usable power is further reduced by sistency in the development process. To this NVH & Friction at VIRTUAL
the transmission, wheel bearing, tires, etc. in end, VIRTUAL VEHICLE supports OEMs and VEHICLE.
the end, only 20-25% of the provided fuel ener- suppliers with application and industry orien-
gy is used for propulsion. In order to effectively ted research in the field of NVH and friction.
magazine Nr. 19, IV-2014 5
Lightweight Acoustics
Reinforced Plastic Components
in Vibroacoustic Simulation
Plastic components are more and more used in modern vehicles. Besides conventional plastics, fiber reinforced
plastics show a high potential for lightweight construction and currently strongly expand into structural parts.
VIRTUAL VEHICLE investigated requirements for the acoustic simulation of structural parts in the powertrain made
of fiber reinforced plastics.
C arbon fiber reinforced plastics weigh
around 60% less than steel and about
30% less than aluminum. This high potential
Challenges for acoustic simulation
of fiber reinforced plastics
Commercial FE-software tools already include
elements for an orthotropic material definition,
but still combined with damping approaches
for lightweight design and hence for CO2 re- Fiber reinforced plastics show a strongly aniso- not being able to introduce a damping direc-
duction is the reason why automotive industry tropic behavior compared to metals. It is mainly tivity.
puts so much effort in a cost-effective produc- caused by the material properties, -compositi-
tion suitable for high quantities. on and the manufacturing process. In Fig. 1 a Finite Element and
cross section through a material probe is given, Multi Body Simulation
The acoustics of fiber reinforced plastics repla- manufactured by injection-molding. It shows a
cing metal powertrain parts is of high interest, typical composition in three layers consisting VIRTUAL VEHICLE investigates the require-
due to the fact that lightweight structures show of two boundary layers with a fiber direction ments for the Finite Element (FE) and Multi-
disadvantages in the acoustic mass damping parallel to the border as well as in flow direction Body (MB) simulation of fiber reinforced pla-
effect. In addition, the most effective way (con- of the melt and an intermediate layer with or- stics based on plate probes (short glass fiber
cerning costs and weight) to reduce unwanted thogonal fiber direction. Averaging the material reinforced polypropylene with 40% glassfiber
noise shares is directly at or near the source. properties over the whole thickness results in content). Therefore, in the simulation different
In case of the powertrain this means for ex- a higher E-modulus in the main fiber direction, homogenizations and damping approaches
ample to directly reduce the noise emission of this corresponds with the longitudinal mold flow available in FE and MB simulation code were
the engine by optimizing covers and general direction. In addition, also the material damping compared to measurements. For the homoge-
structures primarily before increasing the air shows a directional property. The highest dam- nization, the whole plate thickness and a layer-
borne sound transmission by adding additional ping occurs in a direction rotated about 45° to wise approach were compared. The FE-model
damping material to the firewall. the main stiffness direction. consists of shell elements, with an orthotropic
material definition based on engineering con-
stants. In the FE-simulation, the main vibroa-
coustic properties including eigenfrequencies,
eigenmodes and transfer functions were ana-
lyzed and compared to measurements. For the
time domain simulation in a MBS software tool
the FE-model of the specimen was reduced in
complexity. The mode shapes were taken as a
basis to take the anisotropic material behavior
into account.
In the MB simulation, the damping behavior is
introduced via Rayleigh approach.
Acoustic validation measurements
The validation measurements were carried out
with the specimen clamped on one end and ex-
Fig. 1: Reflected-light microscopy and cited with a volume velocity source or impulse
indicated fiber orientation across a cross hammer on the other end. The clamped speci-
section of the probe men was chosen to compare the measurement
6 magazine Nr. 19, IV-2014
Fig. 3: Comparison of
measured and simulated
transfer function
results with the time domain simulation results like a plate. In this frequency range some that the orthotropic material behavior has a
in the MB simulation environment. Generally, deviations between measurement and simu- significant impact on the structural dynamics
the MB simulation time domain solution (series lation can be observed. Different modeling and therefore has to be considered in the si-
of single sinusoidal force excitations) yields approaches based on a three layer approach mulation process.
very similar results as the FE-simulation in fre- for the plate thickness or different damping
quency domain. approaches (structural and modal damping) Expertise established in this field includes ho-
do not show a real improvement of the simu- mogenization procedures, model complexity
The comparison of the FE eigenfrequen- lation results in this frequency range. These reduction methods and approaches how to
cies shows good correspondence with the deviations can be traced back to changes in model the correct damping of fiber reinforced
measurements, deviations are less than 3% the fiber orientation over the length and width
for all modes. The modal assurance criterion of the test specimen, currently not included in
(MAC) calculates the correlation of different ei- the model. ABOUT THE AUTHORS
genvectors from simulation and measurement
results. The MAC values for the modes up to Summary
Dr. Josef Girstmair is
700 Hz are in a good consistency. Above 700
leader of the powertrain dy-
Hz, the MAC values are lower but the visible Researchers at VIRTUAL VEHICLE investi-
namics and acoustics group
comparison still shows a good congruence, gated the vibroacoustic behavior of fiber rein-
at VIRTUAL VEHICLE.
see Fig. 2. forced plastics experimentally and developed
an efficient method to simulate their behavior.
