Analysis of the Influence of Driving Dynamic Parameters on Tire Marks

1. Gunther Seipel , Prof. Dr. Hermann Winner, TU Darmstadt Dr. Frank Baumann, Ralf Hermanutz, Daimler AG Analysis of the Influence of Driving Dynamic Parameters on Tire Marks

2. Overview • Motivation • Objectives and Methodology • Model for the Emergence of Tire Marks • Influencing Driving Dynamic Parameters • Experimental Results • Further Steps • Summary and Outlook

3. Motivation • Tire Marks in Accident Reconstruction • Tire marks provide evidence regarding • Amount of speed reduction • Trajectory of vehicles • Place of collision • Curving speed • Vehicle defects • … Tire marks are of particular importance to clarify the circumstances leading to an accident Pictures: http://www.unfallaufnahme.info

4. Motivation • Changes in Tire Mark Characteristics due to Changes in • Tires • Wider Dimensions • New Types (e.g. RoF, Low Rolling Resistance) • Chassis • Weights • Suspension • … • Chassis Control Systems • Improvementsof ABS • New Systems (e.g. ESP) • … ? Validity of Application of Conventional Reconstruction Methods • Main Questions • Under which conditions do tire marks occur? • How do driving dynamics parameters influence the visibility of tire marks? • How do different types of tires affect the emergence of tire marks?

5. Objectives Vehicle Driver Driver Assistance Systems ExternalForces TireSpeed, Longitudinal and Lateral Slips • Evaluation of the influence of superior processes by analysis of influence of basic driving dynamic parameters TireForces Tire Road Tire Mark Focus of Research

6. Methodology • Top-Down Approach Model of Fundamental MechanismsforEmergenceofTire Marks Identificationof Relevant Driving Dynamic Parameters Experimental Analysis of Parameters on a Mono-Wheel Transfer ofResults on Passenger Car

7. Model for the Emergence of Tire Marks • General Assumption of Two Main Mechanisms: • Abrasive tire wear due to sliding friction (tire side) • Bleeding of bitumen due to frictional heating (road Side) Tire Properties TireHeating Tire Side γ Friction energy per length is of key significance for the emergence of tire marks! Tire Mark Intensity v Road Side for asphalt roads Road Properties Road Heating

8. µ µ=cλ∙λ Model for the Emergence of Tire Marks µmax µ-λ-curve µslide • Calculation of Friction Energy per Length • Assumptions: • Friction in the contact patch between tire and road surface occurs only for sliding friction deformation slip area slide slip area λ 0 % 100 %

9. Model for the Emergence of Tire Marks • Calculation of Friction Energy per Length • Assumptions: • Friction energy per length is the product of the resulting friction force and the resulting friction path per travelled distance • Resulting Friction path between tire and road per travelled distance is equal to the resulting slide slip

10. Model for the Emergence of Tire Marks • Identification of Relevant Driving Dynamic Parameters • Wheel load, longitudinal slip and slide slip angle determine the amount of friction energy per length • Hypotheses: • No tire marks occur for pure deformation slip, i.e. • The intensity of a tire mark increases with increasing friction energy per length (under constant boundary conditions) • The intensity of a tire mark depends on the amount of friction energy per length independent of the varying parameter

11. Experimental Analysis • Testing Tool • Tire Measurement Trailer PETRA (Personen-wagen-Reifen-Traktions-Messanhänger) • Originally built for the µ-slip-analysis of car and light truck tires with varying: • Tire types • Pavement textures and intermediate mediums • Speeds • Wheel loads • Longitudinal and lateral slips • Camber angles

12. Experimental Analysis • Tire Measurement Trailer PETRA • Components Gearbox (hidden) Hydraulic tank Analyzer unit Reference wheel Regulator (hidden) Oil cooler Hydraulic pump (hidden) IR temperature sensor Measuringrim Accumulator Slip angle adjustment Measurement wheel Correvitsensor

13. Experimental Analysis • Tire Measurement Trailer PETRA • Functional principle Proportional valve • Measurement wheel is linked to axial piston pump via gearbox • Pump conveys oil against a regulator • Generated pump torque (by measurement wheel) depends on pump speed (=wheel speed via gearbox) and oil delivery volume • Oil delivery volume is adjusted using a proportional valve • Equilibrium of brake and pump torque leads to stationary working points with constant longitudinal slip Regulator Reference wheel Hydraulic axial piston pump Cooler Measurement wheel Gearbox stationary working points transponedµ-λ-curve characteristic pump curve

14. Experimental Analysis Assessment of Visibility • Subjective assessment of tire mark on a scale from 0 (no mark) to 10 (clearly recognizable)* *Cf. Grandel, J., 1989

15. Experimental Analysis • Testing Ground • Former airfield with asphalt pavement

16. Experimental Analysis • Test Procedure • Generation of tire mark within a defined area • Marking and documentation of tire mark PETRA

17. Experimental Analysis • First Results • No visible tire marks for pure deformation slip • Tires show increasing intensity with increasing friction energy • The amount of friction energy per intensity and beginning of visibility differs between different tire types

18. Experimental Analysis • First Results • Restrictions: • Large scattering of intensity values mainly due to subjective assessment of visibility and environmental influences (e.g. lighting conditions, angle of view, individual perception) • Tire marks for the same values of λ, α andFz not always reproducible

19. Further Steps • Requirements for Further Investigation • Development of an objective method for the assessment of tire mark intensity, which is robust against environmental influences • Development of a method to determine the “tire marking sensitivity” of different combinations of tire and road surface Tire Properties TireHeating Tire Marking Sensitivity Tire Side γ Tire Mark Intensity v Road Side for asphalt roads Road Properties Road Heating

20. Further Steps • Requirements for Further Investigation • Development of an objective method for the assessment of tire mark intensity, which is robust against environmental influences • Development of a method to determine the “tire marking sensitivity” of different combinations of tire and road surface • Approach: Determination of sensitivity with help of a mobile testing facility for tire tread elements which allows for indoor and outdoor use under very controlled conditions

21. Possible Applications • Backward Calculation • Forward Calculation Intensity of tiremark (crashscene) Tiremarkingsensitivity Frictionenergy Determination with mobile testing facility at crash scene Output parameters from driving dynamics Simulation Beginning, intensity, … Calculation of frictionenergy Tiremarkingsensitivity Visibility of tiremark

22. Summary and Outlook • A concrete model was presented showing the key significance of dissipated friction energy per length for the emergence of tire marks • Longitudinal slip, tire slip angle, and wheel load have been identified as relevant driving dynamic parameters, determining the amount of this energy • Experimental results basically agree with the model description • Results additionally show a high influence of tire and road specific properties (tire marking sensitivity) on the intensity, and environmental influences on its assessment • Requirements for further investigation: • Development of an objective and robust method for the assessment of tire mark intensity • Development of a method for the determination of the tire marking sensitivity of different tire/road combinations