Water influence on skid resistance Standardisation: input of the HERMES programme Research Director LRPC de Lyon France
Presentation outline Water influence on skid resistance - influence of the surface (texture, irregularities) - influence of the tyre (compound, tread depth) - input of VERT project and French research -on results - on modelling How to harmonise the skid resistance measurements - standardisation aim - input of HERMES project
Water has to be drained by the surface 25 mm And also by the tyre
Water effect on road surface Section where the superelevation sense changes Rutting Longitudinal irregularities -Surface irregularities : Water depth up to a few cm - Without surface irregularities: the most probable situations Water depth from 0.5 to 1 mm
Tyre tread depth influence: 1 mm water depth New tyre (8 mm) 50 km/h 70 km/h 90 km/h Worn tyre 50% Worn tyre minimum (1.6 mm)
Tread depth influence SD at 120 km/h 110 m New tyre (8 mm) 2 cm 176 m Worn tyre (mini 1.6 mm) Harsh smooth surface (MTD 0.60 mm SFC=0.90) SD at 120 km/h 112 m 800 m
Vehicle-Road-Tyre Interaction in Potential Dangerous Situations: Results of VERT Project VEHICLE TYRES VERT DRIVER ENVIRONMENT ROAD
VERT Project Partners Pirelli Tyres (IT, Tyre Manufacturer) Nokian Tyres (FI, Tyre Manufacturer) Florence University (IT, Education) VTI (SE, road/automotive consultancy) TRL (UK, Road Institute) CRF (IT, Car Manufacturer) Darmstadt University (DE, Education) Porsche (DE, Car Manufacturer) Helsinki Univ. of Technology (FI, Education) CETE (FR, Road Institute)
VERT Project (Nov. 97-Feb 01) VEhicle-Road-Tyre interaction: Development of an integrated full tyre- vehicle-driver model suitable for simulations of potentially dangerous conditions (presence of water, ice, snow, suddenly changing friction etc.) Devices available Test sessions Modelling activity Simulations and classification of dangerous conditions
Development of new measuring devices: Nokian Tyres vehicle
Development of new measuring devices: VTI s vehicle
Other measuring devices CETE Adhera device Darmstadt trailer TRL ASTM Trailer Pirelli trailer
French Device used to measure BFC C 35 LFC = f(slip %) Speed from 20 to 100 km/h Tyres from 145x13 to 245x19 Loads from 2000 N to 5000 N
VERT Tests Goal: To understand the variations of tyre braking performances caused by: Tyre properties Size & type Tread depth (Tread compound) Testing conditions Device Surface Speed Peak value (µ) Stiffness (K) Slide value Slip percentage at peak (x peak )
VERT Tests Surfaces Wet / Dry asphalts (5 types); water layers: 1-81 8 mm Snow (3 types) Ice (4 types) Speeds from 20 to 100 Km/h Vertical loads from 2000 to 5000 N (2 or 3 loads each test)
Tyres Summer: VERT Tests 175/65 R 14 S 195/65 R 15 S 225/45 R 17 S Winter: 175/65 R 14 W (*) 195/65 R 15 W (*) 225/45 R 17 W (*) with and without studs 99 800 readings were made during the test programme.
