SECURITY & ADHERENCE TESTING Joël Foucard

Michelin proprietary informationMercedes-Michelin meeting , 08 June 2004 , Ladoux

SECURITY & ADHERENCE TESTING

Joël Foucard


ROAD CHARACTERISTICS

ADHERENCE MECHANISMS

ACCIDENT ANALYSIS

MICHELIN TEST TRACKS

ADHERENCE AND SAFETY

WET GRIP REGULATION

EURONCAP

ADHERENCE TESTING : MICHELIN STRATEGY


PARAMETERS :

ROADS CHARACTERISTICS

Microtexture :

0,1µm to 10µm height

Macrotexture :

10µm to 1mm height


Sand Depth (mm) : mean texture depth

Direct measurement : from diameter of sand mark


MACROTEXTURE :

Indirect measurment : computation from laser texture measurement



MICROTEXTURE : SCRIM vehicle : transversal friction coefficient (CFT) on wet road with a motorcycle tire at 20 deg angle


0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5

HS (mm)

CFT

-40 -30 -20 -10 0

0

10

20

30

40

50

60

70

80

90

100

-25

-20

-15

-10

-5

0

0,1 0,3 0,5 0,7 0,9 1,1 1,3 1,5 1,7 1,9 2,1 2,3 2,5 2,7 2,9 3,1

1 5 3 1

1 12 8 5 3

0

0

13 9 5 310 6 3 2

3 1 1 1

1


FRENCH ROADS DISTRIBUTION :

Microtexture : CFT

Macrotexture : Sand Depth

Data from transport department :

CFT distribution is confidential : cannot be given

with this detail level



FRENCH ROADS DISTRIBUTION :

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5

HS (mm)

CFTMicrotexture : CFT


Data from transportation ministry :




ACCIDENT ANALYSIS



WET GRIP REGULATION

EURONCAP




MECHANISMS :

Hydro-planning X

Visco-planning X

Indentation X X

Adhesion X

Main mechanisms only :

Area1 Area2 Area3 Area4

Water thickness >1mm 10 µm <<Indenter height

0

Area 1Area 2Area 3Area 4



HYDROPLANNING : Phenomenon :

-Loss of contact due to hydrodynamic effects , dependent on speed, pressure , water height , pattern depth

Key actors :

- Tire :

- Tread pattern

- Pressure map in contact patch

- Road :

- Macrotexture and banking

- Absence of ruts

V2ρ21Pressure



VISCOPLANNING :

2

2 1i

f

f h

h

h

S

pKt

- Squeezing of water between a flat surface and rubber due to water viscosity, as soon as the layer thickness is < 10 µm

- Tire :

- Eliminate water

- Create high local pressure

- Road :

- Microtexture to puncture the water film

goodBad

Phenomenon :

Key actors :

hf : final height

hi : initial height

S : surface

P : pressure

: fluid viscosity



INDENTATION :

- On the top of any indenter , delay between stresses and strains due to rubber hysteretic losses .

- Appears at all scales of indenters sizes and associated excitation frequencies

- Tire :

- Viscoelastic properties under high frequency (104 to 107 Hz) and high strain

- Road :

- Texture on a large band of indenter sizes and associated excitation frequencies

Phenomenon :

Key actors :

Calcul Gomsol D sur un profil extrait d'un fichier .ima : indentation

-5

-4

-3

-2

-1

0

1

2

0 5 10 15 20 25 30

X

Z

Profil Gomme

Rubber

Ground



BRAKING DISTANCE ON WET ROAD :

- Dominant mechanisms under these conditions :

-Hydroplanning is neglectable

-Viscoplanning is dominant on low-micro & low-macro surfaces . Its impact may be emphasised on dirty/polluted roads

-Indentation is dominant on almost all clean roads

Visco-planning on clean roads

Visco-planning on dirty roads

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5

HS (mm)

CFT

Conditions : 80 to 10 km/h ; Water thickness = 1 mm ; New tire


No µ loss due to Hydro

Significant µ loss due to Hydro

function of tiresize and wear level


BRAKING DISTANCE ON WET ROAD : Max rain intensity (2% of the total rain time) :

- Measurement of water height above the indenter summit (PREDIT program)

0

5

10

15

20

25

30

0,1 0,3 0,5 0,7 0,9 1,1 1,3 1,5

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

HS (mm)

HS (%) water depth (mm)

