Browsing by Author "Do, Minh-Tan"

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    Influence of Thin Waterfilm on Skid Resistance
    Beautru, Yannick; Cerezo, Veronique; Do, Minh-Tan; Kane, Malal (2012)
    Most of past research on the skid resistance/road wetness relationship deal with thick water depths (> 1mm). Questions remain as to the variation of skid resistance with thin water films and the transition between the dry state and the so-called “damp” or “humid” state at which the skid resistance drop can be as high as 30-40%. This paper deals with a theoretical and experimental assessment of the friction/water depth relationship. The main objective is to estimate local water depths trapped between the tire and the road asperities and to define a so-called “critical” water depth which can be used for driver assistance systems. Tests are performed in laboratory and on test tracks. It was found that the friction-water depth curves have an inverse-S shape and present an initial constant-friction part before decreasing to a minimum value. A “critical” water depth, defined as the water depth above which the friction coefficient collapses significantly, is determined from observed friction-water depth curves. Influence of test speed and road surface texture on critical water depth is discussed.
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    On-Board Estimation of Water Depth Using Low-Cost Sensors
    Prevost, Delphine; Cerezo, Veronique; Do, Minh-Tan; Chabanon, Christian (2012)
    Last century has seen the emergence of many active safety systems, which have highly participated in reducing the number of car crashes. Nevertheless, those systems can be improved. In particular, information about the wetness of pavement surface could be of high importance to evaluate real tire/road friction. This paper deals with a new way to estimate local water depths under the tires as the car is running. A direct measurement of the amount of water droplets thrown from rotating tires of the vehicle is used. Tests are performed on test tracks with a real passenger car equipped to estimate spray and splash of water created by the front right tire of the car. Different water depths are obtained by flooding test tracks then measuring while they are drying. An indicator linked to the amount of water droplets is defined and studied under different conditions. Effects of traveling speed, road texture or tire tread pattern are assessed. The relationship between the indicator and actual water depth is verified by using non-contact optical water depth sensors as a reference. This new method of measurement via water droplets is a major breakthrough in automotive engineering since low-cost sensors can be used to estimate the water depth.