The comparison of transfer functions confirms This method has been successfully applied
the good consistency up to around 1000 Hz for simplified components. It can be seen as
(see Fig. 3). In this frequency range the speci- a relevant contribution to predict lightweight Elmar Böhler is Senior
men mainly behaves like a beam, indicated by acoustics in an early vehicle design phase. Researcher in the vehicle
a falling mean transfer function characteristic. noise reduction group at
Above 1000 Hz, the specimen behaves more Based on the investigations it could be shown VIRTUAL VEHICLE.
Thomas Schaffner is
Senior Researcher in the
powertrain dynamics and
acoustics group at VIRTUAL
VEHICLE.
Fig. 2: MAC and comparison of the sixth
torsional eigenvector of the probe.
magazine Nr. 19, IV-2014 7
Silent Interior
A Novel Approach for
Trim Characterisation
Automotive industry is more and more driven by the need to offer fuel-efficient and eco-friendly mobility. Today,
lightweight design, downsizing of internal combustion engines along with hybridisation of powertrain are the main
strategies pursued by the most OEMs in order to increase the vehicle performance and to reduce its fuel consumption
and exhaust gas emissions. At the same time, the lightweight design is expected to worsen the air borne insulation
performance of future vehicles. Automotive engineers are therefore facing new challenges, namely the conflict
between good NVH performance and lightweight targets.
A common strategy to reduce vehicle inte-
rior noise consists in the application of
sound insulation and absorption materials (see
Fig. 1). Lightweight structures, however, show
strong interaction with these sound insulation
and absorption treatments. In order to optimise
the acoustic design of the future road vehicles,
an efficient method for accurate description
of the structure-trim-cavity interaction in the
frequency range up to 2000 Hz is of high im-
portance. Fig. 2: The concept of Patch Transfer Function (PTF) method
The challenge In order to overcome these limitations, an al- tion Approach (PTF) [1] as an alternative me-
ternative trim characterisation procedure is thod to predict the vehicle interior noise. The
When tackling vibro-acoustic problems in- requested by the vehicle industry. PTF is a sub-structuring method, which consists
volving porous materials, a full finite element in partitioning of the problem into sub-systems
modelling scheme based on complex material The novel approach and coupling them at their common interfaces
micro-models is typically adopted. via impedance relations (see Figure 2).
Over the recent years, a consortium of BMW
Unfortunately, as far as industrial problems AG, IAC Group GmbH, Microflown Technolo- First, the full trimmed body (i.e. vehicle struc-
are considered, this state-of-the-art approach gies, ESI GmbH and Université de Sherbroo- ture plus trim) is divided into individual sub-
leads to very demanding calculations, which ke, Canada, under the lead of VIRTUAL VE- systems: vehicle structure, trim and the pas-
today limits its practical application for the low HICLE has developed a novel, experimental senger compartment air cavity. The interfaces
frequency range up to 300 Hz. Moreover, the- trim characterisation method to describe the between each sub-system are discretised into
se models typically require a whole set of ma- interaction between vehicle structure, trim and a low number of elementary surfaces, called
terial parameters describing the vibro-acoustic cavity (i.e. passenger compartment). patches, which have typically the size of 20
behaviour of a poro-elastic trim. In practice, by 20 cm. For each patch, the complex spa-
these parameters are acquired by highly speci- In this research project, VIRTUAL VEHICLE tial distribution of sound pressure and parti-
fic experimental techniques and are therefore proposed the so called Patch Transfer Func- cle velocity is averaged resulting in only one
very expensive or even not available. quantity - the patch impedance. To predict the
behaviour of the full system, the superpositi-
on principle is employed. As a result, the PTF
approach allows for independent sub-system
characterisation.