The French LCPC Nantes Centre
The two surfaces tested by CETE: Asphalt Concrete 0/10: -ETD = 0.60 mm -SFC = 0.67 Very Thin Asphalt Concrete 0/6: -ETD = 0.90 mm -SFC = 0.62 25 cm 10 cm
Tyre-road skid resistance evolution during braking or Relationship skid resistance/slip ratio Skid resistance µ Measures C35 F f Longitudinal ADHERA Measures Transversal Free Wheel 0% Slip Anti locking system 15% slip Locked wheel 100% slip % slip
Raining consequences on tyre-road skid resistance water depth = 1 mm; tread depth = 2 mm AC 0/10 ETD = 0.60 mm 110 100 90 80 70 60 50 40 BFC x100 Speed km/h 20 0 30 40 32 38 42 48 52 56 60 64 68 72 76 80 84 88 92 96100 50 60 70 80 90 0 4 8 12 16 20 24 28 % slip 30 20 10
1 mm water depth 3 mm AC 0/10 ETD = 0.60 mm AC 0/10 ETD = 0.60 mm Tyre with 2 mm tread depth 30 50 speed km/h 70 52 42 32 24 90 16 8 0 84 76 68 60 % slip VTAC 0/6 ETD = 0.90 mm 92 100 20 10 0 90 80 70 60 50 40 30 120 110 100 BFC x100 30 50 speed km/h 70 52 42 32 90 24 16 8 0 84 76 68 60 % slip VTAC 0/6 ETD = 0.90 mm 92 100 40 30 20 10 0 120 110 100 90 80 70 60 50 BFC x 100 120 120 110 110 100 100 90 90 80 70 60 50 BFC X100 80 70 60 50 BFC x100 40 40 30 50 speed km/h 70 90 0 8 16 24 32 42 52 76 68 60 % slip 84 92 100 30 20 10 0 30 50 speed km/h 70 90 0 8 16 24 32 42 52 76 68 60 % slip 84 92 100 30 20 10 0
Water depth influence : (tyre 195x65R15; TD = 2 mm) AC 0/10 ETD = 0.60 mm SFC = 0.67 VTAC 0/6 ETD = 0.90 mm SFC = 0.62 100 100 BFCx100 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 % slip x100 BFC 80 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 % slip 20 km/h; WD=1 mm 20 km/h; WD=3 mm 80 km/h; WD=1 mm 80 km/h; WD=3 mm
Summer tyres Winter tyres new and worn
Water depth influence AC 0/10 (ETD = 0.60 mm SFC = 0.67) Summer tyre 195x65R15 with 3 tread depth levels: 8, 4 and 2 mm 100 Water depth 1 mm 100 Water depth 3 mm 100 Water depth 8 mm 90 90 90 80 80 80 BFC x 100 70 60 50 40 30 20 10 0 4 mm 2 mm 8 mm 0 20 40 60 80 100 % slip BFC x 100 70 60 50 40 30 20 10 0 4 mm 8 mm 2 mm 0 20 40 60 80 100 % slip BFC x 100 70 60 50 40 30 20 10 0 4 mm 8 mm 2 mm 0 20 40 60 80 100 % slip
Special equipped passenger car; test tyres; test track
Stopping distance measured on wet surface
Tyre C - Deceleration*(-1) : (with ABS and without ABS) 1,2 1,0 0,8 0,6 0,4 0,2 0,0 1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120 127 134 141 148 155 162 169 176 183 190 197 204 g -0,2 Stopping distance (x 20 cm) With ABS Without ABS
% Stopping distance on wet pavement in % (base 100 Pirelli J with ABS) 160 140 120 100 80 60 117 136 102 NOKIAN (A) PIRELLI (C) 131 133 105 96 126 104 139 142 101 101 PIRELLI (D) PIRELLI (E) PIRELLI (F) PIRELLI (G) PIRELLI (H) 137 123 145 100 PIRELLI (I) w PIRELLI (J) 134 With ABS Without ABS
µ moy = M. V 2 2 2d V 2 1 M. A F z + V + B. 1 2 V 2 2 d: braking distance V1: speed at the beginning V2: speed at the end M: vehicle masse Fz: vertical load supported by each wheel A and B: parameters linked to the vehicle
VERT Modelling Tyre B1 B Bm L LP Determination of B1, L1, L, B for the model L1 Consideration of the tyre tyre model Introduction of the critical height hk depending on the tyre parameters Model with two phases - h0 to hv - hv to hr (profile completely filled up with water) h0 hv hr hk wfh road model P3DT MODEL
Developed models in VERT VEHICLE VERT TYRES DRIVER ENVIRONMENT Model to predict the available skid resistance ROAD based on real measurement ( one surface, one speed, one tyre, one water depth) predict the skid resistance which will be available on this surface in different conditions µ locked model µ max. model b 1 CF = b + 0 1+ b.e + 2 (b3 b 4.V) The b coefficients depend on water depth, texture and tyre
The Limnimetre
The rainfall artificial system Low Medium High
Developed models in VERT VEHICLE VERT TYRES DRIVER ENVIRONMENT ROAD Proposed model for water depth above aggregates calculation 0.4 (I * L) h = 0.26 * (ETD ) 0. 3 P 0.4 (ETD ) + 0.30 I = rainfall intensity L= flow length P= most important slope Model to estimate the maximum water depth h 1 = 10 (( L Me / 20 ) 5,8) L Me megatexture indicator in db + h
Conclusions (VERT): Correlations between braking test data and testing conditions On wet Asphalt Important statistical amount of information Definitely clear effect of speed, water film thickness, tread thickness Peak and slide values easier to investigate than stiffness and slip-% % at peak Snow/Ice: Not linear/ simple relations with the testing conditions Weak/ not evident influence of the speed Dramatic influence of the surface and the tyre behaviour
Conclusions: rain effect on skid-resistance Even on low rainfall intensity it is possible to find on a road surface some high water thickness (1 to 3 mm) At high speed, tyre (tread) and macrotexture functions are very important to eliminate this water and keep an acceptable skid resistance level. Between medium (WD 1mm, New tyre, ETD>0.9 mm) and bad conditions (WD 3 mm, Worn tyre, ETD<0.6 mm) stopping distances (locked wheel) can be multiplied by 7! Water depths on road surfaces by rainy time is depending of rain intensity, slope, flow length and macrotexture. To predict water depth and skid resistance some models exist. But, These water depths are more over depending of surfaces irregularities as superelevation sense changes, rutting or megatexture.