1mm is a maximum value for a good road . More than 1mm occurs in pools and ruts


0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

40 60 80 100 120 140 160

wh=0,2 - new

wh=1,0 - new

wh=0,2 - worn

wh=1,0 - worn

Speed (km/h)

Friction coeff , µmax


BRAKING DISTANCE ON WET ROAD : Conditions : speed , tread pattern depth , water height

Hydroplanning is a significant mechanism in worn tires braking distance




ACCIDENT ANALYSIS



WET GRIP REGULATION

EURONCAP



GLOBAL FIGURES : FRANCE

ACCIDENT ANALYSIS

- INRETS DATA ON 2001 PERIOD

- Focus on fatalities

- Total of 7720 people killed

Pedestrian 10,1%

Cyclist 3,1%

Cyclomotorist 5,5%

Moto 13,1%

PC 64,7%

Trucks (1) 1,7%

Other 1,7%

Total 100%

Highway 6,4%

Regional roads 24,2%

Local roads 53,8%

Other 15,6%

Urban areas (2) 25%

country 75%

(1) : Trucks

= 5,2% of traffic

= 5% of injury accidents

= 13% of fatalities

(2) : Urban areas :

= 1/4 of fatalities

= 2/3 of injury accidents

Who Where Note


TYPE OF ACCIDENT :

ACCIDENT ANALYSIS

Longitudinal loss of control : 32%Lateral loss of control : 55%

Location of killed people

Type of accident

Circonstances

Trucks

1,3%

Back end Collisions:

4,4%

2 Wheels

20,8%Pedestrians

11%

Head on collisions:

19,3%

Side collisions

17,7%

Isolated veh. w/o pedestrian

35,3%

Isolated veh with pedestrian

10,1%

P.Cars

64,3%

Trees:

9,9%

Enbankment , Ditc ,..

7%

Wall , Bridge, ..

5,2%

Post:

3,4%

Rails:

2,8%

Intersections:

15,9%Passing :

?%

Lane wandering :

?%

Inter vehicle distance:

?%

Other

13,2%


RAIN CONDITION :

Weather condition Fatality %

Normal 75,4%

Rain 13,6%

Snow-Hail 0,9%

Fog 1,2%

Others 8,9%

ACCIDENT ANALYSIS

-Average rain duration in France : 9,3%

-Known rain effects :

-No pedestrian and few cycles and motorcycles

-Sensible reduction of passenger cars traffic

Estimation of specialists : 3 times more accident / km in rain condition than in normal dry condition


DAMP ROAD CONDITION :

Ground condition Fatality %

Dry 76%

Wet 20,6%

Deep water 0,2%

Flooded 0

Snow 0,5%

Ice 1,4%

Others 1,4%

ACCIDENT ANALYSIS

-Damp surface condition : rain condition + drying time

-Depending on sources , damp condition = 25% to 40%

As recorded in police report , do not take into account very thin layers of water such as :

-Moisture retained by road salt during winter

-Morning dew

Generic data files do not allow to estimate the severity of damp condition versus dry condition


ROAD WEAR :

ACCIDENT ANALYSIS

The Accident risk level increases as the µ level decreases

0

2

4

6

8

10

12

14

16

18

20

0,25 0,3

0,35 0,4

0,45 0,5

0,55 0,6

0,65 0,7

0,75 0,8

0,85 0,9

0,95 1

0

1

2

3

4

5

6

7

8

%

Car Page et Buta

Car Gandhi

Car Schlösser

Car Rizenberg

Car Harwood

CFT

Car (Risk increase coefficient)% distribution CFT

µ=0,6

Impact on accidents in wet condition


ROAD POLLUTION :

ACCIDENT ANALYSIS

35

6

8 7

14

92

10

1211

0%

5%

10%

15%

20%

25%

0% 5% 10% 15% 20% 25%

Rain

Accidents under rain

-10 years statistics : rain is more severe in fall than in the rest of the year .

-First rain after a long period of dryness is more severe because it makes a viscous mixture with chemicals (gasolin , grease , vegetal origin , …) deposited in the bottom of texture

Viscoplanning is extremely unlikely on clean road but may have a significant action on polluted roads

Impact on accidents in wet condition


ACCIDENT ANALYSIS

CUSTOMER NEED VS AVAILABLE POTENTIAL

A margin is available on dry roads for emergency manoeuvers . But there is no such margin on lowest grip wet roads nor in winter .

