Multi Body Modeling for Ride Comfort Harshness approach

Copyright LMS International 1

Multi Body Modeling for Ride ComfortHarshness approach & methodologies

Andrew McQueen

Technical Manager – LMS UK

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Driving dynamics

The right tools for the right purpose!

Model complexity

Mo

delin

g a

ccu

racy

3D MBS 3D MBS/FEA

1D functional models 3D MBS rigid bodies flexible bodies non-linear

Real-Time enabling

Imagine.Lab Virtual.Lab SAMCEF Mecano


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Agenda

2 The harshness mechanism

1 Introduction

4

Simplified modeling for Harshness

5

Detailed modeling for Harshness

Conclusions

3

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Vibration Harshness

1 2 4 7 10 20 40 70 100

Hz

Powertrain

Engine

Steering

Brake

Tires

Suspension

Chassis Comfort

PitchRoll

Jerking

Drivability

Idle

vibrations

Steering

shudder

Steer

ability

Brake

judder

Shimmy

Chassis shake

Scanning, Rolling

Parking

Harshness

Stopping

distance

Simple to complex modelsFew parameters to many parameters are required

Increased CPU time

ISO & NHTSA

maneuvers

On centre

feeling

Tip in

Back out

NVH

Road noise

NVH

Powertrain

noise

contr

ols

Driving Dynamics in need of a mechatronic Systems Approach

Multi-disciplinary, covering wide frequency range, interconnected

Handling

Ride-comfort (Primary & Secondary) Noise


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Virtual Development Process: Classifying Subjects

� Handling 0 – 2 Hz

� Reaction of the vehicle to steering inputs (lateral dynamics), braking (longitudinal dynamics), …

� Constant radius cornering, step steer and release, ISO lane change, constant radius cornering, sweep input, brake in turn, rollover, … all ISO & NHTSA manoeuvres!

� Primary Ride 1 – 5 Hz

� The car body moves rigidly on the main springs (bounce, roll, …)

� Secondary Ride 5 – 15 Hz

� Suspension (wheel hop, axle tramp, fore-aft, …) and powertrain (bounce, roll, …) modes amplify excitations from road, wheel unbalance, engine idling, …

� Road shake, steering shimmy, impact harshness,

� Drivability 5 – 15 Hz

� Suspension (hop, tramp, fore-aft, …) and powertrain (bounce, roll, …) and driveline (torsional) modes amplify excitations from throttle input

� Tip-in/out, key-on/off, gear shift, idle regulation/engine control

� Vibration Comfort 15 – 50 Hz

� Excitations from P/T are amplified by resonances of vehicle body or auxiliaries

� Steering shake, floor vibrations, durability …

� Acoustic Comfort 20 – 10k Hz

� Airborne and structure borne excitation from road, P/T or auxiliaries

� P/T boom, gear whine, rolling noise, wind noise, HVAC noise, …

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Impact Harshness analysis


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Agenda


1 Introduction

4


5


Conclusions

3

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Impact Harshness ModelingGeneral MB modeling for ride

� Ride MB modeling includes two different levels of complexity, depending on the project phase considered and on the output to be evaluated:

� Simplified models, that describe few physical d.o.f. of the vehicle

� Full vehicle models, based on the assembly of main vehicle subsystems (suspensions, steering line, engine suspension, …)

Simplified ride models

Full vehicle ride models

Chassis virtual development timeline

Definition of suspension specification based on ride comfort

targets

Ride optimization and specification for chassis components and its interfaces

pp

CDTire


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Impact Harshness ModelingSimplified harshness model

11 d.o.f. model• as 6 d.o.f model• body longitudinal translation• front/rear unsuspended mass longitudinal translation

PerformanceBody longitudinal vibrations on a passage over obstacle

Output• suspensions longitudinal stiffness• kinematic longitudinal displacement in vertical travel of the suspensions

11 d.o.f. model• as 6 d.o.f model• body longitudinal translation• front/rear unsuspended mass longitudinal translation

PerformanceBody longitudinal vibrations on a passage over obstacle

Output• suspensions longitudinal stiffness• kinematic longitudinal displacement in vertical travel of the suspensions

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Impact Harshness analysisTire model


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Agenda


1 Introduction

4


5


Conclusions

3

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Impact Harshness analysis Impact Harshness & After shake

� Maneuver description

� Symmetric passage over rectangular obstacles

� Front and rear wheels separately

� At different speeds (e.g. 10 ~ 80 km/h)

� MB model description

� Flexible full vehicle ride assembly

� CDT20/30 formulation

� Controlled performances

� Fr & Rr seat rail long. & vert. acc.

