Romax electrical machine

NVH analysis

A workshop

Dr. Melanie Michon

September 2016

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© Copyright 2016

Agenda

• System approach to NVH analysis in electrified drivelines

• Overview of new electrical machine NVH software capabilities

o Electrical machine structural modeller

o Electrical machine dynamic analysis

• Demo of new electrical machine NVH software capabilities

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SYSTEM APPROACH TO NVH

ANALYSIS

For electrified drivelines

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Background

• Electrical machines are a critical part of many rotating machines

• Electrical machines are the future (and present) of automotive technology

• Electrical machines also appearing in many other applications, e.g.

o Wind turbines

o Marine

o Rail

o Aerospace

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NVH simulation of the complete electro-mechanical driveline to identify

system interactions from the start

Motor in isolation is okGearbox in isolation is ok

Put them together: there is a problem!!

PE E-motor

Gearbox

Experience shows that is it critical to

consider the electric machine and

gearbox together as part of the same

system

In this way electro-mechanical

interactions can be captured from the

start – target Right First Time design

This is particularly true for NVH

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Simulating NVH in an E-Powertrain

Radiated Noise = Excitation x Dynamic Response

MotorsEM Simulation -> Torque ripple

and radial forces

Simulation -> Reduction

System Response: Design

recommendations

Romax method for electromechanical system: True design for low noise

Conventional method: Design for low noise is “Design for Minimum Excitation”

System Response:

Simulation -> Reduction

Romax method for gears: Reduce system response

GearsLTCA -> TE

Simulation -> Reduction

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Motor noise mechanisms

• 1) Torque ripple

o Equal and opposite torque on rotor and stator

• 2) Radial forces

o Act between rotor and stator

o Forces on rotor cancel out

o Forces on stator generate complex force

shapes

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eNVH analysis – motor simulation

EM simulation of motor

in 3rd party FEA package

Obtain excitation

for stator forces …

.. and for torque ripple

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Frequency domain analysis of excitation data

8th harmonic 16th harmonic 24th harmonic

Harmonic

analysis

Complex stator radial force shape

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System response including mechanical and electrical

components

• Motor and gearbox in a single system

model

o Transfer path of torque ripple through

gearbox

• All shafts, bearings, gears, housing in

a single model

• Frequency domain solution for speed

and insight

PE

E-motor

Gearbox

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Unique analysis of electro-mechanical system interactions

H=48, 8472 rpmH=48, 936 rpm

1st stage, 8208rpm2nd stage, 6516rpm

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0 Mode

1

2

18

10

17

3

0.0E+00

5.0E-03

1.0E-02

1.5E-02

2.0E-02

2.5E-02

0 4000 8000 12000 16000 20000 24000

Velo

cit

y (

m/s

)

Input Shaft (RPM)

Structure-0Lobe_36Cycle Old_Structure-0Lobe_36Cycle

0 2400 4800 7200 9600 12000 14400

Radial Force- 0 Mode_36cycle Frequency (Hz)

0 25 50 75 100 125 150Vehicle Speed (km/h)

Reduction Factor = 0.22=13.22dB

Detailed design based on guidance from NVH simulation:

Noise Simulation becomes Noise Reduction

• Radial force excitation on electrical machine

• NVH analysis during concept design was used

to guide the detailed design

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NVH Simulation within the Design Process

• Predict noise at a time where it can be minimised

System Concept

Component

Detailing

Component Test

System Detailing/

Sub-system design

System test

Sub-system Detailing/

Component Selection

Sub-system test

No housing, but complete with

driveshaft and vehicle definition

Sum total power through bearings

Basic housing design

Mount stiffnesses from

reference data

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• Simulation of complete E-Powertrain

• Excitation from motor and gearbox sources

Simulation used in the design process to AVOID problems and

not just SOLVE them when they have occurred

Summary on eNVH analysis

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ELECTRICAL MACHINE NVH

New software capabilities

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What do the new modules do

• You can

o Create an electric machine assembly

o Create a concept stator component

o Import motor excitation data from 3rd party tools

o Define imbalance excitations

o Calculate whole system response to those excitations alongside usual

gear excitations

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Two New Modules

Electrical Machine Structural Modeller Electrical Machine Dynamic Analysis

Allows you to:

• Add “Electrical Machine” assemblies in the

model

• Create “Concept Stator” components and link

them to Electrical Machine assemblies

• Mesh a stator structure and conformally mesh

it to an FE shaft representing a stator housing

• Apply static forces and torques to stator and

rotor

Allows you to:

