BACHELOR'S THESIS Method Development for Road Grip Correlation between Different Force Based Sensors Marcus Lundholm Per Wallgren 2016 Bachelor of Science in Engineering Technology Automotive Engineering Luleå University of Technology Department of Engineering Sciences and Mathematics Abstract This thesis presents an experimental approach on how to evaluate the corre- lation between different force based road grip sensors. Road grip sensors are commonly used to evaluate road safety conditions, eliminating uncertainty for road maintenance. Today, different technologies has been developed to measure the interactions between tire and road to generate a friction value that describes the amount of grip a tire has on the measured surface. Differ- ent systems generates different friction values, thus depending on the mea- surement system, the road maintenance requirement specifications varies. A correlation between the systems is therefore important to enable specification translations for nations in the Nordic region. The Norwegian Public Road Administration, NPRA has three types of sys- tems that use the technology of longitudinal slip to measure the friction value, with a pulse braking measurement tire. While Lule˚aUniversity of Technol- ogy has a different system, RT3 Curve, that use the technology of lateral slip, with two toe in set tires causing a slip-angle, forcing the measurement tires to slide continuously. Tests were executed in Røros, Norway for two days during winter conditions. The objectives were to investigate if there was any correlation between the systems and the main depending factors. The results showed that on compact snow and sand covered roads the NPRA systems measured approximately 70% of the RT3's measured value. A linear regres- sion showed that 77% of the NPRA systems variations can be explained by the variations of the RT3 system. The main depending factors are the differ- ent measurement tires and the sample-rates. Future studies are necessary to cover more different road surfaces. i ii ABSTRACT Acknowledgements This thesis work was performed at Lule˚aUniversity of Technology and fin- ishes our studies in the B.Sc. Programme in Automotive Engineering. The journey of becoming automotive engineers has been both challenging and fun. We sincerely thank our supervisor Johan Casselgren at the university for being very helpful throughout the whole project. He has inspired us by shar- ing his experiences. We also want to thank B˚ardNonstad and Bjørn Ove Ofstad at the Norwegian Public Road Administration for welcoming us to Røros and making this project possible. iii iv ACKNOWLEDGEMENTS Contents Abstracti Acknowledgements iii 1 Introduction1 1.1 Background............................1 1.2 Goal and objectives........................2 1.3 Project boundaries........................3 2 Theory5 2.1 Friction..............................6 2.2 Tire properties..........................8 2.2.1 Construction.......................8 2.2.2 Tread geometry...................... 12 2.2.3 Rubber hardness..................... 14 2.3 Tire Kinematics.......................... 16 2.4 Longitudinal Slip......................... 17 2.5 Lateral Slip............................ 20 3 Equipment 23 3.1 NPRA............................... 23 3.1.1 OSCAR.......................... 23 3.1.2 ROAR Mk III....................... 24 3.1.3 ViaFriction........................ 26 3.2 RT3 Curve............................. 27 v vi CONTENTS 4 Measurements 31 4.1 Røros 2016-02-02......................... 32 4.1.1 1km Measurement on Fv541............... 32 4.1.2 Long Drive around Aursund............... 33 4.2 Røros 2016-02-03......................... 34 5 Methodology 37 5.1 Data Management........................ 37 5.1.1 Import........................... 37 5.1.2 Modification........................ 38 5.1.3 Visualization....................... 41 5.1.4 Analysis.......................... 41 6 Results and Discussion 43 6.1 1 km Measurement on Fv541.................. 44 6.2 5 km Measurement on Fv31, Fastsand............. 50 6.3 Correlation............................ 56 6.4 Discussion............................. 60 7 Conclusions 63 Bibliography 63 A Appendix 69 A.1 1 km measurement on Fv541 in lane 1............. 69 A.2 1 km measurement on Fv541 in lane 2............. 74 A.3 5 km measurement on Fv31 in lane 2.............. 84 List of Figures 2.1 Friction is very complex and multidimensional [1]........5 2.2 Static and dynamic friction [2]..................6 2.3 Macroscopic contact between tire and road...........7 2.4 Road contamination that prevents intermolecular bonding [3].7 2.5 Brush model [4]..........................8 2.6 Bias-ply/cross-ply construction [5]................9 2.7 Radial construction [5]....................... 10 2.8 Example of friction in relation to inflation pressure for a ASTM 1136 SRTT radial tire [6]..................... 11 2.9 Example of friction in relation to inflation pressure for a Goodyear Eagle LS radial tire [6]....................... 