� Damping rate of transient

� Output

� Suspension longitudinal filtering

• Longitudinal stiffness, wheel center longitudinal

• Displacement vs. wheel travel, tire dynamic characteristics

� Suspension vertical filtering

• Shock absorber characteristic

� Steering wheel vibrations

• Steering line stiffness, car body stiffness at the connection points, steering line and body dynamic coupling


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RIGID

full vehicle ride assembly

Full vehicle ride models

FLEXIBLE

full vehicle ride assembly

Ride components:

CD-Tire

PWT mounts

Shock Abs

Hydromount

+Rigid full vehicle handlingassembly

Ride components:

CD-Tire

PWT mounts

Shock Abs

Hydromount

+Flexible full vehicle handling

assembly

(T/B+ subframes)

General MB modelling for ride

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Harshness Multi-Body model

A full vehicle multi-body model is used for the harshness simulations.

It includes the following subsystems:

� Front/Rear Suspensions, including bushing dynamic stifness and flex subframes

� Steering system

� Tires (suitable for ride-comfort analyses, such as CDT or FTire)

� Powertrain (rigid) and P/T mounts

� Full trimmed body


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Harshness detailed Modeling & AnalysisMMC application case

LMS JSAE Conference 2005 - 373Paola Diglio , LMS Engineering Services, Italy

Joris Van Herbrugghen, LMS Engineering Services, Belgium

Valerio Cibrario, LMS Engineering Services, Italy

Hiroshi Yamauchi, Mitsubishi Motor Corporation, Japan

Masayuki Taketani, Mitsubishi Motor Corporation, Japan

Accurate Harshness modeling and analysis using multi-body CAE models

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� The parts of the model can be modeled as “rigid” or flexible. Rigid parts are

modeled by means of their inertia properties and center of gravity location.

� Flexible parts are modeled by means of a Craig-Bampton modal reduction of

their finite element models.

The modal base takes into account all the normal modes within a frequency

range that is reasonable for the analyzed phenomena and all the “static”

modes at the interface d.o.f’ s with the other parts of the multi-body model.

A structural damping ratio is also assigned to the flexible bodies.

� Front and rear subframes and the car body have been alternatively

represented by means of rigid parts or flexible bodies.


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Harshness Multi-Body model Bushing dynamic stiffness tuning process

In order to implement in the model the information about the dynamic behavior of

the bushings, a tuning process has been developed for the calculation of the

bushing dynamic stiffness.

That tuning process can be understood as follow:

� 1st step of the process:

Define a set of bushings that mainly influences the harshness response

� 2nd step of the process:

Obtain a dynamic stiffness vs input deformation level curve

� 3rd step of the process:

Define the deformation level/dynamic stiffness of the bushing

Software Limitation at the time – now tools will allow a dynamic

stiffness (amp + phase) to be defined for a bush

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CD-Tire 20 model

rigid ring model with (global) viscous-elastic sidewall,

geometrically parameterized normal contact and PDE

based tangential contact. It is suitable for excitation by

road profiles with long wavelengths.

� CD-Tire 30-model

flexible belt, rod-type in-plane model with (local) viscous-

elastic sidewall and brush type contact. The model is

suitable for excitation by road surfaces with short

wavelengths and a constant height profile in lateral

direction.

� CD-tire 40 model

flexible belt, shell-type 3D model with (local) viscous-

elastic sidewall and brush type contact. It can accurately

represent excitation by road surfaces in case with short

wavelength longitudinal and lateral height profile (e.g.

Belgian blocks, angled cleats, …).

pp

Rim

p

Rim

p

The LMS Comfort Durability Tire has been used to model the tire in the harshness multi–body full vehicle model.

CD-Tire is a family of 3 models (CD-Tire 20, CD-Tire 30 & CD-Tire 40) based on a macroscopic physical description of tires, which is a compromise between scope of applicability and speed.


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� Model parameters such as the belt bending stiffness essentially have to be determined by testing the whole tire

in a number of standard tire tests.

� They include static measurements (vertical + lateral stiffness, contact geometry), stationary measurements (pure

longitudinal slip, pure lateral slip, rolling resistance) and transient measurements (modal analysis of the free tire,

45° and 90° cleat runs). In order to insure sufficient accuracy over a broad application range, these

measurements typically are subject to variations of inflation pressure, preload and velocity (where applicable).

