A Measuring System for Continuous Friction Monitoring on Wet Track Surfaces

To improve and better understand the tire wet grip mechanism, it is essential to perform test bench measurements under wet conditions. On both public streets and the track surfaces of the internal drum test bench of the Karlsruhe Institute of Technology (KIT), a drop in the friction level of the track surface can be observed with an increasing number of wet measurements. For this purpose, a new measuring device was developed and built: the continuous friction monitoring system (CFM-System). The measuring principle is a continuously braked standard test tire, whereby a longitudinal friction coefficient is determined. To establish a suitable measuring method using the CFM-System, a basic understanding of the longitudinal behavior of this standard test tire was achieved. For this purpose, μ-slip characteristics were determined to investigate the friction behavior of this tire under different slip conditions. Furthermore, the influence of wheel load and driving speed were examined and analyzed. Based on these findings, an adequate test method was derived. The investigations presented in this article show a good relation between the results of the CFM-System and the results obtained from measurements using the standard reference test tire (SRTT). The results show that this new CFM-System is suitable for monitoring the grip level of the track surface on the internal drum test bench when performing wet grip measurements. It is assumed that the results can be directly transferred to the real road or to proving grounds because real track surfaces are used on the test bench.