Frankfurt am Main, Germany, April 12, 2018. Dry, icy, snowy, or wet: awareness of road conditions is a crucial safety factor as accidents in severe weather arise mainly due to significant loss of friction between tyres and the surface of the road. With its Road Condition Observer, Continental has introduced a solution that allows road conditions to be classified with regard to tyre/road friction. A specific situation called aquaplaning is extremely dangerous for manually driven vehicles as well as automated ones. Technology company Continental has now begun to develop new sensor-based concepts to warn the driver in the event of imminent loss of friction. When there is a thick layer of water on the road, the water pressure between the tyre footprint and the road surface can make the front wheels float. Braking and steering are no longer possible, and the driver loses control of the vehicle.
“Wet road conditions are difficult for a car driver to evaluate,” said Bernd Hartmann, head of Enhanced ADAS (Advanced Driver Assistance Systems) & Tyre Interactions within the Advanced Technology department of Continental’s Chassis & Safety division. “Once you feel your vehicle floating, it is too late. Our aquaplaning assistance concepts detect the early aquaplaning phase to make the driver aware of what is going on under the tyres. This can help drivers or automated vehicles to adapt their speed appropriately to wet road conditions.”
The system under development is all encompassing – tyres, tyre sensors, cameras, algorithms, brake actuation, and the human-machine interface.
Continental’s developers are focused on predicting and managing the risk of aquaplaning. The objective is to detect a possible front-wheel floating situation as early as possible in order to trigger an early warning to the driver. Utilising signals from surround view cameras and tyre-mounted eTIS (electronic-Tyre Information System) sensors, an early warning concerning the approaching aquaplaning situation is provided to the driver. Continental is also working on the control and stabilisation of vehicles in aquaplaning situations, such as torque vectoring by individual wheel braking.
Aquaplaning conditions can also occur unexpectedly with no opportunity for advance warning. In such cases, the potential risk to other vehicles on the road can be mitigated by early communication via V2X technology and eHorizon, facilitating a network of solidarity where one vehicle acts as a safety sensor for all other vehicles and not just those in its direct vicinity. eHorizon can provide this information to vehicles that could potentially be affected, so they are able to adjust their driving functions to the aquaplaning conditions.
To detect aquaplaning situations, video images from surround view cameras mounted in the side mirrors, the grill, and rear are analysed. “When there is a lot of water on the road, the camera images show a specific splash and spray pattern that can be detected as aquaplaning in its early phase”, explained Hartmann. For example, excessive water displacement in all directions underneath the tyre is a characteristic attribute. During the first testing phase of the new solution, the wetness recognition algorithms delivered a very high hit ratio in predicting potential aquaplaning conditions.
In addition to image information, Continental uses information from tyres to detect the risk of aquaplaning. In this concept, signals from Continental’s eTIS sensors, mounted on the tyre’s inner liner, are computed. “We use the accelerometer signal from the electronic-Tyre Information System to look for a specific signal pattern”, said Andreas Wolf, head of Continental's Body & Security business unit. A tyre model processes the incoming radial acceleration of the part of the tyre that is in contact with the road. For wet roads – when enough water is transported out of the tread to ensure an appropriate grip – the signal shows a distinct pattern. As soon as a wedge of water begins to form in front of the tyre footprint region and there is excessive water on the road, the acceleration signal begins to oscillate in a characteristic way, indicating an early risk of aquaplaning. Since the eTIS sensor can also detect the remaining depth of the tyre tread, a safe speed for a given wet road condition can be calculated and communicated to the driver.
Testing has shown that future aquaplaning assistance will also have the potential to intervene in an actual aquaplaning situation by applying the rear brakes in a controlled way to establish a degree of “torque vectoring” in order to maintain vehicle maneuverability within physical limits.
Not only is aquaplaning a challenge to the driver, but it is also difficult to pin down how many city road and highway accidents in wet road conditions are caused by floating front wheels. “This is one of the last blank spots on the strategic map towards greater road safety”, said Bernd Hartmann. But drivers must continue to consider a general rule: adjusting their speed to wet roads and keeping an eye on the tyre’s tread depth. Since aquaplaning depends on tread depth, the height of the water on the road and speed, Continental recommends renewing summer tyres with three millimeters of residual tread depth. Below this limit, the risk of aquaplaning increases significantly.