HERMES HERMES 2001-2004 Harmonization of European Routine and Research Measuring Equipment for Skid Resistance of Roads and Runways
PIACR SC Committee C1 1992 experiment PIARC report Paris 1995 IFI IRFI ASTM standard E1960-98 European standard project EFI - SRI pren 13036-2 ASTM standard E2100-00 HERMES HERMES
HERMES HERMES working group BRRC DRI CEDEX DWW LCPC TRL Belgium Denmark Spain Netherlands France Great-Britain
HERMES HERMES main objective Apply and improve, if possible, the CEN standard for calibration/verification of skid resistance measurements European devices in using the EFI concept
PIARC simplified Model EFI = A + B*F*EXP[(S 30)/Sp] With: A and B device used depending F, friction coefficient measured S, slip speed used during measurement Sp = 57 + 56*MPD or Sp = 43 + 70*MTD
Experiments organised during the HERMES project 23-25/10/01: Great Britain: 4 devices 29-31/10/01; Netherlands: 3 devices 20-22/11/01: Spain: 4 devices 19-21/03/02: Belgium: 5 devices + 3 26-28/03/02: France: 5 devices 23-25/04/02: Netherlands: 5 devices + 2 01-03/10/02: Great-Britain: 4 devices + 1 08-10/10/02: Belgium: 4 devies + 1 15-17/10/02: France: 6 devices
IMAG (F) ADHERA (F) HERMES ODOLIOGRAPH (B) SKIDOMETRE (NL) SCRIM (SP)
EFI interest: 1,0 Direct comparison Comparison between spanish SCRIM and french ADHERA 0,8 0,6 0,4 0,2 1 Comparison based on EFI 0,0 0,0 0,2 0,4 0,6 0,8 1,0 0,8 0,6 0,4 0,2 0 0 0,2 0,4 0,6 0,8 1
Sp = f(mpd) 700,00 All devices included 600,00 Sp (km/h) 500,00 400,00 300,00 200,00 Sp = 56*MPD+57 100,00 0,00 0,00 0,50 1,00 1,50 2,00 2,50 3,00 3,50 MPD (mm)
Difficulty linked with the devices stability 1,2 F13 compared to F04 for all the test speeds 1,0 0,8 F13 0,6 0,4 Trial 2,3 Trial 3,2 0,2 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 F04
HERMES HERMES Main results: - HERMES confirmed the EFI interest - PIARC model is not enough accurate - The texture influence on friction seems not enough taken into account by MPD (develop other models for Sp than Sp = a+b(mpd) or a(mpd) b ) - The participating devices not enough controlled before the tests - It appears necessary to set out references for such tests - references surfaces (first overview) - reference device (first specifications written)
HERMES HERMES Short term (less than 4 years): Propose a temporary method to allow the device results comparison to a common scale; this method would be used in a first EN standard series; Propose a harmonised procedure to verify the devices quality; Apply this method and this procedure in real conditions to increase the EFI accuracy Launch a feasibility study for reference surfaces.
HERMES HERMES For long term (more than 8 years): Progressively replace the existing devices by the reference device; Adapt or improve the European calibration procedure; Develop a new EN standard (descriptive) for a test method based on the reference device
The end Thank you for your attention