µ coefficient

1,0

0,8

0,6

0,4

0,2

0

Dry Wet Winter

Range of adherence used by customers in normal conditionsRange of adherence used by customers in normal conditions

Range of max potential offered by tire/roadRange of max potential offered by tire/road

New road

Worn road

Polluted roadSnow

Ice




ACCIDENT ANALYSIS



WET GRIP REGULATION

EURONCAP




PASSENGER CAR TRACKS CHARACTERISTICS :

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5

HS (mm)

CFTMicrotexture : CFT


L1

L2

L3 L4T1

T2 T3

Longitudinal (braking)

-L1 : min. threshold

-L2 & L3 : axes of product improvement

-L4 : research only

Transversal

- T1 : circular ring , min. threshold

-T2 : circular ring ,axis of product improvement

-T3 : wet handling track , axis of product improvement

Michelin test requirements adapted to our understanding of customer risks




ACCIDENT ANALYSIS



WET GRIP REGULATION

EURONCAP




ADHERENCE PERFORMANCE BUILDING :

PneumaticBrakes + Chassis

ElectronicSystems

Customer Reaction

Ground contact Potential

Fraction of potential use

Braking potential Fraction of potential use

Road & Weather conditions

X

X



ABS IMPACT ON SAFETY :

GM study , SIA Paper N° 98-S2-0-12

-Scope :

-7 GM vehicles models equipped w / wo ABS

-5 states in USA

-1 year time period

-Main résults on casualty accidents :

-No significant impact on overall number

-Slight increase on dry road due to speed increase with ABS , increase of accident severity

-12% reduction on wet roads

-22% reduction of accidents involving pedestrian

Improving braking potential pays more on wet than on dry roads



ESP IMPACT ON SAFETY :

Swedish National Administration , Paper N°261

-Scope :

-Sweden 2000-2002

-MB, BMW, Audi-VW, w/wo ESP . ABS on all vehicles

-1 year time period

-Main résults on casualty accidents :

-22% reduction on overall number

-9% reduction on dry roads

-31% reduction on wet roads

-38% reduction on snow & ice

Improving braking potential pays more on low traction roads than on high traction roads




ACCIDENTS ANALYSIS



WET GRIP REGULATION

EURONCAP



2 APPROVED METHODS • Method using a standard vehicule : braking distance• Method using a trailer : µ(G) curve

EVALUATION IN RELATIVE• Relative performance basis : comparison to a reference tyre : SRTT E1136 (195/75R14)

TRACK GENERAL SPECIFICATION• Sand depth : 0.7 + 0.3 mm• BPN : 50 + 10

TEST TEMPERATURE• Wetted surface temperature within 20°C +/- 15°C• Temperature variation during test < 10°C

WET GRIP REGULATION


• Standard model passenger car , 4 wheel ABS braking , suitable to accept a wide variety of tire sizes

• Static tyre load : from 60% to 90% of the tyre load capacity

• Measurement of the average deceleration of a vehicle between two given speeds

• Initial speed : 80 km/h

• Final speed : 20 km/h

• Water depth : flooded between 0,5 and 1,5 mm

WET GRIP REGULATION

VEHICLE METHOD :


C1 C2 ….Ck : control tyres

x x x x x

xx

x x

xx x x

x x x x

Reference tyre

x x x x xx x x

x x

WET GRIP REGULATION

VEHICULE METHOD :

• Unique reference tire

• Use of control tire to deal with tire size differences

• (Test/Reference) = (Test/Control) x (Control/Reference)

Vehicle 1

Vehicle 2


WET GRIP REGULATION

TRACK SPECIFICATION :

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5

HS (mm)

CFT

Norme wet grip

0

10

20

30

40

50

60

70

80

90

100

-100

-90 -80 -70 -60 -50 -40 -30 -20 -10 0

Microtexture : CFT

Macrotexture : Sand DepthMicrotexture : BPN40 to 60 0,4 to 1,0




ACCIDENTS ANALYSIS



WET GRIP REGULATION

EURONCAP



EURONCAP

Wet adherence issue

The risks from our understanding of EuroNCAP project :

TRACK SPECIFICATION

Macrotexture

(Sand Depth)

Microtexture

(BPN)

Wet grip regulation

Stone mastic Asphalt

Basalt

Excellence area of stiff tread pattern

Excellence area of soft tread pattern (like winter tread pattern)

If the surface choice is confirmed (against the pneumatic industry expertise) , this could handicap the development of the best solutions for low adherence roads


The track surface evolution is not compatible with absolute braking distance ranking

EURONCAP

ABSOLUTE RANKING

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SECURITY & ADHERENCE TESTING Joël Foucard