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Warning and Control of Vehicle Rollover Prevention Automotive Research Center

arc

Bo-Chiuan Chen

Prof. Huei Peng

Vehicle Active Safety Systems

Warning and ControlWarning and Controlforfor

Vehicle Rollover PreventionVehicle Rollover Prevention

Dept. of Mechanical Engineering and Applied MechanicsUniversity of Michigan


arc Rollover Fatality RatesRollover Fatality Rates

All Vehicles

Utility VehicleUtility Vehicle

Small Pickup

Standard Pickup

Small Car

Minivan

Standard Van

Medium Car

Large Car

Source: 1991-94 Average/Annual deaths per million registered vehiclesprovided by

19

28

34

40

47

59

93

98

47


arc Traffic Safety Fact 1996Traffic Safety Fact 1996


arc New SUV Rollover StickersNew SUV Rollover Stickers

News Released on March 5, 1999.


arc

Heavy Truck

Sport Utility Vehicle

Rollover Warning ApplicationRollover Warning Application

Pickup Light Truck


arc

¥Acceleration or Roll Angle Threshold-Early warning safety monitor

(Rakheja and Pich� 1990)

- Lateral load transfer ratio

(Preston-Thomas and Woodrooffe 1990)

-Rollover advisory sign on highway exit ramps (Freedmanet al. 1992)

-Automatic Truck Rollover Warning System

(McGee et al. 1992)

-Rollover stability advisor system

(Winkler et al. 1998)

Literature Review (Literature Review (Rollover WarningRollover Warning))


arc Literature Review (Literature Review (Rollover WarningRollover Warning))

¥Energy threshold-Rollover Prevention Energy Reserve (RPER)

(Nalecz et al. 1987)

-RPER = the energy needed to bring the vehicle to its tip-over position - the rotational kinetic energy

-RPER is positive for non-rollover cases, and when itbecomes negative, a rollover will occur if no action isdone to take energy out of the roll mode.


arc Disadvantages of Existing AlgorithmsDisadvantages of Existing Algorithms

¥The ÒdistanceÓ away from these threshold levels isnot an intuitive measure.

¥Use the information to determine the rollover threatat current time.

¥A method which assess rollover threat into thefuture, could give us a better perspective.

New Proposal: Time-To-Rollover (TTR) metricNew Proposal: Time-To-Rollover (TTRTTR) metric


arc Time To Rollover (Time To Rollover (TTRTTR))

¥¥TTR:TTR: Index defined to assess rollover threat in thisresearch.

Steeringangle Vehicle

Model

VehicleModel

Roll angle

TTRTTRRoll angle exceeds

threshold?

Roll angle exceeds

threshold?

Yes

now

Future

No

Time < 1sec?Time < 1sec?Yes No

TTR=1sec


arc TTRTTR CalculationsCalculations

Initial Conditions at the Kth Sampling Time

Steering Angle,Lateral Accel.

Steering Angle,Lateral Accel.

Roll Angle of theSprung Mass

Roll Angle of theSprung Mass

Model Integrated for up to 1 SecondsModel Integrated for up to 1 Seconds

TTRTTR(real-time)Lateral

AccelerationRollMotion

Steeringangle

YawModel

YawModel Roll ModelRoll Model TTR

Calculation

TTRCalculation


arc Desired TTRDesired TTR

¥For rollover cases, a straight line with slope= -1 iscreated starting from the rollover point backwardsin time.

¥It gives a uniform ÒcountdownÓ toward rolloverthreats and thus serves well as the basis ofwarning/control.

TTR=0.5TTR=0.5TTR=0.5 The vehicle will rollover0.5 sec later.


arc

Train NNto approachthe Desired TTR

Neural Network (Neural Network (NNNN) Architecture) Architecture

Layer 1Layer 1

Layer 2Layer 2

NN TTRNN TTRNN TTR

TTR fromSimplified Model

TTRTTR fromSimplified Model

Roll AngleRoll Angle

Change of RollAngle

Change of RollAngle

inputs

0 2 4 6 8 10 12-0.5

0

0.5

1

1.5

2

2.5

3

3.5

time (seconds)

output

DesiredDesiredTTRTTR

+-

0 2 4 6 8 10 12-0.5

0

0.5

1

1.5

2

2.5

3

3.5

time (seconds)


arc ArcSimArcSim Simulation Results Simulation ResultsEntering a Ramp

0 0.5 1 1.5 2-0.5

0

0.5

1

1.5

2

2.5

3

3.5

TT

R (

sec)

time (sec)

+ TTRx NN TTR

0 2 4 6 8 10-0.5

0

0.5

1

1.5

2

2.5

3

3.5Ramp Steering

TT

R (

sec)

time (sec)

0 1 2 3 4 5-0.5

0

0.5

1

1.5

2

2.5

3

3.5Obstacle Avoidance

TT

R (

sec)

time (sec)0 0.5 1 1.5 2 2.5

-0.5

0

0.5

1

1.5

2

2.5

3

3.5Worst-Case Steering

TT

R (

sec)

time (sec)


arc SUV Simulation ResultsSUV Simulation Results

0 0.5 1 1.5 2 2.50

0.5

1

time (sec)

TT

R (

sec)

0 0.5 1 1.5 2 2.5 30

0.5

1

time (sec)

TT

R (

sec)

Model based TTR of Samurai

(50 mph 0.6g right turn maneuver)

Model based TTR of Cherokee

(50 mph 0.6g right turn maneuver)

0 0.5 1 1.5 2 2.5 30

0.2

0.4

0.6

0.8

1

time (sec)

TT

R (

sec) Model based TTR

NN TT

Model based and NN TTR ofCherokee (50 mph 0.6g right turnmaneuver)


arc Reducing Time Delay Helps!Reducing Time Delay Helps!

