Light Vehicle Dynamic Rollover Propensity Phases IV, V, and VI
Transcript of Light Vehicle Dynamic Rollover Propensity Phases IV, V, and VI
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Light Vehicle Dynamic Rollover Propensity Phases IV, V, and VI
Research Activities
Garrick J. Forkenbrock
W. Riley GarrottNHTSA Vehicle Research & Test Center
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Overview of NHTSA Rollover Research Phase I-A
• Spring 1997 • Exploratory in nature • Emphasized maneuver
selection and procedure development
Phase I-B • Fall 1997 • Evaluation of test driver
variability • Introduction of the
programmable steering machine
Phase II • Spring 1998 • Evaluation of 12 vehicles
using maneuvers researched in Phase I
PhasesPhase IV
• Spring 2001 • Response to TREAD
Act • Consideration of many
maneuvers Phase V
• Spring 2002 • Research factors that
may affect dynamic rollover propensity tests
• Rollover and handling rating development
Phase VI • Evaluation of 26
vehicles using Phase IV recommendations
Phase III-A
• Spring 2000
• Introduction of “Roll Rate Feedback”
Phase III-B
• Summer 2000
• Pulse brake automation
Discussed in this presentation
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Phase IV Background
TREAD Act / Congressional Requirements: • Develop dynamic rollover propensity tests to
facilitate a consumer information program • Consumer Information methodology released by
November 2002 • National Academy of Sciences Report
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Additional Background
In their assessment of NHTSA’s existing rollover resistance rating system (January, 2002) the National Academy of Sciences recently recommended:
“NHTSA should vigorously pursue the development of dynamic testing to supplement the information provided by SSF.”
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Additional Background
• NHTSA is presently providing Rollover Resistance Rating
• Based on vehicle measurements and real world crash data
• Vehicle measurement is Static Stability Factor
• 5 Star ratings are similar to NCAP Crash Ratings
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T/2
Hcg
Weight W
Pull Impending Rollover W(T/2)=P(Hcg) Pull/W = (T/2)/ Hcg Pull/W=SSF
Weight WNo Force
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50%P
roba
bilit
y of
Rol
love
r per
Sin
gle
Veh
icle
Cra
sh
40%
30%
20%
10%
0%
1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.55 1.6
Static Stability Factor
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Maneuver Recommendations
•Alliance of Automobile Manufacturers •Consumers Union •Ford Motor Company
•Heitz Automotive, Inc.
•ISO 3888 Part 2 Consortium
� VW, BMW, Daimler Chrysler � Porsche, Mitsubishi
•MTS Systems Corporation
•Nissan Motors •Toyota Motor Company •UMTRI
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Phase IV Test Conditions
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Test Vehicles
2001 Chevrolet Blazer 4x2 � One star static rollover rating � High sales volume
1999 Mercedes ML320 4x4� “Less aggressive” stability
control intervention � Two star static rollover rating � First SUV with available stability
control (ESP)
2001 Ford Escape 4x4 � Three star static rollover
rating � Smaller, car-like SUV
2001 Toyota 4Runner 4x4� “Aggressive” stability control
intervention � Two star static rollover rating � Relatively high sales volume
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Vehicle Configurations
•Instrumented
•Fully fueled
•Front and rear mounted aluminum outriggers
•Performed with and without stability control
•Multiple configurations � Nominal vehicle� Reduced rollover resistance
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Reduced Rollover Resistance
•Roof-mounted ballast •Designed to reduce SSF by 0.05 •Increased roll inertia from Nominal condition � Escape = 8.0 % � Blazer = 11.5%
•Longitudinal C.G. preserved Up to 180 lbs •Maneuver sensitivity check
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Reduced Rollover Resistance(measurements taken without instrumentation)
4Runner � 180 lbs ballast � C.G. raised 1.3” � SSFNOMINAL = 1.11 (��) � SSFRRR = 1.06 (��)
Blazer � 180 lbs ballast � C.G. raised 1.3” � SSFNOMINAL = 1.04 (��) � SSFRRR = 0.99 (�)
Escape � 120 lbs ballast � C.G. raised 1.0” � SSFNOMINAL = 1.26 (�� ��) � SSFRRR = 1.21 (���)
ML320 � 180 lbs ballast � C.G. raised 1.2” � SSFNOMINAL = 1.14 (���) � SSFRRR = 1.09 (��)
Note: Nominal SSF differ from those measured without outriggers13
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Test Vehicle SSF Summary
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0.90
1.00
1.10
1.20
1.30
Blazer 4Runner ML320 Escape
Stat
ic S
tabi
lity
Fact
or (S
SF)
Baseline
Nominal (no instrumentation)
Nominal (with instrumentation)
RRR (no instrumentation)
SSFnom,i = 1.05
SSFnom,i = 1.12
SSFnom,i = 1.18
SSFnom,i = 1.27
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Tires
