Performance validation of printed strain sensors for active control of intelligent tires

To ensure safety and comfort, the automotive industry employs sensors to monitor the vehicle dynamics, with growing interest in intelligent tires. This paper specifically presents the design and validation of a dynamic load sensor proposed for integration in tires to allow active control of noise inside the cabin of the car. The concept of using tire surface strain measurement is first experimentally investigated using a quarter-car test bench, through coherence evaluation between the vertical force injected at the wheel hub and the out-of-plane velocity field over the lateral surface of the tire, as measured using a scanning laser Doppler vibrometer (LDV). The tire sidewall deformations are found to correlate well with vertical road excitations, suggesting that strain measurement on the tires could a useful signal for noise control. Specifications are then established for a sensor to measure strain on the tire, leading to the design and fabrication of a Capacitive Strain Transducer (CST) using printed electrodes on a flexible substrate. A number of CSTs are bonded on the tire and characterized to determine optimal sensor locations. The coherence achieved between the CST measurements and the excitation force is compared with a reference Macro Fiber Composite (MFC) transducer. The CST shows promise for providing the reference signal required in feedforward algorithms for active noise and vibration control inside the car, since it shows good coherence with the force reference signal, but only for relatively large loads.