� Figure below shows the accuracy of the parameter identification process performed on the tire used in this

project:

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4000

0.0 0.1 0.2 0.3 0.4

Time, sec-1000

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2000

0.0 0.1 0.2 0.3 0.4

Time, secTime (sec)Time (sec) Time (sec)Time (sec)

——FxFx_measur ed _measur ed ——FxFx_calculated_calculated ——FzFz_measured _measured ——FzFz_calcu lated_calcu lated

Fx Fx (N)(N) FzFz (N)(N)

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0.0 0.1 0.2 0.3 0.4

Time, sec-1000

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Time, secTime (sec)Time (sec) Time (sec)Time (sec)

——FxFx_measured _measured ——FxFx_calculated_calculated ——FzFz_measured _measured ——FzFz_calcu lated_calcu lated

Fx Fx (N)(N) FzFz (N)(N)

Measured and calculated longitudinal (left) and vertical (right)

spindle forces at 20 km/h and 60 km/h

20 k

m/h

60 k

m/h

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Harshness simulation

� The condition simulated by means of the time-domain multi-body analysis is the

passage over a cleat with dimension: height 10mm, width = 50 mm.

� The tires impact perpendicularly the cleat and left and right tires simultaneously get

over the cleat (symmetric obstacle passage).

� Two different types of CD-Tire models are used in the simulations, in order to save

CPU time : a CD-Tire 20 (rigid ring model) in the transient phase of analysis, up to the

obstacle, and a CD-Tire 30 (flexible ring model) in the obstacle passing phase; the

switch between the two types is automatic.

� The simulation has been carried out at several car speeds: from 20 to 70 km/h with

step of 10 km/h.

� Moreover, the passage over the obstacle has been allowed separately for the front

and rear tires in order to better distinguish the two effects of the suspensions.

� The monitored performances are the peak-peak amplitude of the vertical and

longitudinal accelerations at the driver’s seat evaluated from the time history of that

data at different car speeds.


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The effect of the body flexibility on the final performance depends on both the characteristics of the

suspensions and of the body and on their coupling and then it cannot be neglected a priori: pictures

above show, for instance, a stronger effect of the body flexibility on the driver’s seat rail longitudinal

acceleration for a front obstacle passage and on the driver’s seat rail vertical acceleration for a rear

obstacle passage.

Figures below show the results obtained considering the front/rear subframes and the car body

respectively all rigid and all flexible:

Front tires obstacle passage

Rear tires obstacle passage

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� Two additional outputs have been extracted from the simulation in order to haveadditional guidelines for the front and rear suspensions design:

1. Difference between the peak-peaklongitudinal and vertical acceleration, due tothe front and rear obstacle passages.

2. Damping of the vertical acceleration atwheel centers respectively for a front andrear tires obstacle passages.


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Following test data were available:

� Time histories of longitudinal and vertical acceleration at front left wheel centerduring the front tires obstacle passage at 20 and 40 km/h;

� Time histories of longitudinal and vertical acceleration at driver’s seat rail duringthe front tires obstacle passage at 20 and 40 km/h;

� Peak-peak values of longitudinal and vertical acceleration at driver’s seat rail fora front tires obstacle passage from 10 to 80 km/h.

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The comparison between calculated and measured front wheel center accelerations in front

obstacle passage shows a very good correlation, mainly in longitudinal direction. This

demonstrates the validity of the tire model, that dominates the wheel center response.


at 20 km/h


at 40 km/h

Front wheel center accelerations


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The comparison between the calculated and measured driver’s seat rail accelerations in the

front obstacle passage shows again a very good correlation, mainly in the longitudinal

direction.


at 20 km/h


at 40 km/h

Driver’ s seat rail accelerations

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Peak-peak amplitude of the longitudinal and vertical driver’s seat acceleration predicted from

the multi-body model is completely within the dispersion of the test data.

Driver’ s seat rail accelerationsFront tires obstacle passage

Longitudinal Vertical


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Agenda


1 Introduction

4


5


Conclusions

3

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Impact Harshness analysis MMC case

� Graphs below show some results of a CAE-Test correlation of harshness:

Vertical

Front input @ 20 km/h

Longitudinal



Vertical


Longitudinal

Left front wheel center acceleration time histories

A flexible full vehicle model, with CDT30 tire model, has been used to simulate the passage of the front wheel over a symmetric obstacle (height = 10mm, width = 50mm) at some speeds.

Peak-Peak of driver’s seat rail longitudinal acceleration


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Conclusion

� A full-vehicle multi-body model has been made up for the simulation of the vehicle obstacle passage.

� Due to:

� Good accuracy of all the model parameters

� Effectiveness of tire model

the model has demonstrated to be able to predict the final harshness performance (driver’s seat rail acceleration) with a very good accuracy.

� Because of the completeness of the model itself, it can be easily used for many other ride-comfort and handling simulations, as well.

� Therefore, it represents a powerful tool in a multi–attribute optimization process.

� In a reverse engineering process, early in the development phase, the model can be also used to set-up the dynamic stiffness of the main bushing.

Thank you ! (For)(No) Questions ?

Documents

Multi Body Modeling for Ride Comfort Harshness approach