Where simulation fails,
test takes over
One of the main advantages of the approach
proposed is its high flexibility with respect to
Fig. 1: Common strategies for interior noise reduction (structure- and airborne sound)
8 magazine Nr. 19, IV-2014
Fig. 3: Validation test case Fig. 4: Comparison of the full-system measurement (red) and the PTF reconstruction (blue)
the acquisition of the impedances at the cou- at VIRTUAL VEHICLE. It allows for the vibro- References
[1] Ouisse M. et al., “Patch transfer functions as a tool to
pling interfaces. These impedances can be acoustic properties of layered trim media to couple linear acoustic problems”. Journal of Vibration
obtained in experimental, numerical and - if be measured directly without the need of ha- and Acoustics, DOI:10.1115/1.2013302.
applicable - even analytical manner. ving complex material parameters available. [2] Rejlek J. et al., “A combined Computational-Experimental
Approach for Modelling of Coupled Vibro-Acoustic
The material data acquired by the test rig is Problems”, DOI:10.4271/2013-01-1997.
This seamless combination of the experimen- compatible with the PTF description and can
tal approach (e.g. for structure or trim) and the be further used in the coupling process in a
numerical approach (e.g. for the cavity) de- straightforward way.
monstrates the full versatility of this coupling ABOUT THE AUTHORS
procedure. It allows sub-systems exhibiting The proposed PTF approach has been vali-
low modal density to be modelled by conven- dated by an appropriate test case. A clamped
tional finite element method (FEM), whereas steel plate has been damped by a layer of Dr. Jan Rejlek is Team
sub-systems, which are already too complex porous material and coupled with a rigid rec- Leader of Vehicle Noise
for an FE description to be characterised in ex- tangular cavity. The test case is represented Reduction group at VIRTUAL
perimental manner. As a result, the strengths in Fig. 3. VEHICLE.
of both approaches can be fully exploited in
one combined procedure. The individual sub-systems have been cha-
racterised separately in experimental, nume-
A fully flexible workflow rical and analytical manner. The PTF method Giorgio Veronesi is
has been applied to predict the behaviour of Marie Curie Researcher
Both numerical and experimental sub-system the full-system. Results obtained inside the involved in the EU Project
characterisation techniques of the enhanced acoustic cavity by means of the PTF method “GRESIMO“ at VIRTUAL
PTF have been developed and implemented at are compared with the results of a direct VEHICLE.
VIRTUAL VEHICLE [2]. For a numerical deter- measurement conducted on the assembled
mination of interface impedances, a commer- system (see Fig. 4). The PTF method, which
cial FE package has been employed. merely utilises information of the separate
sub-systems such as structure, trim and cavi- Eugene Nijman is
The experimental characterisation relies on ty, shows high reliability and good predictabili- Scientific Head of Area
the application of an array of pressure and ty of the full-system behaviour. NVH & Friction at VIRTUAL
velocity sensors for non-contact surface VEHICLE.
measurements. Since both the sound pressure Conclusions and outlook
and the particle velocity are measured simul-
taneously, the interface patch impedances can The long-term goal is to adopt the enhanced
be determined in a very efficient way. PTF technique as a new, future approach for
evaluation and target setting of automotive Dr. Arnaud
Experimental trim characterisation sound packages. In this respect one can fully Bocquillet is project
and validation exploit the main advantages of this technique, engineer at BMW AG.
being an independent characterisation of the
In the proposed PTF methodology, the trim individual sub-systems and the full flexibility
material is characterised experimentally. To with respect to choice of the characterisation
determine the trim patch impedances, a de- scheme. ■
dicated test rig has been designed and built
magazine Nr. 19, IV-2014 9
Testing and Simulation
Reducing friction
to make drivetrains more efficient
Reducing mechanical losses (friction) yields a significant contribution to reducing the fuel consumption. Therefore,
VIRTUAL VEHICLE investigates all important sources of friction in the engine and the transmission both on the
FRIDA friction test bench and by means of accurate simulation, in order to develop ideas for their reduction.
A long with lightweight construction and the
shift of the thermodynamic load point in
the engine (downsizing), friction reduction is a
very powerful tool which enables the most im-
portant sources of friction in the engine and
transmission to be accurately identified. As a
bilities for measuring the mechanical efficiency
of engines and even complete drivetrains (e.g.
for motorcycles under high loads).
very effective way of reducing fuel consump- result, targeted optimizations can be prepared
tion. On the race track, a friction-optimized with this information. Accurate and reproducible measurements also
drive train achieves a greater distance bet- enable the exact determination of the advan-
ween pit stops for refueling and thus saves Friction measurements tages achieved by reducing friction when new
valuable time. coatings or low friction oils are used, which
At VIRTUAL VEHICLE, there are several test can consequently provide the technical basis
VIRTUAL VEHICLE investigates the drive benches available to measure the friction in for manufacturing decisions. The results can
train, which is a combination of engine and the engine under realistic loadings. In parti- likewise be used to carry out benchmarks with
transmission, as a complete system. The com- cular, the friction test bench FRIDA (friction existing solutions.