• Pre-process externally defined excitation data

• Define electrical machine dynamic excitations

• Have excitations that vary with speed

• View and export vibration response to these

excitations

Pre-reqs: Structural Flex, FE Solve Pre-reqs: Electrical Machine Structural

Modeller, System Dynamic Analysis

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Workflow

• Create Romax model of rotating parts and housing

• Create electrical machine assembly

• Mount rotor and stator to shaft and single axis housing as appropriate

• [Define and mesh concept stator] optional

• Define stator node connections

• Calculate electric machine excitations in 3rd party software

• Import excitation data

• Define any imbalances

• Run analysis

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STRUCTURAL MODELLER

For Electrical Machines

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Electric machine definition

• Comprises rotor and stator definition

• Both must be mounted before they can be edited

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Creating the rotor assembly

• The rotor is mounted on the input shaft

• The rotor is represented by its mass and

inertia

• Acts as Power Load for static analysis,

and excitation node for Dynamic Analysis

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Dynamic unbalance

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Creating and meshing a concept stator

• If the structure of the stator is not already

included in the housing mesh, a parametric

concept stator can be defined

• This can be meshed inside RxD and automatically

connected to the housing by a conformal mesh

• The housing should have a cylindrical bore where

the stator will fit

• The mesh from the inside of the housing bore is mapped on to the outer diameter of

the concept stator so that the meshes can be joined

• The benefit of this is that different machines can easily be analysed in the same

housing (although the housing must be re-condensed)

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Concept stator wizard

• Define stator

parameters:

o Diameters

o Slot/tooth

dimensions

o Number of slots

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Concept stator wizard

• Find housing nodes

at stator outer

diameter

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Concept stator wizard

• Mesh stator with

conformal nodes on

outer diameter

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Concept stator wizard

• Stator conformally meshed

with housing into single FE

component

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Connecting stator to FE housing

• Stator tooth connections

defined in node connection

dialog

• These RBE3 connections are

where the reaction torque

and motor excitations are

applied

• This step needs to be done

even if a concept stator is

not used

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Static Force analysis

• Static forces from the electrical machine, i.e. DC torque and radial force,

can be defined manually, or populated from excitation data

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DEMO

Electrical Machine Structural Modeller

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NVH ANALYSIS

For Electrical Machines

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Importing excitations

• Motor excitations are calculated by 3rd party tools

• Torque ripple and radial force excitations are

imported into RomaxDesigner

• These are pre-processed into individual harmonics so

that the NVH behaviour can be analysed

• Excitations are calculated at different torque levels, for discrete speeds – typically 2-3

torque levels in drive and in coast

• The harmonics are interpolated across the speed range to give sufficient speed

resolution for the analysis

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Electromagnetic FEA software packages

• Motor excitation data is calculated by 3rd party tools

• Any electromagnetic FEA software can be used to calculate the excitation data

• For example:

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Example: Workflow of calculating the excitations in

Ansys Maxwell

• Draw e-machine in Ansys Maxwell

• Add appropriate boundary

conditions, magnet orientations,

phase windings and turns

• Define rotor band for torque

calculation

• Define tooth sections as separate

entities to calculate excitations

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Select each tooth and assign force individually

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Define current excitation

• Define phase current excitation

for given torque/ speed

condition

• Analyse transient model

𝐼𝑎 𝑡 = 𝐼𝑝𝑒𝑎𝑘 sin ω. t + θ

𝐼𝑏 𝑡 = 𝐼𝑝𝑒𝑎𝑘 sin ω. t + θ −2π

3

𝐼𝑐 𝑡 = 𝐼𝑝𝑒𝑎𝑘 sin ω. t + θ +2π

3

ω = 𝑟𝑝𝑚360

60𝑝𝑜𝑙𝑒 𝑝𝑎𝑖𝑟𝑠 ∗

𝜋

180

Θ= gamma angle for given torque/speed condition

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Plot motor torque and export to csv

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Plot forces on each tooth

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Export tooth forces to csv file

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Importing excitations

• Excitation data is imported through the pre-processor in the electrical

machine assembly

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Importing excitations

• In this example 4 speeds are defined

• The excitation data exported from external FEA can be copied directly from spreadsheet if excitation data is

provided for all teeth, for one rotation

o Where periodicity has been used to speed up the FEA analysis, it is up to the user to pre-process the data

to create a full data set

• This process will be more automated in future releases

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Importing excitations

• Imported excitations can be visualised

• Dominant harmonics are extracted

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Unbalance excitations

• A shaft that is not balanced exerts a rotating radial force on

the shaft proportional to the square of the rotation speed

• Electric machines can run at very high speeds and these

forces can be large and also be at frequencies which are

audible

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Speed-dependent general excitationsRequired for electrical machines

• The electric machine excitations have an amplitude which varies with frequency or

speed

• Users can now define general excitations that vary with speed

• Electric machine excitations are a special case of general excitation that are grouped

together for convenience

• Speed dependent general excitations are available in the Advanced Whine module.

