Search

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]

This study examines surface roughness measurements via piezo acoustic disks and appropriate signal processing. Surface roughness is one characteristic of surface texture that can have various irregularities inherent to manufacturing methods. The surface roughness parameters and corresponding surface profiles are acquired by a stylus profilometer. Simultaneously, elastic waves propagated along metal surfaces caused by the friction of a diamond tip are obtained in the form of raw sound via piezo acoustic disks. Frequency spectrum analysis showed apparent correlations between the traditionally obtained measurement parameters and the piezo acoustic measurement data. Thus, it is concluded that acoustic friction measurement shows promising results as a novel measurement method for the surface roughness states of certain materials. [ABSTRACT FROM AUTHOR]

Featured Application: The magic formula (MF) is used to estimate the road friction characteristics. This study deals with the possibility of construction of a database on the braking friction coefficient for actual roads from the viewpoint of traffic safety, especially for automated driving, such as level 4 or higher. At these levels of automated driving, the controller needs to control the vehicle. However, the road surface condition, especially the road friction coefficient on wet roads and snowy or icy roads, changes greatly, and in some cases, changes by almost one order. Therefore, it is necessary for the controller to constantly collect environment information, such as the road friction coefficients, and prepare for emergencies, such as obstacle avoidance. However, at present, the measurement of the road friction coefficients is not systemically performed, and a method for accurately measuring has not been established. In order to improve this situation, this study examines a method for continuous measurement of the road friction characteristics, such as the μ-s characteristics. It is shown that the μ-s characteristics are continuously measured using the MF generally used in tire engineering, and the friction characteristics identified from the results are sufficiently satisfactory. [ABSTRACT FROM AUTHOR]

Accurate friction-slip modelling is particularly important for locomotive traction and rail damage studies. This paper compares friction-slip measurement results from a hand operated (HO) tribometer and a twin disc tribomachine on AS60 rail. The results were used to calibrate traction coefficient-slip curves using the Modified Fastsim contact model. The differences between the two friction measuring instruments including scale, speed, and rail cleaning effect influenced the friction coefficient and slip value at which the friction peak occurred. The proposed equalisation technique was able to match the HO tribometer traction coefficient-slip curve with the tribomachine curve while preserving most of the Modified Fastsim contact parameters. • Friction-slip behaviour is characterised for locomotive traction and rail damage. • Friction measurements using tribomachine and hand-operated tribometer are compared. • Tribomachine and hand-operated tribometer results implemented in Modified Fastsim. [ABSTRACT FROM AUTHOR]

Measuring friction on the human body is challenging on areas where the surface of the skin is curved. Handheld devices for measuring friction may make it easier to rapidly measure from hard-to-reach areas, however, the orientation of the probe relative to the surface is often sub-optimal to reliably measure the normal force. Here, the friction on the surfaces of a mannequin and a human body are measured and corrected using a curvature correction technique. This is accomplished by accounting for the shape of the measurement surface and the orientation of the measurement device relative to that surface. Two strategies for constructing the surface shape of the measurement surface are compared. [Display omitted] • Implement a curved surface correction method in 3D with a linear sliding handheld tribometer. • Test methods for capturing the 3D curved surface shape for the surface correction method. • Measure sliding friction on a human body. [ABSTRACT FROM AUTHOR]

In situ measurement of frictional properties, particularly of human skin, is challenging. A major challenge is that the measured surface may be curved and oriented arbitrarily relative to the measurement device, making it difficult to obtain accurate and reliable friction estimates. Here we propose a method to simultaneously estimate the orientation of the surface during friction measurements, using a custom-made hand-held tribometer. The method accounts for the position and orientation of the tribometer relative to the shape of the measured surface. Our simple calibration method allows lightweight tribometers to be built with cheaper materials like plastic, without sacrificing accuracy. [Display omitted] • Propose a general method to measure force data on curved surfaces for sliding contacts and friction analysis. • Implement this curve correction method with a linear sliding handheld tribometer. • Describe the importance of carefully testing and calibrating the outputs of lightweight devices that may have low flexural rigidity. [ABSTRACT FROM AUTHOR]