bination of simulation and measurement is a dynamometer, Fig. 1) offers very flexible possi-
Fig. 1: FRIDA friction test bench (friction dynamometer)
at VIRTUAL VEHICLE
10 magazine Nr. 19, IV-2014Fig. 2: FMEP measured by means of FRIDA
for the drive train of a super sport motor cycle
Classification of losses cation data is available at VIRTUAL VEHICLE, A simulation method has been developed at
by simulation which enables a meaningful evaluation of the VIRTUAL VEHICLE that enables an assess-
lubrication. ment of the losses on the individual compo-
While measurements are very useful, they nents to be carried out in conjunction with
cannot determine the causes or the main sour- Since the transmission is an important part of current efficiency measurements on transmis-
ces of friction in the engine or transmission. the drive train, it is also the object of friction in- sions.
vestigations. In general, manual transmissions
For this purpose, very powerful and accurate are considered to be very efficient. However, In order to identify the important sources of
simulation models have been developed at since this efficiency is only achieved at high friction in a transmission, a simulated friction
VIRTUAL VEHICLE, which enable a thorough loads, at low loads there is always a significant loss distribution was carried out. Fig. 5 shows
investigation of the sources of friction in all re- potential for friction reduction. the results that were achieved for a manual
levant parts of the drivetrain.
Therefore, it is possible - for example after
a frictional power measurement on the test
bench - to accurately determine the losses
in the individual groups, such as the pistons,
journal bearings and valve train of a car en-
gine. In this way, the total losses, as well as
the valve train and gas exchange losses, are Fig. 3: Calibration of strain
measured, and the losses in the journal bea- gauges for the measurement
of valve train losses
rings are accurately determined by simulation.
The simulation method necessary for this was
comprehensively validated and scientifically
published in [1 and 2], among other places.
Using this combination of measurement and
simulation, the distribution of the losses can
be determined for a particular car engine for
almost any operating point (speed and load).
Fig. 4 shows a relevant example for a 4-cylin-
der car engine.
With these simulation models, it is also possi-
ble to investigate the lubrication conditions in
these groups and the feasibility or the friction
advantage that could be obtained by the use
of low friction oils, for example. The necessa-
ry expertise in the field of modern low friction
lubricants was obtained during the work on se-
veral projects. The relevant rheological lubri-
magazine Nr. 19, IV-2014 11Fig. 4: Typical distribution of the losses for a car engine, carried out at VIRTUAL Fig. 5: Determination of the losses in the individual com-
VEHICLE. A more detailed numerical assignment of the amounts shown for the ponents of a manual transmission by simulation compared
individual piston rings, etc. is also possible. with the measurement of the total losses on the test bench
transmission. As an example, the transmis- ponent increase significantly as a result. Since have less friction than journal bearings. Con-
sions investigated showed quite high conical piston pin failure leads to serious engine da- sequently, efforts have been made to replace
roller bearing losses, which could be reduced mage, a very detailed and extensive simulation the crank assembly bearings, which make up
by the use of alternative bearings. method was worked out at VIRTUAL VEHICLE a significant part of the total losses, with roller
to investigate this critical component. bearings.
Detailed tribological investigations
A model was developed considering the ther- However, it is important to consider not only
Even if friction occurs generally in all parts of mo-elastic deformations of piston and pin, as the higher manufacturing costs resulting from
the drive train, with some components, energy well as the free-floating bearing, which was the use of roller bearings in this application,
losses are less important than reliability in ser- able to describe the slow rotary movement but also their unfavorable NVH (noise, vi-
vice, for example. of the pin as well as its change of direction at bration and harshness) properties. With the
certain operating points. The results were in competence available at VIRTUAL VEHICLE
One example of such a component is the pi- good agreement with the measured data. Fig. regarding journal and roller bearings, it is also
ston pin; its free-floating bearing causes hardly 6 shows an example of the pressure distributi- possible to make a comprehensive compari-
any frictional losses. Due to the increasing loa- on calculated with this model. This information son of both solutions for the assessment of the
dings caused by increasing power densities, can now be used for targeted optimizations of friction and NVH properties.
it has to operate under increasingly extreme existing solutions.
conditions (rising temperatures, lack of lubri- Conclusion
cation, etc.). In certain cases, available lower friction al-
ternatives have other design disadvantages. Friction is a phenomenon that occurs every-
The problems with this apparently simple com- It has long been known that roller bearings where. It is necessary to find a special solution
for each specific problem, which typically me-
ans typically that a suitable compromise with
other requirements must be found.
