Tire Splash and Spray Directly before and during Hydroplaning
Wet roads can have a serious impact on tire traction. There are several ways of detecting wet roads; however, almost all of them come with disadvantages. Using the splash and spray behavior of the tire can offer a solution. To identify key parameters that influence splash and spray, we used high-speed cameras to record tires rolling on an internal drum tire test bench. The key parameters were water film thickness, speed, and profile geometry (tread pattern and tread depth). Our image-processing analysis showed three main effects in the splash and spray behavior that help to characterize the water film thickness: side splash, circumferential spray, and torrent spray. Circumferential spray and torrent spray can be used to estimate low and medium water film thicknesses, but these require information about speed and profile geometry. Side splash announces hydroplaning without the need for additional information.ABSTRACT
Spray model based on [17,25].
Tested tires (all 245/35R20). Top left: Tire 1, Michelin new. Top right: Tire 2, Michelin worn. Bottom left: Tire 3, Pirelli new. Bottom right: Tire 4, Pirelli half worn.
Inner drum test bench with four cameras (highlighted). Computer-aided design based on [23].
Camera views. Top left: Action camera top view. Top right: High-speed camera. Bottom left: Action camera front view. Bottom right: Action camera rear view.
Process of the single droplet detection by the algorithm after [24]. The direction of the arrow represents the processing order. From the two centers, the brighter adjacent pixels are assigned to a droplet. If the brightness of the pixels between two droplets does not fall below the brightness threshold that marks droplet borders, pixels are assigned to the droplet with the nearest center. Crosses mark pixels that would otherwise be claimed by two different droplets.
Top left: Raw picture. Top right: Same picture with highlighted droplets detected by the algorithm. Bottom left: Triangulation to assign real sizes to a pixel via correction factor. Bottom mid: Zones with the same correction factor. Bottom right: Zones from the same spray off angle.
Schematic depiction of the droplet detachment from edges and the center of the tread.
Relative droplet size over speed with two different water film thicknesses from tire 1.
Relative detachment frequency over speed and two different water film thicknesses from tire 1. Data points from 0.5-mm water film thickness at 120 and 140 kph are not valid.
Influence of tread pattern and tread depth on circumferential spray at a speed of 60 kph and a water film thickness of 0.6 mm. Top left: Tire 1. Top right: Tire 2. Bottom left: Tire 3. Bottom right: Tire 4.
Torrent spray behavior of tire 2. Top left: 40 kph, 0.3-mm water film thickness, no torrent spray. Top right: 40 kph, 0.5-mm water film thickness, some droplets detach in torrent spray. Bottom right: 120 kph, 0.5-mm water film thickness, two small jets visible, tire partly in hydroplaning. Bottom left: 120 kph, 1-mm water film thickness, two turbulent jets visible, tire in full hydroplaning.
Influence of wheel load and tire pressure on torrent spray (tire 3, 80 kph, 2-mm water film thickness). Top: Maximum wheel load (4800 N) and minimum tire pressure (1.7 bar). Bottom: Minimum wheel load (3800 N) and maximum tire pressure (2.7 bar).
Side splash behavior of tire 2. Top left: 50 kph, 0.5-mm water film thickness, no side splash visible. Top right: 60 kph, 1-mm water film thickness, side splash visible, but no hydroplaning. Bottom right: 60 kph, 2-mm water film thickness, hydroplaning. Bottom left: 70 kph, 1-mm water film thickness, hydroplaning.