12 2.10 OSCAR's winter measurement tire ASTM E501 [7] and RT3's siped Bridgestone Blizzak Nordic WN-01............. 13 2.11 Example of friction differences between tires measured with RT3 [1]............................... 14 2.12 Force distribution of a tire [4]................... 16 2.13 Tire deformation and rolling resistance............. 17 2.14 Longitudinal Slip-force curve on dry surface [5]......... 19 2.15 The slip curve varies with different surfaces [8]......... 20 2.16 Lateral force coefficient in relation to slip angle [5]....... 21 3.1 OSCAR [3]............................. 24 3.2 ROAR [3].............................. 25 3.3 Trelleborg T520 with straight grooves [9]............. 25 vii viii LIST OF FIGURES 3.4 Viafriction [3]............................ 26 3.5 Upper: transportation mode, lower: measurement mode [10].. 27 3.6 1: GEM-cell 2: Measurement wheel 3: Safety chain 4: center of rotation 5: sway bar 6: steering damper 7: shock absorber 8: transportation wheel [11].................... 28 3.7 Slip angle [11]............................ 29 4.1 Map over 1km measurement................... 32 4.2 Road conditions on Fv 541.................... 33 4.3 Long drive, RoAR 1....................... 34 4.4 5 km drive on Fv31........................ 34 4.5 Road preparation with "Fixed-sand" .............. 35 5.1 ROAR text-file structure..................... 38 5.2 ROAR parameter structure in Matlab.............. 38 5.3 Sample frequency difference................... 39 6.1 Unmodified- and modified RT3 data............... 44 6.2 Friction values from RT3 for all runs on Fv541 in lane 1... 45 6.3 Friction values from OSCAR for all runs on Fv541 in lane 1. 46 6.4 Difference distribution for RT3 vs. OSCAR for all runs on Fv541 in lane 1.......................... 47 6.5 RT3 and OSCAR plotted vs. distance, run 1 on Fv541 in lane 1 48 6.6 Friction values from ROAR 1 for all runs on Fv541 in lane 1. 48 6.7 Difference distribution from RT3 vs. RoAR 1 for all runs on Fv541 in lane 1.......................... 49 6.8 Box plot of the difference of each NPRA system and run vs. RT3 on Fv541 in lane 1...................... 50 6.9 Friction values from RT3 for all runs on Fv31 in lane 1.... 51 6.10 Friction values from ROAR 3 for all runs on Fv31 in lane 1.. 52 6.11 Difference distribution for RT3 vs. ROAR 3 for all runs on Fv31 in lane 1........................... 53 6.12 Friction values from ROAR 5 for all runs on Fv31 in lane 1.. 54 LIST OF FIGURES ix 6.13 Difference distribution for RT3 vs. ROAR 5 for all runs on Fv31 in lane 1........................... 55 6.14 Friction values from RT3, ROAR 3 & 5, first run on Fv31 in lane 1............................... 56 6.15 ROAR as a function of RT3 for two sets of measurements with regression line........................... 59 A.1 Friction values from the unmodified RT3 for all runs on Fv541 in lane 1.............................. 69 A.2 Friction values from ROAR 2 for all runs on Fv541 in lane 1. 70 A.3 Difference distribution from RT3 vs. ROAR 2 for all runs on Fv541 in lane 1.......................... 71 A.4 Friction values from ROAR 4 for all runs on Fv541 in lane 1. 72 A.5 Difference distribution from RT3 vs. ROAR 4 for all runs on Fv541 in lane 1.......................... 73 A.6 Friction values from ViaFriction for all runs on Fv541 in lane 1 73 A.7 Difference distribution from RT3 vs. ROAR 4 for all runs on Fv541 in lane 1.......................... 74 A.8 Friction values from the modified RT3 for all runs on Fv541 in lane 2.............................. 75 A.9 Friction values from OSCAR for all runs on Fv541 in lane 2. 76 A.10 Difference distribution from RT3 vs. OSCAR for all runs on Fv541 in lane 2.......................... 77 A.11 Friction values from ROAR 1 for all runs on Fv541 in lane 2. 77 A.12 Difference distribution from RT3 vs. ROAR 1 for all runs on Fv541 in lane 2.......................... 78 A.13 Friction values from the unmodified RT3 for all runs on Fv541 in lane 2.............................. 79 A.14 Friction values from ROAR 2 for all runs on Fv541 in lane 2. 80 A.15 Difference distribution from RT3 vs. ROAR 2 for all runs on Fv541 in lane 2.......................... 81 A.16 Friction values from ROAR 4 for all runs on Fv541 in lane 2. 81 x LIST OF FIGURES A.17 Difference distribution from RT3 vs. ROAR 2 for all runs on Fv541 in lane 2.......................... 82 A.18 Friction values from ViaFriction for all runs on Fv541 in lane 2 83 A.19 Difference distribution from RT3 vs. ROAR 2 for all runs on Fv541 in lane 2.......................... 84 A.20 Friction values from RT3 for all runs on Fv31 in lane 2.... 85 A.21 Friction values from ROAR 3 for all runs on Fv31 in lane 2.. 86 A.22 Difference distribution from RT3 vs. ROAR 3 for all runs on Fv31 in lane 2........................... 87 A.23 Friction values from ROAR 5 for all runs on Fv31 in lane 2.. 87 A.24 Difference distribution from RT3 vs. ROAR 3 for all runs on Fv31 in lane 2..........................