At VIRTUAL VEHICLE, friction is considered
as a property of the complete system. There-
fore, models are available for all important as-
semblies, which also enable detailed investiga-
tions of other properties (NVH behavior, etc.).
In particular, in terms of friction reduction, it is
no longer possible to make significant savings
by redesigning only a single individual compo-
nent. Significant savings can only be obtained
in conjunction with other measures, such as
optimized thermo-management, reduction of
the pumping power, ancillary units or the chan-
ge to a low friction lubricant or use of coatings.
Fig. 6: Calculated pressure distribution At VIRTUAL VEHICLE, the ability to consi-
on a free-floating piston pin der the complete system as a combination of
12 magazine Nr. 19, IV-2014measurements and detailed simulation enables
realistic investigations of the potential for friction
reduction, and the identified friction advantages
can then be achieved in practice. ■
References:
[1] H. Allmaier, C. Priestner, C. Six, H.H. Priebsch, C. Forstner, F.
Novotny-Farkas, Tribology International 44 (2011), S. 1151ff
[2] H. Allmaier, C. Priestner, D.E. Sander and F.M. Reich (2013).
Friction in Automotive Engines, Tribology in Engineering, Dr.
Hasim Pihtili (Ed.), ISBN: 978-953-51-1126-9, InTech, DOI:
10.5772/51568. Free download available at:
http://tinyurl.com/mp9tng6
Test rig to determine
engine friction losses
■ Reliable measurements for gasoline
and Diesel engines
ABOUT THE AUTHORS ■ For series engines and prototypes
Dr. Hannes Allmaier
■ Concurrent determination of losses
is Lead Researcher for in sub-systems
Friction and Tribology at
VIRTUAL VEHICLE. ■ Partial- and full load engine tests
■ High flexibility for various applications
Franz M. Reich The Friction Dynamometer FRIDA has been developed at VIRTUAL VEHICLE.
Group Leader This test bench can measure not only the magnitude of the total friction losses
Tribology and Efficiency in the engine, but can also determine the specific contributions of the individual
Area NVH & Friction components (i.e. the piston assembly, crank drive friction bearings and valve
train). In contrast to conventional strip-down methods, these measurements
are carried out concurrently for all subsystems under the same realistic opera-
ting conditions.
The newly established test bench is well-suited for a variety of applications -
Co-authors from friction loss determination in driving cycles to the assessment of coatings,
low-viscosity engine oils or other constructive measures.
T. Schaffner
D. Sander
Contact and Information:
C. Knauder
DI Mag. Franz Reich Dr. Hannes Allmaier
Tel.: +43-316-873-4001 Tel.: +43-316-873-4006
Area
NVH
X - Cross
& Friction
Domain
E-Mail: franz.reich@v2c2.at
magazine E-Mail: hannes.allmaier@v2c2.at
Nr. 19, IV-2014 13Electric Vehicle Acoustics
An Experimental Method for the
NVH Characterization of
Electric Motors
Automotive industry is asking for new methodologies to characterize the acoustic emissions of electric motors,
since their integration in EVs and Plug-in-Hybrid vehicles is growing. At VIRTUAL VEHICLE we are developing an
experimental methodology based on cylindrical Nearfield Acoustical Holography. This allows the evaluation of sound
intensity, as well as pressure level and particle velocity. It is suitable for any type of electric motor without knowing
either the internal geometry or the material properties.
Need for new NVH methodologies State-of-the-art for electric motor full knowledge of the material properties is
suitable for electric vehicles NVH simulation needed. In practice, this turns out to be ex-
tremely difficult for coils and lamination pack
Automotive industry is increasingly driven by There are three main approaches to predict or structures that are typical for some motor ty-
the need to offer fuel-efficient and eco-friendly characterize the vibro-acoustic behavior of an pes.
mobility. This is mainly achievable by light- electric motor, i.e. analytical, numerical and
weight design, downsizing internal combustion experimental. Measurements are then the most reliable way
engines, and powertrain electrification and to characterize the motor as an airborne sound
hybridization. Moreover, customers are asking Analytical approaches are usually fast and source. At Area NVH & Friction we are deve-
for comfortable and innovative vehicles. simple to apply, but their high accuracy is limi- loping an experimental method to characterize
ted to very simple geometries. the airborne noise emission of electric motors,
In order to accomplish customer expectations, which are typically almost cylinder-shaped.
new NVH approaches are required. They have Numerical methods (finite and boundary ele- This characterization method is based on
to deal with new materials, components and ments) can include fine geometry details, but acoustical holography in cylindrical coordi-
powering strategies. In this framework, the have as drawback a less flexible workflow nates, i.e. implying the measurement of the
prediction and characterization of the noise of and long computational time, especially if sound field in discrete positions on a cylindri-
electric motors plays a crucial role. high frequencies are included. Moreover, the cal surface around the electric motor [1].
