Measurement of road friction coefficient using strain on tire sidewall.

If road friction coefficients can be measured in real time, the performance of advanced driver-assistance systems (ADASs), such as anti-lock braking systems (ABS) and automatic braking systems, can be improved. Generally, ADASs use information obtained from wheel speed sensors and acceleration sensors. However, it is difficult to accurately measure the road friction coefficients using these sensors. Therefore, many studies have been conducted to measure road friction coefficients using strains at the inside surface of a tire tread, which are the only places that ground road surfaces. However, sensors installed on the inside surface of a tire tread, where significant deformation occurs locally because of protrusions on road surfaces, can easily be peeled off or damaged. Therefore, this study investigated a method for measuring road friction coefficients using strains on the sidewalls of the tires. If the sidewalls of tires are used instead, stable measurements can be expected because the sidewalls of tires are harder to deform locally compared with the inside surface of a tire tread. First, using an experimental device that simulates the complete slip state of a tire, we measured the relationship between the triaxial direction loads acting on the ground surface of the tire and the strain induced on the sidewall of the tire. Subsequently, we established experimental formulas that express the relationship and devised methods for measuring the road friction coefficient. It was confirmed that the friction coefficients of multiple friction surfaces, even under triaxial direction loads, could be accurately measured using the proposed method. In conclusion, the proposed method was confirmed to be able to measure the load acting on a tire and friction coefficient of the tire grounding surface at low speeds and under full-slip conditions. • We proposed a measurement method for road friction coefficient by using strains on a tire sidewall. • The strain on the sidewall is confirmed to vary almost linearly concerning three-axis loads acting on a tire. • Three-axis loads and road friction coefficient can be obtained from sidewall-strain at three different tire rotation angles. [ABSTRACT FROM AUTHOR]