Optical sensors up-to-speed.

Oxford Brookes Formula Student team used a Correvit® S-Motion 2 Axis Optical Sensor from Kistler Instruments to obtain the key data needed for accurate, real world tyre modelling.

The Oxford Brookes University, 5 times winner of the British Formula Student competition, decided that better tyre modelling was essential for their 2018 campaign than that provided by data from a sandpaper belt test rig courtesy of the Formula SAE Tire Test Consortium. The team decided that real world data would be needed to support future development of the Oxford Brookes Formula Student car. Tyre slip angle, the key data needed for accurate tyre modelling, was obtained using a Correvit® S-Motion 2 Axis Optical Sensor on loan from Kistler Instruments.

As tyre modelling lead, Brad Mallinson, explains, “While vertical load, inclination angle, ride heights, and vehicle roll angle are relatively easily measured, tyre slip angle is very difficult but critical to the development of an accurate tyre model. Kistler’s S-Motion sensor accurately measures vehicle longitudinal and transverse speed and slip angle with a high logging rate which is essential for the relatively low-speed Formula Student driving events.”

The S-Motion unit was mounted on the 2017 Oxford Brookes Formula Student car, along with load cells, infrared tyre temperature and laser ride height sensors to collect as much tyre data as possible. A major benefit of the S-Motion system is the time saving “Plug & Play” capability which drastically reduces vehicle preparation time; essential to take full advantage of the short time frame for tyre testing after the Formula Student season. A further advantage of the Correvit® system is the ability to automatically transform speed and slip angle measurements to any point of interest on the vehicle. These were transformed to the centre of gravity where yaw rate was measured, simplifying tyre slip angle calculation during steady-state tests.

Testing consisted of increasing velocity runs on a constant radius skid pad for a minimum of three cold inflation pressures and three static camber settings to capture the quadratic relationships in the lateral force model. Quantities derived from measurements were calculated in MATLAB before being passed to the tyre model tool. Roll angle measurements from the S-Motion and damper displacement data were used for lateral weight transfer models to determine inclination angle and total vertical load. Steered angle of each front wheel was used to calculate front tyre slip angles using vehicle slip angle from the S-Motion.

Like the Oxford Brookes Formula Student Team, many automotive manufacturers are now using the Correvit® S-Motion and other sensors by Kistler to generate data for tyre models that represent real world tyre performance.

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