Proposed methodology
Cylindrical Nearfield Acoustical Holography
(NAH) allows an accurate localization and
0.2 characterization of a source through the back-
propagation of a hologram, being thus extre-
mely well suited for cylindrical sources like
0.1
electric motors.
Cylindrical NAH consists in the following four
z [m]
0
steps:
−0.1
1. measurement of the pressure on a grid
of points on the hologram surface (i.e.
−0.2 microphone positions)
2. computation of its spectrum through a
0.1 spatial transform
0 0.1 3. propagation of the spectrum and re-
0 construction of the velocity distribution on
−0.1 −0.1 the source surface
y [m] x [m] 4. back-transformation to the real space
Fig. 1: Electric motor surface (green points) and microphone positions (blue stars)
14 magazine Nr. 19, IV-2014130
125
120
115
110
VL [dB]
105
100
95
90
85 Fig. 2: Comparison of source velocity level (VL)
along the circumference: Real velocity (dashed
green), NAH not regularized (dashed blue) and
80
0 pi/2 pi 3pi/2 2pi NAH regularized (solid blue)
θ [rad]
We created a numerical test case to investi- NAH is based on an inverse problem, which Practical aspects of cylindrical
gate practical aspects of cylindrical holography is sensitive to small input variations (e.g. holography
such as hologram size and possible sources of measurement noise). The robustness of the
error. Such simulations allow for designing an method is enhanced by filtering the noise com- Several scenarios have been examined in
effective experimental setup. ponents (i.e. regularization). order to investigate practical aspects of cy-
lindrical holography such as microphone po-
Fig. 1 shows the geometry of the test case; Fig. 2 shows this regularization effect at a sin- sitioning error, background noise, hologram
the green points represent an acoustic sour- gle frequency step along the circumference of distance, spatial sampling, measurement
ce (motor) while the blue stars are the micro- the motor and emphasizes the importance of aperture. Fig. 3 and 4 show the spatially ave-
phone positions. this step for NAH. raged square error (ε) for different hologram
8
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The multi-functional, wireless SIZE
O
measurement system with MICR
integrated sensors for multi-
purpose measurement tasks: minimal
●● Forces and inertial measurement unit design size
●● Temperature, air pressure, humidity
●● Position determination (via GPS)
E OUS
TI-US
●● Flexibly upgradeable: 23 input/output
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channels for external sensors, 5 bus
systems for direct communication
MUL AUTO
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On-board sensors Intelligent energy management
Wireless communication Integrated power supply
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Request your test kit now !
Contact and
Information:
DI Michael Lieschnegg VIRTUAL VEHICLE - Kompetenzzentrum Tel.: +43-316-873-9001
Tel.: +43-316-873-9030 Das virtuelle Fahrzeug Forschungs-GmbH Fax: +43-316-873-9002
E-Mail: michael.lieschnegg@v2c2.at Inffeldgasse 21a, 8010 Graz, AUSTRIA E-Mail: office@v2c2.at
magazine Nr. 19, IV-2014 156 4
2 mm
3 4 mm
4
6 mm
3 dB error band 8 mm
2
2 3 dB error band
1
0
ε [dB]
ε [dB]
0
−2
−1
lho = l
−4
lho = 1.5*l −2
lho = 2*l
−6 lho = 3*l −3
lho = 4*l
−8 −4
0 500 1000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 3000 3500
freq [Hz] freq [Hz]
Fig. 3: Spatially averaged square error Fig. 4: Spatially averaged square error (ε) with microphone positioning error. The
(ε) for five different hologram lengths legend refers to the standard deviation of the positioning error (σ xyz).
lengths and microphone positioning errors, pical magnitude of this noise does not compro- References
[1] M. Kirchner, E. Nijman, “Nearfield Acoustical Holography for the
respectively. It can be observed in Fig. 3 that mise the results. characterization of cylindrical sources: practical aspects”, in pro-
for a microphone array of 1.5 times the motor ceedings of 8th International Styrian Noise, Vibration & Harshness
Congress (ISNVH 2014), Graz, Austria
length, the maximum error is within the 3 dB Cylindrical holography allows for accurate
range. Furthermore, the same error band in- acoustic characterization also in the presence
cludes the effects of a microphone positioning of sources located on the end caps of the elec-
error of up to 8 mm (Fig. 4). tric motor, such as a cooling fan and bearings.
Conclusions and future work The frequency range is limited by the number
ABOUT THE AUTHORS
of microphones used. Future work will further
Matteo Kirchner
Cylindrical NAH is an efficient method for the investigate the topic in order to understand
is Marie Curie Researcher
characterization of the acoustical emissions how many microphones can be excluded
involved in the EU Project
of electric traction motors for next generation without compromising the results.