•OEM specification (as installed on vehicle when delivered) � Make � Model � DOT Code � Inflation pressure
•Frequent tire changes •Innertubes used during some maneuvers to prevent debeading •Maneuver speed iterations selected to minimize tire wear within a given test series
Test surface damage due to debeading
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Test Surface
• All tests performed on TRC’s VDA (a dry, high-mu asphalt surface)
• Tests performed 04/01 to 11/01, 02/02 • Stable friction coefficients� Peak mu: 0.94 to 0.98
� Slide mu: 0.81 to 0.88
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Phase IV Maneuver Review
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Characterization Maneuvers
• Used to define NHTSA’s dynamic rollover propensity maneuvers � Constant Speed, Slowly Increasing Steer
• Used to characterize transient response � Pulse Steer � Sinusoidal Sweep � J-Turn Response Time Tests
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Dynamic Rollover Propensity Maneuvers
Automated Steering� NHTSA J-Turn � Fixed Timing Fishhook � Roll Rate Feedback
Fishhook � Nissan Fishhook � Open-Loop Pseudo-
Double Lane Change
Driver-based Steering � ISO 3888 Part 2 � CU Short Course
Driver-based Steering, Computer Corrected � Ford PCL LC
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NHTSA J-Turn and Fishhooks
• Steering magnitude based on vehicle response 300
250
1. Determine the handwheel 200
angle at 0.3 g from Slowly 150
100Increasing Steer results 50
2. Multiply by a scalar (derived 0
0 500 1000 1500 2000 2500 Count Number
with Phase II data) 0.7• Steering rate based on 0.6
0.5successful Phase II testing 0.4
0.3
� J-Turn = 1000 deg/sec 0.2
0.1
0
� Fishhook = 720 deg/sec -0.1
R2 = 0.99281
ac tua l linear fit
0 500 1000 1500 2000 2500 Count Number
Lat
eral
Acc
eler
atio
n (g
) H
andw
heel
Ang
le (
degr
ees)
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NHTSA J-Turn
Vehicle
Blazer
4Runner
ML320
Escape
Handwheel Input
(degrees)
401
354
310
287
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NHTSA Fixed Timing Fishhook(Symmetric)
Vehicle
Blazer
4Runner
ML320
Escape
Handwheel Input
(degrees)
326
287
252
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NHTSA Roll Rate Feedback Fishhook(Symmetric)
Vehicle
Blazer
4Runner
ML320
Escape
Handwheel Input
(degrees)
326
287
252
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Nissan Fishhook
•Adjusts timing to maximize roll motion 0
-100
•270 degree initial steer -200
-300
•Vehicle-dependent 40
reversal magnitude (for 20
0
fishhooks) -20
� Blazer = 570 degrees 600
400
200
� Escape = 505 degrees 0
-200
•All rates = 1080 deg/sec 1
0.5•Response-dependent dwell 0
-0.5times -10
0 1 2 3 4 5 6 7 8 Time
0 1 2 3 4 5 6 7 8 Time
0 1 2 3 4 5 6 7 8 Time
1 2 3 4 5 6 7 8 Time
� Iterative determination
Han
dwhe
el (
deg)
R
oll
Rat
e (d
eg/s
ec)
Han
dwhe
el (
deg)
AY
(g)
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Closed-loop, Path-Following Lane Changes
Consumers Union Short Course
ISO 3888, Part 2 Course
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Ford PCL LC
• Comprised of a suite of closed-loop paths (double lane changes)
• Data is processed to remove driver effects and facilitate comparison at a constant severity � All vehicles taken to follow the same path� All vehicles subject to the same lateral
acceleration demands
• Test output is an overall dynamic weight transfer metric
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Ford PCL LC
Full Lane Lane and a HalfHalf Lane
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Comments Based on the Phase IV Rollover
Resistance Maneuvers
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NHTSA J-Turn
• Lowest speed of two-wheel lift is metric • Uses Programmable Steering Controller • Simple step-steer (one cycle) • Handwheel magnitude dependent on
vehicle response
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J-Turn with Pulse Braking
• Lowest speed of two-wheel lift is metric • Uses Programmable Braking and Steering
Controller • Addition of Braking Controller makes
maneuver substantially harder to perform • Timing of brake pulse dependent on vehicle
response (Roll Rate Feedback)
• Results significantly influenced by whether vehicle has working ABS
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Fixed Timing Fishhook
• Lowest speed of two-wheel lift is metric • Dwell time independent of vehicle response • Handwheel magnitudes dependent on vehicle
response • Handwheel inputs within ranges established
during ISO and CU double lane change testing
• Timing may be better for one vehicle than another
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Roll Rate Feedback Fishhook
• Lowest speed of two-wheel lift is metric • Handwheel magnitudes dependent on vehicle
response • Handwheel inputs within ranges established
during ISO and CU double lane change testing • Dwell time also dependent on vehicle response • Timing should no longer favor one vehicle over
