ELECTRIC MOTORSSIMULATION APPLICATIONS STREAMLINE THE
DEVELOPMENT OF ELECTRIC VEHICLE MOTORS
Volkswagen Kassel accelerates the design process for electric motors by building and distributing simulation
applications that evaluate the strength of rotor laminations.
By THOMAS FORRISTER

AS MORE CONSUMERS EXPRESS concern
for the environment, electric vehicles
are on track to outpace conventional
internal combustion engine vehicles
as the transportation mode ofchoice. In response to this growing
demand, leading automakers aredoing their part to pave the way forEVs, revving up the developmentof electric and hybrid motors
alongside the manufacturers ofcombustion engines. One suchautomaker is Volkswagen, whose
Kassel plant in Germany specializes
in the development, planning, andproduction of electric drives. It has
a production output of 150 electricand 300 hybrid drives daily.
As essential components in electric
drives, rotors need to be tested fordurability, since they must endure avery large number of revolutions atvarying speed and torque during drive
operation. However, evaluating thestrength of rotor laminations is timeconsuming. VW Kassel is automating
this test process for rotors, as well
as reducing development costs andincreasing product quality, by building
simulation applications with theCOMSOL Multiphysics® software.

torque, power, and speed for the main
rear-wheel drive and for the optional
front-wheel drive that is used inall-wheel drive versions (Figure 1).
Among other requirements, such as
the ratios for the axles, drive units,weight, and wheelbases, the design
and placement of the high-voltage
drive battery plays a major role in
the overall MEB concept. While theMEB helps to optimize individualcomponents and the system as awhole, balancing these requirements
takes careful consideration on thepart of the designer, especially when
accounting for new technologies
like digitalization, autonomous
driving, and electric drives.
From the very beginning of theelectric drive development process,there has been close cooperation
between staff involved in design,simulation, and testing at VW Kassel.
First, the simulation experts review
the performance specifications foran electric drive and use simulation
to investigate how to best approachthe design. For example, modelingthe drive greatly reduces the numberof variants, and distributing asimulation application based on
this model enables the designers
to then benchmark different
variants and choose the best one.
This collaboration is vital andbeneficial to all, as simulation
cannot cover all of the real-world
issues. Hence, the test process
plays an important role in thedevelopment process. In addition, theexperimental test procedure helps
to improve the simulation models.
“In the development process ofelectrical machines, one has to fulfill»

BALANCING ELECTROMAGNETICAND MECHANICAL REQUIREMENTS
IN 2015, VOLKSWAGEN began developinga modular system to optimize EV
design and make the manufacturing
process more efficient, called theModular Electrification Toolkit(MEB). The MEB accounts for theFigure 1. Schematic of the MEB, with the optional all-wheel drive (left, front of the vehicle) and themain drive (right, rear of the vehicle).

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ELECTRIC MOTORS

Figure 3. An example of the simulation application’s user interface.

Figure 2. A typical rotor setup with the rotor
plates, shaft, and magnet.

many requirements,” explains Dr.
Steffen Rothe, simulation engineerof component development at VW
Kassel. “On one hand, the machine
has to match electrical requirements
for the torque and power. On theother hand, the rotor has to possess acertain durability, where the centrifugal
force is the major load for the rotor.”
Further, balancing dual
requirements can be challenging,as they are sometimes at odds. For
example, while it is better to use
thin, weblike structures for theelectromagnetic requirements,
thicker structures are preferable formechanical durability. It is importantthat these requirements are addressed
early on in the development process.
One way to do so efficiently is tosimulate all of the load cases covering
the requirements. “Simulation,”
Rothe says, “plays a major role inaccelerating the design process.”“Many industrial simulation
programs are designed as a black box,
whereas COMSOL Multiphysics®
is unique in its transparency. It

4COMSOL MULTIPHYSICS

enables users to view and modify theimplemented equations, or even add
your own,” says Rothe. Furthermore
the software is designed as amultiphysics tool from the beginningand enables users to simulate different
physical fields simultaneously. Hence,
the user can combine different physicalfields to do something completely new.
However, analyzing complex
physical problems such as these canbe challenging, even for a simulation
expert. The team needed a way tocommunicate with colleagues andenable nonexperts in mechanicalsimulations to test certain parameters.
The designers were able to meet theseneeds by using the Application Builder, abuilt-in tool in COMSOL Multiphysics®,
to create simulation applications
that predict the stresses in a rotor.

»»IMPROVING EV PRODUCTION
WITH SPECIALIZED APPLICATIONSTO DESIGN AN APPLICATION for colleagues
to evaluate the strength and durabilityof rotor laminations, simulation experts
Marie Hermanns and Steffen Rothe

considered which part of the model
could be automated, which model
parameters were variable, and which
results the application should show.
For a typical rotor setup (Figure 2),
the simulation experts concluded thatthey could automate the load testing
to include interference, temperature,and operating speed. These areparameters that colleagues in otherdepartments would benefit from being
able to change themselves. Generalvariable parameters include geometry,area, interference, contacts, numberof active magnets, and materials.
These considerations helped
Hermanns put together an intuitive
user interface for the application(Figure 3) that colleagues could use
to automate the calculations needed.
“The idea was to create anapplication for colleagues to enable
an easy and fast way to benchmark
different designs,” Hermanns says.
“Additionally, one can create a tool fora specific problem with an intuitive
user interface. In this case, the user
does not have to learn the details

Many industrial simulation programs are designed as a
black box, whereas COMSOL Multiphysics® is uniquein its transparency. It enables users to view and modify the
implemented equations, or even add your own.”—DR. STEFFEN ROTHE, VW KASSELDECEMBER 2019of how the simulation works.”»STANDARDIZING DEVELOPMENT
TO SERVE COMPANY AND
CUSTOMER NEEDSIN ADDITION TO AUTOMATING thedevelopment process among
departments at VW Kassel,
specialized simulation applications
help the engineers standardize theirbenchmarking process of rotor laminations.
The application shortens the time it takes
to perform common tasks such as applying
boundary conditions, materials, and loads,
and is standardized and combined into
a user interface. A further benefit is theautomatically generated report, which
includes a strength rating for laminated rotor
sheet sections and helps to standardize thereport summaries across teams (Figure 4).

Through the stressanalysis of rotor laminations
using simulation
applications, engineers at
VW Kassel are able to savetime and money during
the development processof electric drives. The
applications also contributeto increasing product quality
by helping simulation
experts and nonexperts
alike automate the lengthy
model construction process
and standardize models
and results, shortening
the distance it takes to getfrom model to concept
vehicle to commerciallyavailable EV.

Top: Marie Hermanns(simulation engineer). Bottom:
Steffen Rothe (simulationengineer).

Figure 4. Standardized stress results for the rotor.

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