Testing and Understanding of Tire-Road Interaction on Wet Roads Die Reifen-Fahrbahn Wechselwirkung auf nasser Straße messen und verstehen

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1 Bitte decken Sie die schraffierte Fläche mit einem Bild ab. Please cover the shaded area with a picture. (24,4 x 7,6 cm) Testing and Understanding of Tire-Road Interaction on Wet Roads Die Reifen-Fahrbahn Wechselwirkung auf nasser Straße messen und verstehen Dr. rer. nat. Stefan Torbrügge Continental Reifen Deutschland GmbH, Tire Line Development

(24,4 x 7,6 cm) Testing and Understanding of Tire-Road Interaction on Wet Roads Die

2 Agenda Motivation: Driving safety From rubber friction towards understanding of tire wet grip Understanding impact of road wear on wet skid resistance of roads EU wet label testing: Vehicle and trailer based test methods EU wet label testing: Conformity of labeled products Continental AG 2

skid resistance of roads EU wet label testing: Vehicle and trailer based

3 Stop the crash campaign CTF Slide --Volker PARTNERED BY Driving safety is a key vision of Continental The tire is the only part of the vehicle transmitting forces to the road Continental AG 3

4 Braking Distance from 100 km/h [m] Historic Development of Wet and Dry Braking Performance Wet Braking Introduction of Silica Blocked Wheel No ABS / ABS ABS Dry Braking Continuous improvement in stopping distance is driven by: Customer expectation Competition Legislation Various sources, including press tests 1995 Year

Braking Continuous improvement in stopping distance is driven by: Customer expectation

5 Friction Coefficient µ [.] Friction Coefficient µ of Different Road Conditions Wet surface as most critical surface Why spreading of skid resistance of wet tracks so high HYD Dry Wet Snow Ice Friction level used by customer HYD: Hydroplaning 5

6 Agenda Motivation: Driving safety From rubber friction towards understanding of tire wet grip Understanding impact of road wear on wet skid resistance of roads EU wet label testing: Vehicle and trailer based test methods EU wet label testing: Conformity of labeled products 6

wear on wet skid resistance of roads EU wet label testing: Vehicle and

7 vehicle velocity v [km/h] Evaluation of stopping distance Wet braking performance v Stopping distance s distance s [m] Evaluation of stopping distance: s 2 1 v0 2 g s: stopping distance µ : mean tire-road friction coefficient v o : initial speed g = 9.81 m/s 2 7

25 30 35 40 distance s [m] Evaluation of stopping distance: s 2 1 v0 2 g s:

8 Deceleration a [m/s²] Velocity v [km/h] Evaluation of stopping distance Vehicle & wheel dynamics during ABS wet braking ,0 7,5 5,0 2,5 0,0 Wheel slip variation due to active ABS Fahrzeug_Geschw Vehicle velocity Wheel velocity front right Wheel velocity rear right Reifen VR Reifen HR Reifen VL 0-0,5 0 0,5 1 1,5 2 2,5 3 3,5 Time [s] Constant deceleration due to stable ABS working condition a µ g Wheel velocity front left Reifen Wheel HL velocity rear left -0,5 0 0,5 1 1,5 2 2,5 3 3,5 Time [s] 8

Wheel velocity rear right Reifen VR Reifen HR Reifen VL 0-0,5 0 0,5 1 1,5 2 2,5 3 3,5 Time [s] Constant deceleration due to

9 Longituidnal force coefficient µ Longitudinal tire characteristics 1,2 1 0,8 0,6 ABS operating point Compound 1 ABS system operates the tire at a wheel slip for which the maximum forces can be transmitted 0,4 0,2 Measurement at inner drum test Karlsruher Institut für Technologie (Prof. Gauterin) on wet asphalt. v=80 km/h 0 0% 5% 10% 15% 20% 25% Tire slip [.] 9

maximum forces can be transmitted 0,4 0,2 Measurement at inner drum test rig @ Karlsruher

10 Frequency of occurence [%] Wheel slip distribution during ABS braking ABS operating point Characteristic tire slip velocity during braking Tread block dynamics v s Slip-Speed v s [m/s] F friction Simplest system to study tire grip 10

slip velocity during braking Tread block dynamics v s 0 0 1 2 3 4

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13 Rubber Hysteresis Friction Elastic and viscous materials What happens when a solid body is deformed? Elastic body Viscous body F el Energy in = Energy out F Energy in Energy out = 0 Lost Energy = 0 Δx All Energy is lost Δx v v S. Torbrügge, Continental AG 13

Elastic body Viscous body F el Energy in = Energy out F Energy

deformation on rough road F Energy in - Energy out = Lost Energy Δx

14 Hysteresis Friction: Viscoelastic materials In viscoelastic materials energy is partially stored and partially dissipated Hysteresis friction via rubber deformation on rough road F Energy in - Energy out = Lost Energy Δx Hysteresis Finite Element Method (FEM) simulation of rubber road contact and friction 14

15 Agenda Motivation: Driving safety From rubber friction towards understanding of tire wet grip Understanding impact of road wear on wet skid resistance of roads EU wet label testing: Vehicle and trailer based test methods EU wet label testing: Conformity of labeled products Continental AG 15

16 Which track exhibits higher wet skid resistance? Continental AG 16

17 Diversity of track surfaces Characterization of track roughness 130 mm 3D surface texture scan Continental AG 17

18 Diversity of track surfaces Typical pavement textures Rough asphalt Smooth asphalt Smooth concrete Rough concrete Continental AG 18

19 Rail guided wet braking Rail guided aquaplaning Highly reproducible Neglect environmental influences Continental AG 19

20 µ ABS wet [.] Impact of road wear on surface properties Polishing behavior of asphalt track 1 0,9 C3.3 µ-srtt Data Fit: wet ( x) 0 µ-srtt Fit, e x Track wear in tire-road contact leads to drop of road s wet skid resistance 0,8 0,7 Micro-polishing of stone asperities changes track s roughness characteristics 0,6 AIBA wet-braking asphalt test track, identical car & tire Number of wet-brakings reduced hysteresis friction Continental AG 20

skid resistance 0,8 0,7 Micro-polishing of stone asperities changes track s roughness characteristics 0,6 AIBA

surface as most critical surface 1.2 1.0 0.8 0.6 0.4 0.2 0.