another
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Nissan Fishhook
• Lowest speed of two-wheel lift is metric • Iterative procedure requires additional testing
time • Large number of tests required many tire
changes (to reduce tire wear concerns) • Reversals are harsh; increases steering
machine wear
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Ford Path Corrected Limit Lane Change (PCL LC)
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Ford PCL LC
• Metric Dynamic Weight Transfer at 0.7 g based on one of four standard paths (DWTM)
• Method removes driver dependence by normalizing data
• Extra tire testing required (tire measurements) • Concerns about 0.40 second window used for
metric calculation (mitigates dynamic weight transfer observed)
• Metric now measured during tests performed with a driving robot
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ISO 3888 Part 2 Double Lane Change
• Suggested rating metric is maximum achievable “clean” run speed � “Clean” run � no cones struck/bypassed
• Test driver generated steering inputs • Not as repeatable as programmable
steering controller inputs • Tests are straightforward to perform • Course adapts to vehicle width
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Consumers Union Short CourseDouble Lane Change
• Suggested rating metric is maximum achievable “clean” run speed � “Clean” run � no cones struck/bypassed
• Test driver generated steering inputs • Not as repeatable as programmable steering
controller inputs • Tests are straightforward to perform • Course does not adapt to vehicle size
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Open-Loop Pseudo-Double Lane Change
• Uses programmable steering controller • Having three major steering moves slightly
degrades repeatability • Straight-forward to perform • Uses programmable steering controller • Additional development required
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Reporting of Phase IV Findings
Draft of Phase IV NHTSA Technical Report has been written � Reviews in progress � Anticipated release late Spring ‘02
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Phase V Research
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Phase V Overview
• Investigate potential use of a centrifuge • Improved test equipment � Alternative outrigger development � Quantification of two-wheel lift
• Resolution of existing matters � Cold and hot weather testing � Surface effects testing
• Finalize methodology for Phase VI � Loading
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Centrifuge
• Metric could be lateral acceleration at wheel lift or weight transfer
• Quasi-static test • May be demonstrated by NHTSA using a
NASA Facility
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Outrigger Development
•Reduce effects of outrigger installation without compromising driver safety
•Use wheel load transducers to evaluate dynamic load transfer and cornering forces
•Compare three designs� Existing VRTC Design
� Aluminum � 78 lbs per outrigger
� New VRTC Design � Titanium � 68 lbs per outrigger
� Carr Engineering � Carbon fiber � 58 lbs per outrigger
•Testing complete
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Carbon Fiber
•Manufactured by Carr Engineering •Light weight (58 lbs) •Strong •Expensive ($25k / set)
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Titanium •Designed at VRTC using finite element analysis •Light weight (68 lbs) •Less roll inertia than aluminum or carbon fiber •Strong •1/3 cost of carbon fiber •6Al-4V a common Ti alloy •Low-mu hemispherical skid pads replace heavier casters
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Quantification of Two-Wheel Lift
•Objective methodology required •Laser-based height sensors on each wheel� Eliminates video data analysis subjectivity
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Cold and Hot Weather Testing
• Will research the effects of temperature extremes on dynamic rollover propensity
• All testing to be performed at TRC • Cold weather tests performed during January ‘02 • Hot weather tests to be performed Summer ‘02
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Surface Effects Testing
• Determine effects of different test surfaces on dynamic rollover propensity
• Testing performed in Arizona � DaimlerChrysler Arizona Proving Grounds (APG) � GM Desert Proving Grounds � Performed with the Blazer and 4Runner
• Testing complete • Results from Arizona will be compared with
those produced at TRC
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Phase VI
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Phase VI Overview
•Maneuvers based on Phase IV findings
•Three load conditions
•Titanium outriggers
•26 Vehicles
•Will include a wide range of make/models for which state rollover rate data is available
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