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Speed-dependent general excitations

Required for electrical machines

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DEMO

Importing and Pre-processing the Excitations

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Calculating NVH performance

• Once the electric machine and

excitations are defined then the

vibration response can be calculated

using the advanced whine analysis

• Motor excitations are passed

automatically to the Dynamic

Analysis Results window and are

automatically applied to the rotor

and to each stator tooth

• Motor excitations and imbalance are

shown alongside gear transmission

error

Gear transmission error

Motor excitations

Imbalance

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Calculating the system response

• System response can be calculated in

different ways:

o Response at the mounts

• Assess structure-borne noise

o Response at virtual accelerometer

locations

• Correlate with test data

o Calculation of the Mean Square

Velocity of the housing

• Initial indication of air-borne

noise

o Export to acoustic analysis software

for more detailed analysis

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Response at housing mounts

Differential

mount

Motor mount

Gearbox mount

Select mount

locations

Select excitations

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ODS generation at key frequenciesFor the mount velocity response to 48th Harmonic Radial force & Torque ripple

• Identify most significant excitation

mechanisms and speeds

• Generate ODS (Operating Deflection

Shape) animations at each mechanism

and speed

• Identify locations with greatest response

Peak in response on

motor-end mount

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Define virtual accelerometer locations

• Response nodes are chosen to correspond to accelerometer locations

474710157

9008

19049

8788

1862463816851

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Response at virtual accelerometers

• Response to gear or motor

excitations at virtual

accelerometers

o Correlate to test data

o Identify locations with

highest response

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Dominant response identified in peaksVirtual accelerometer velocity – motor excitation

• Examination of individual virtual accelerometers

• Response to 48th excitation is dominated by motion

at B-end bearing cover

• ODS confirms significant response at this location

H=48, 10 440 rpm

4747

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Calculate Mean Square Velocity on the housing

• Calculate Mean Square

Velocity across all surface

nodes, or a selection of nodes

• Response to e-machine

excitations, imbalance and

gear TE

• Apply A-weighting to

represent non-linearity in

perceived loudness

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Calculate Mean Square Velocity on the housing

• Overlaying Mean Square

Velocity for each excitation

shows relative importance of

each excitation

• Most significant excitations

here are 1st and 2nd stage TE,

and motor 48th order

excitations

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Design recommendationsReducing the excitations: Machine design

• Motor excitations

o 48th harmonic of radial force and torque ripple is most

significant contributor to structure-born and air-born

response

o Electrical Machine pre-processor provides insight in where

to focus electrical machine design improvements to

reduce excitations:

• The amplitude of 48th harmonic of radial force is relatively low

compared to lower harmonics

• The amplitude of 48th harmonic of the torque ripple is high

compared to other harmonics

o Analysis module provides insight in how to reduce system

response to electrical machine AND gear excitations

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System response to e-machine AND gear excitationsAnalysis provides unique insight which allow for reducing system response

• Peaks are identified in system response to e-machine AND gear excitations

• ODS gives great insight in system deflections – allows for design recommendations

H=48, 8472 rpm

H=48, 936 rpm

H=48, 50 rpm

H=40, 10224 rpm

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• Peaks are identified in system response to e-machine AND gear excitations

• ODS gives great insight in system deflections – allows for design recommendations

1st stage, 8208rpm

Unbalance, 12000 rpm1st stage, 6516rpm

Unbalance, 864 rpm

System response to e-machine AND gear excitationsAnalysis provides unique insight which allow for reducing system response

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DEMO

Analysis results

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Benefits

• This unique capability allows engineers to analyse the NVH performance

of the complete electric machine and gearbox system quickly and easily

• Experience has shown that analysing electric machine and gearbox

separately can lead to incorrect design decisions

• This new capability allows problems to be identified and fixed early in

the development phase as part of a Right First Time development

process

• Expect to see much more electric machine capability in Romax software

over the coming months and years