„eLiQUiD“ at VIRTUAL
green vehicle applications.
VEHICLE.
Free-field measurements on a real electric mo-
Numerical simulations at VIRTUAL VEHICLE tor will be performed in an anechoic chamber
have already shown that cylindrical NAH - toge- in order to verify and validate the proposed
ther with an appropriate regularization scheme methodology. ■
- gives accurate results for the reconstruction EugEne Nijman
of the surface velocity of an acoustic source is Scientific Head of Area
like an electric motor. NVH & Friction at VIRTUAL
VEHICLE.
Measurement noise can be limited by
choosing anechoic test environments. The ty-
24th International Symposium
on Dynamics of Vehicles
on Roads and Tracks
August 17-21, 2015
Graz / Austria
Research Center
www.IAVSD2015.org
16 magazine Nr. 19, IV-2014Interview:
Dr. Mihiar Ayoubi, BMW GROUP Germany
NVH Requirements
in Vehicle Development
New materials such as carbon fiber reinforced plastics and aluminum, electrification and
hybridization concepts create a huge challenge for powertrain-, tire- and wind NVH. Understanding
all the relevant NVH causal loops is the key to create innovative solutions. Dr. Mihiar Ayoubi, Vice
President Noise, Vibrations and Harshness of BMW Group shared his thoughts with us.
VVM: What are the main current trends in au- VVM: Where do you see the most important and high-frequency areas can be significantly
tomotive R&D concerning NVH? technical challenges of NVH-related vehicle extended. This primarily affects phenomena
development? for tire and wind NVH.
AYOUBI: The first essential trend is the in-
creased expectations of the customers with AYOUBI: The largest challenge for the NVH The goal has to be to analyze, design and va-
regard to NVH comforts. In this respect, not development in the vehicle is the expansion lidate as much of the NVH world in the vehicle
only the noise level is crucial, but also the NVH of the physical understanding of the relevant as possible via virtual prototyping because vir-
coherence between wind-/ tire-/ powertrain- NVH causal loops. For me, a causal loop is tual prototyping has become an essential de-
NVH in the vehicle is becoming increasingly only fully developed when it is also depicted velopmental tool in the development process.
important. in the virtual world. Only then it becomes pos-
sible to develop the NVH property through VVM: In which phases of the BMW vehicle de-
The second defining trend is of course light- objective goals in a directed manner, from the velopment process is NVH integration current-
weight construction and emission reduction design to the integration and validation. ly of particular importance?
with direct interaction with NVH. The employ-
ment of new materials such as carbon fiber Some NVH phenomena were understood very AYOUBI: Generally speaking, in the past NVH
reinforced plastics and aluminum, the trend well and also depicted operatively in the virtual development focused more on the integration
towards downsizing and down-speeding, the world. This is the case with powertrain NVH. phase. In this phase, the analysis, problem-
electrification and hybridization entail many However, I have also observed that the depic- solving, and optimization were always handled
challenges for NVH engineers. tion of other NVH phenomena in the medium using HW-prototypes. 8
With the i8, BMW has introduced a technology carrier with many innovations
that all were a huge challenge for powertrain-, tire- and wind NVH.
Source: BMW
magazine Nr. 19, IV-2014 17Since then, we have made a significant leap In the second derivate development phase, AYOUBI: Simulation, driving test, and test
towards a more balanced NVH development the NVH character should be applied based on bench trials are development tools that focus
throughout the product development process. a well-designed platform for each vehicle deri- on different applications. The product develop-
To this end, basic NVH elements are designed vate, in order to guarantee a segment-specific ment process passes through different pha-
iteratively at a very early stage via simulati- positioning. ses, in which specific questions are prioritized.
on and simulators (global and dynamic stiff- To this end, the phase-adequate deployment
nesses, aerodynamic shapes, integration of Virtual prototyping has of one or more tools is necessary. In the early
transmission and chassis,…). become an essential phase, in which there is no hardware, simula-
developmental tool in tion plays a central role. In the later phase, in
VVM: And how do you think this will change in the development process. which the refinement takes place, the experi-
the future? mental trial is the faster way.