21 Friction Coefficient µ [.] Friction Coefficient µ of Different Wet Road Conditions Wet surface as most critical surface HYD Dry Wet Snow Ice Degradation of wet skid resistance not noticable by naked eye during driving! 21

22 Agenda Motivation: Driving safety From rubber friction towards understanding of tire wet grip Understanding impact of road wear on wet skid resistance of roads EU wet label testing: Vehicle and trailer based test methods EU wet label testing: Conformity of labeled products Continental AG 22

23 Methods of measuring EU wet-label braking performance Trailer Test µ Evaluation of µ-slip curve, µ-peak + Vehicle independent tyre test slip[%] - Grip measurement at only one specific 65±2 km/h Stopping Distance Test Vehicle test of stopping distance ++ End-consumer related test, close to reality (real car, real conditions) - Suitable vehicles and rims needed Continental AG 23

Residual stopping distance compared to label A tire [m] Impact of EU-wet label classification on stopping distance Increase in stopping distance in relation to a wet-label class A tire Label class

24 Residual stopping distance compared to label A tire [m] Impact of EU-wet label classification on stopping distance Increase in stopping distance in relation to a wet-label class A tire Label class Residual velocity Remaining stopping distance (80 km/h to stand still) Non-linear increase in stopping distance for lower label classes m to 6 m between label classes! A B C E F Wet-grip label class 24

25 Estimated texture depth [mm] Requirements for wet-label testing 1,2 Track Permissible Range Temperature 1,0 2 C Winter tire 20 C 0,8 0,6 5 C Summer tire 35 C 0,4 0, EU label correction equation: (acc. EC 1222/2009) Friction Level [BPN] [ASTM E ] Tire Temperature [ C] Temperature Correction Tire Wet Grip Index = a. (T T 0 ) + b. 1.0 SRTT SRTT0 Surface Correction 2 S. November Torbrügge 2015 Continental AG 25

Wet Grip Index Wet Grip Index Tire Performances Wet Grip Index depends on surface and temperature Tire A Tire B Grip Level Grip Level Wet braking is

26 Wet Grip Index Wet Grip Index Tire Performances Wet Grip Index depends on surface and temperature Tire A Tire B Grip Level Grip Level Wet braking is significantly influenced by surface and temperature Although corrections have been applied, EU-Label classification is still depending on test conditions 26

27 Agenda Motivation: Driving safety From rubber friction towards understanding of tire wet grip Understanding impact of road wear on wet skid resistance of roads EU wet label testing: Vehicle and trailer based test methods EU wet label testing: Conformity of labeled products Continental AG 27

28 EU Wet Label Review Evaluation of press test results ADAC/ ÖAMTC ADAC Motorwelt 09/

29 EU Wet Label Review Evaluation of press test results - AutoBild 50 products tested under comparable conditions. Premium Ultra Cheap representing complete market

30 EU Wet Label Review Evaluation of press test results AutoBild Stopping distance 80-0 km/h [m] AutoBild Winter Tire Test 2015 ± 15% ± 7 m ContiWinterContact TS 850 E C B

31 EU Wet Label Review Evaluation of press test results Auto Bild Stopping distance km/h [m] ± 19% ± 12 m ± 12% ± 6 m ± 5% ± 3 m AutoBild Summer Tire Test 2015 ContiPremiumContact 5 ± 17% E C B A

32 EU Label Performance Spotcheck by Cotinental Wet Label Summer Passenger Car Tires Company 1 Company 2 Company 3 Company 4 Company 5 Company 6 Company 1 Company 8 Company 9 Company 10 Company 11 Company 12 Company 13 Company 14 Tested Better Than Declared Tested = Declared Product did not meet declared label, minor deviations Product did not meet declared label, significant devitations 32

33 EU Label Performance Spotcheck by Continental Wet Label Winter Passenger Car Tires Company 1 Company 2 Company 3 Company 4 Company 5 Company 6 Company 7 Company 8 Tested Better Than Declared Tested = Declared Product did not meet Within declared Tolerance label, minor deviations Product did not meet declared label, significant devitations Company 5 33

34 Conclusions The tire is an important contributor to driving safety, especially on low-µ wet roads Road wear leads to micropolishing of stone asperities and drop of wet skid resistance EU wet label reflects the importance of wet braking performance for driving safety EU wet label procedure still results in too large spread of results There is (strong) indication that tires are on the market which do not (fully) comply with the EU wet label marking 34

35 Bitte decken Sie die schraffierte Fläche mit einem Bild ab. Please cover the shaded area with a picture. (24,4 x 7,6 cm) Thank you very much for your attention! Vielen Dank für Ihre Aufmerksamkeit! Dr. rer. nat. Stefan Torbrügge Continental Reifen Deutschland GmbH, Tire Line Development

Continental SportContact 6 Technical Highlights

Continental SportContact 6 Technical Highlights Bitte decken Sie die schraffierte Fläche mit einem Bild ab. Please cover the shaded area with a picture. (24,4 x 7,6 cm) Continental Technical Highlights www.continental-tyres.com Marketing Market Development