Improving off-road p gvehicle handling using

an active anti-roll baran active anti roll bar

PH CronjéPH CronjéSupervisor: Prof PS Els

1

Table of contentsTable of contents

• Statistics

• Problem statementProblem statement

• Theory

• Proposed solutions

• Simulations

• Design, manufacturing and testing

• ResultsResults

• Conclusion

2

Rollover accident statisticsRollover accident statistics• Number of rollover fatalities per million registered

vehicles, averaged from 1985 to 1990 in the United States

3

Rollover accident statisticsRollover accident statistics• Passenger vehicles involved in fatal accidents,

by vehicle body type in the United States

4

Problem statementProblem statement

• SUVs are growing in popularity

• Poor handling due to off-road capabilities

• Problem statement: Can the handling of an off-road

hi l b i d ith t th ifi f id f t?vehicle be improved without the sacrifice of ride comfort?

5

Theory: Steady state corneringTheory: Steady state cornering

6

Theory: Vertical load distributionTheory: Vertical load distribution

7

Theory: Static stability factorTheory: Static stability factor

t2 CG

tSSFh

=

• Determines if the vehicle will slide before it will roll

• To improve the safety of the vehicle, the following relationship must hold:

tμ <2 CGh

μ

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Theory: ConclusionTheory: Conclusion

If h l l l i i d h i i i• If the lateral acceleration is used as the optimizing variable, the vehicle will roll

• Previous work showed that body roll angle is a desired variable to optimized when improving handling for a predefined road and manoeuvrepredefined road and manoeuvre

• To improve handling:p go Lower the CG pointo Increase suspension stiffness and/or dampingo Add additional system which increases the roll

stiffness

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Solutions proposed in literatureSolutions proposed in literature

• Passive suspension

• Semi-active suspension

• Active anti-roll bar

• Active suspension• Active suspension

• Tilting vehicles

Each of these solutions will now be discussed

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Passive suspensionPassive suspension

• No energy is put

into the system and

no adjustments are

made during

operation

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Semi-active suspensionSemi-active suspension

• Only a small amount of energy is putenergy is put into the system with whichwith which adjustments are made to the system according to external inputs

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Active anti roll barActive anti-roll bar

• Anti-roll bar actuated by an actuator which is activelyAnti roll bar actuated by an actuator which is actively

controlled according to external inputs

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Active suspensionActive suspension

• A great amount of energy is put into the system andA great amount of energy is put into the system and

controlled by external inputs

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Tilting vehiclesTilting vehicles

• Vehicle leans into the turnVehicle leans into the turn

• Works only on narrow vehicles

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Selected solutionSelected solution

Question 1 2 3 4 5 6Question 1 2 3 4 5 6

Solution Weighting 0.2 0.1 0.2 0.2 0.1 0.2 Total Position

1. Passive suspension 10 9 4 2 10 7 6.5 4

2. Semi‐active damping 10 9 5 4 8 8 7.1 3

3. Active anti‐roll bar 10 9 7.5 5 6 9 7.8 1

4 Active suspension 10 8 8 7 3 8 7 7 2

• The solutions was weighted according to the selection criteria

4. Active suspension 10 8 8 7 3 8 7.7 2

criteria

• Selected solution: Active anti-roll bar

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Active anti roll bar (AARB)Active anti-roll bar (AARB)

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SimulationsSimulations

• Full non linear vehicle model in ADAMS 2005• Full non-linear vehicle model in ADAMS 2005

• Simulation uses Simulink and Matlab

• Adjustments to obtain correlation:

– Spring and damper characteristics

– Tyre characteristics

CG height– CG height

– Chassis torsional stiffness

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Correlation of baseline modelCorrelation of baseline model

4

6

MeasuredSimulated

2

eg)

0

Bod

y ro

ll an

gle

(De

-4

-2

3 4 5 6 7 8 9 10 11-6

Time (s)

19

Model proposed solutionModel proposed solution

• Proposed solution was modelled in ADAMS

• Simulations was used to obtain specific design variables andSimulations was used to obtain specific design variables and

predict results

Proposed solution• Proposed solution

predicts 80%

improvement in

body roll angley g

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Simulate proposed solutionSimulate proposed solution

4

6Body roll angle: Base vehicle vs AARB vehicle on flat road

Base vehicleAARB vehicle

2

4

e (D

eg)

0

rage

bod

y ro

ll an

gle

-4

-2Ave

r

0 1 2 3 4 5 6 7 8 9 10-6

Time (s)

21

Design manufacturing and testingDesign, manufacturing and testing

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Vehicle implementationVehicle implementation

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TestsTests

• Tests was performed as Gerotek Test Facilities, West of Pretoria

• The tests consisted of:

o Steady state handling test: Constant radius test

o Dynamic handling test: DLC manoeuvre

o Ride comfort test: Drive over the Belgian paving at constant speed

Each of these test will now be discussed

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Constant radius testConstant radius test

• Accelerate slowly from standstill while following a y g

constant radius around a point until the vehicle is

bl tunable to

maintain a

constant radius

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Double lane change manoeuvreDouble-lane-change-manoeuvre

f f• Enter first lane at a predefined speed

• Swerve to offset lane

• Return to original lane

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Ride comfort testRide comfort test

D i th B l i i i t i ht li ith• Drive over the Belgian paving in a straight line with a

constant speed

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Results: Constant radius testResults: Constant radius test

6

7

4

5

e (D

eg)

2

3

rage

bod

y ro

ll an

gl

1

Ave

-1 0 1 2 3 4 5 6 7 8-1

0

Lateral acceleration (m/s2)

Soft suspension, ARB disconnectedSoft suspension, ARB connectedSoft suspension, AARB

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( )

Results: DLC manoeuvreResults: DLC manoeuvre

5

6

Without ARBWith ARBWith AARB

2

3

4)

0

1

Rol

l ang

le (D

eg)

-2

-1

5 6 7 8 9 10 11 12 13-4

-3

Time (s)

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Results: Ride comfort testResults: Ride comfort test

• Vertical acceleration weighted according to the BS 6841 :• Vertical acceleration weighted according to the BS 6841 :

1987 standard for vertical vibration on a seated person

• RMS was calculated from weighted vertical acceleration

T t S i ARB tti W i ht dTest run no.:

Suspension setting:

ARB setting: Weighted RMS:

1 Soft Disconnected 1 43 m/s21 Soft Disconnected 1.43 m/s

2 Soft Connected 1.41 m/s2

3 Soft Active 1.44 m/s2

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ConclusionConclusion

• The AARB system shows a 74% improvement in• The AARB system shows a 74% improvement in maximum body roll angle during a DLC manoeuvre with the soft suspension over the base line vehiclethe soft suspension over the base line vehicle

• The AARB system showed no detrimental effect on theThe AARB system showed no detrimental effect on the ride comfort of the vehicle

• AARB system can dramatically improve the handling of an off-road vehicle without the sacrifice of ride comfort.

• Thank you for your time and safe driving!

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Thank you for your time and safe driving!