VVM: How do you see the development of EU
AYOUBI: The trend towards an early NVH legislation concerning noise emission, and VVM: What is the BMW strategy for handling
integration via virtual prototyping and NVH what are the consequences for BMW? the trade-off between lightweight design and
simulators will be expanded. The product de- acoustic comfort?
velopment process is essentially based on two AYOUBI: The advanced draft proposals for
phases: an architecture phase and a derivate exterior noise call for new boundary values AYOUBI: Many small steps will be required to
development phase. and new test cycles. resolve the conflict in objectives between light-
weight approaches and NVH and to produce
The goal of the architecture phase is to design With the previous test specifications, the an optimum solution.
the NVH genes for a broad platform in a target- powertrain was the dominant source of exte-
oriented fashion. I am talking about the NVH rior noise. With the new test cycle, the tire will To this end, one essential step is a sound NVH
backbone of a platform. Clearly, errors in this now become the dominant emitting source. backbone in the form of static and dynamic
respect have significant consequences on la- Consequently, the automotive and tire indus- stiffness. It is also becoming increasingly im-
ter derivatives. The second challenge of this try has to develop new technologies in order to portant to prevent noise emission at its source,
phase lies in the lack of hardware prototypes. meet the challenging tire goals such as rolling before the energy goes downstream into the
This is where NVH simulation in the sense of friction, driving dynamic, breaking distance, or body. In the body, new lightweight materials
NVH virtual prototyping plays a key role. This NVH. with good dampening characteristics are ne-
is the reason why I see the expansion of the cessary.
understanding of the physical NVH causal VVM: Will it be possible to replace experi-
loop as the primary challenge for NVH deve- mental NVH investigations in the vehicle de- VVM: Where do you see potential for improve-
lopment. Only this can enable a reliable NVH velopment process completely with simulation ment in conventional drivetrain NVH?
virtual prototyping. within the next ten years?
The emotionalizing effect of sound only transpires
through the context and interplay of all senses -
haptic, optic and acoustic- in the vehicle.
Source: BMW
18 magazine Nr. 19, IV-2014AYOUBI: High supercharging, downsizing, the vehicle. The emotionalizing effect of sound by the hand does not exhibit the desired proac-
downspeeding are dominant trends in the only transpires through the context and inter- tive behavior.
powertrain development with NVH conflict. In play of all senses - haptic, optic and acoustic-
this context, it is imperative to ensure further in the vehicle. VVM: What is your experience in cooperating
NVH isolation close to the source and within with VIRTUAL VEHICLE?
the internal engine. VVM: What are the demands for NVH engi-
neers at BMW? What attributes and values AYOUBI: VIRTUAL VEHICLE has an impres-
VVM: Which R&D achievements in your area should they represent? sive network of competent and highly motiva-
of responsibility are you most proud of? ted experts who pursue an interdisciplinary
AYOUBI: We place value on an exceptional approach. I like that. ■
AYOUBI: I think right away about the i8. With education, a marked proactive behavior, the
the i8, we have introduced a technology carrier ability to take a systemic perspective, and a
with many innovations, including the carbon- tangible passion for the product and the topic.
Dr. Mihiar Ayoubi has been interviewed
fiber body, a highly supercharged 3-cylinder
by Dr. Anton Fuchs.
across the back axle, a directly connected High supercharging, down-
chassis and a life-drive module, to name but a sizing, down-speeding are
few. All these topics were a huge challenge for dominant trends in the
powertrain-, tire- and wind NVH. powertrain development
with NVH conflict.
We are quite proud of the result. Driving the i8
brings an intense emotional driving pleasure. VVM: What are your expectations in a re-
search partner?
VVM: What is characteristic and relevant for a
high-quality brand sound at BMW? AYOUBI: A cooperation partner should have
a sound theoretical competence and at the
AYOUBI: Sound design at BMW is authentic. same time a strong emphasis on practical ap-
Sound design is not a question of the power- plications and an economical implementation.
train alone. The perception of the engine A project should not take too long to deliver re-
torque disappears after seconds of accelera- sults. In executing projects, our partner should
ting. It is much more important that we fulfil have a similar work culture to that of BMW.
customer expectations regarding exterior and Passion, perfection and the never-ending love
interior design and the feeling of space within for the product. A partner that needs to be led
Dr. MIHIAR AYOUBI
is Vice President Noise, Vibrations and
Harshness of BMW Group.
Graduate degree and doctorate in Control
Systems Engineering from the Technical
University of Darmstadt. Joined BMW in
1997. Held various positions in the series
development of mechatronic systems, such
as electronic steering systems, breaking
control systems, all-wheel-drive systems,
manual transmission, powertrain and vehicle
assistance systems. Since 2011, VP of
acoustics and vibrations in the full vehicle.
Dr. Ayoubi is one of the distinguished
Keynote Speakers at the ISNVH 2014
Congress in Graz: „Challenges of virtual
prototyping for premium NVH comfort -
an overview of current BMW engineering
practices“.
More information: www.isnvh.com
magazine Nr. 19, IV-2014 19You can also read