¥Human delays (mean for brake reaction time~0.75 sec) creates unwanted vehicle and trafficbehavior. It was found that 0.5 (1.0) second ofadvance warning could prevent 30-60% (60-90%) of the accidents.

Advanced Perception

Reduction %of the Collisions

Intersection AccidentsAccidents withOn-Coming TrafficRear-End Collision

Source: Von Glasner AVECÕ94 002 9437953


arc Cherokee Model in TruckSimCherokee Model in TruckSim

Mechanical Simulation Corporation


arc

0 5 10 15-4

-3

-2

-1

0

1

2

time (sec)

m/s

2

Lateral acceleration

0 5 10 15-2

-1.5

-1

-0.5

0

0.5

1

time (sec)

deg

Vehicle roll angle

Model VerificationModel Verification

25 mph right turn (0.6g)50 mph pulse steer right

Lateral Accel.

Roll Angle

10 test runs

Input run

TruckSim

RMS value:

0.0379 g

RMS value:

0.2130 deg

0 5 10 15-7

-6

-5

-4

-3

-2

-1

0

1

0 5 10 15-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

time (sec)

Vehicle roll angle

Lateral acceleration

time (sec)

m/s

deg


arc

¥4-wheel Steering-Multiple Steered Axles for Reducing the RolloverRisks of Heavy Articulated Trucks.(Furleigh, Vanderploeg, and Oh et al. 1988)

¥Active Suspension-An Investigation of Roll Control System Design forArticulated Heavy Vehicles.(Sampson and Cebon 1998)

¥Differential Braking-Roll-Over Prevention (ROP¨) System.(Palkovics, Semsey, and Gerum 1998)

-Anti-Rollover Braking (ARBTM). (Wielenga 1999)

Literature Review (Anti-Rollover Control)Literature Review (Anti-Rollover Control)


arc

LongitudinalTire Force

LateralTire Force

Longitudinal Slip

Reduction in thetire lateral forcecomponent

Vertical tire load

Tends to zero by roll-over

Rolling over without

Differential Braking

Inertial force

High C.G.

ABS operation region

Physics of Differential Braking Control (I)Physics of Differential Braking Control (I)


arc

a v u ry = + ×˙

Longitudinalvelocity, u

d = constant

Lateral velocity, vacceleration, ay

Yaw rate, r

Physics of Differential Braking Control (II)Physics of Differential Braking Control (II)

Lateral tire force

Longitudinaltire force

Resulting Yaw moment


arc

¥The effect of differential braking has been includedin TTR calculation.

¥Braking moment is applied on the outside frontwheel while the vehicle is turning.

TTR Anti-Rollover ControlTTR Anti-Rollover Control

TTRCalculationTTRCalculation

TTR

SignSign

Preview ActionPreview Action Steering Input(Disturbance)

TruckSim CherokeeTruckSim Cherokee

BrakingMoment

ControllerController

DesiredTTR Differential

BrakingDifferentialBraking+

-


arc Simulation ManeuversSimulation Maneuvers

¥Step steering

100 km/h. (62mph)

¥Fishhook steering

100 km/h. (62mph)

0 1 2 3 4 5 6 7 80

20

40

60

80

100

120

deg

sec

Steering input

0 1 2 3 4 5 6 7 8-120

-100

-80

-60

-40

-20

0

20

40

60de

g

sec

Steering input


arc Step Response - Tire ForceStep Response - Tire Force

0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton

Fz of the left front tire

0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton

Fz of the right front tire

0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton

Fz of the left rear tire

0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton

Fz of the right rear tire

No controlP-control


arc Step Response - Roll AngleStep Response - Roll Angle

0 2 4 6 80

0.2

0.4

0.6

0.8

1se

cTTR

0 2 4 6 8-2

0

2

4

6

deg

Roll

0 2 4 6 80

500

1000

1500

N-m

Braking Moment

0 2 4 6 8-10

0

10

20

30

deg/

sec

Yaw rate

0 2 4 6 840

60

80

100

sec

km/h

Longitudinal speed

0 2 4 6 80

0.2

0.4

0.6

0.8

1

sec

gLateral acceleration

No controlP-control

Right

Start att=0.081sec


arc Fishhook Response - Tire ForceFishhook Response - Tire Force

0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton


0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton


0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton


0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton


No controlP-control


arc Time Delay of Control ActionTime Delay of Control Action

¥The control is turned on based on the threshold oflateral acceleration or roll angle.- Lateral acceleration threshold = 0.4g.Tdelay=0.091 sec.

-Roll angle threshold = 3 deg.Tdelay=0.257 sec.


arc Step Response - Tire Force. TStep Response - Tire Force. Tdd=0.257 sec=0.257 sec

0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton


0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton


0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton


0 2 4 6 80

2000

4000

6000

8000

10000

sec

New

ton


No controlP-control


arc ConclusionConclusion

¥TTR can provide preview rollover threat index.

¥Verified by using field test data (Cherokee).

¥TTR anti-rollover control can turn on the controlaction up to 250msec earlier than threshold (lateralacceleration or roll angle) based algorithms.


arc Future WorksFuture Works

¥Sophisticated controller design for TTR anti-rollover control.

¥Interactions between TTR warning/TTR anti-rollover control and drivers.

¥Human-in-the-loop driving simulator with TTRwarning/TTR anti-rollover control. (With OaklandUniversity.)

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