On a road tire deformation measurement system using a capacitive-resistive sensor

This paper presents a novel approach to continuously measure the mechanical deformations of a tire due to contact with asphalt, by embedding capacitive-resistive sensors in it. A strain monitoring method is proposed, which adopts the tire itself as a sensing element. In this way, the sensing area is pushed towards the tread interface ( the part of the tire in direct contact with the asphalt), where the information concerning tire state is actually generated. Tire deformation causes a change of the spacing between the steel wires inside the tire carcass and this change is translated into an impedance change of that region of the tire. By measuring such an impedance change, our approach makes it possible to determine the deformation of the tire. Static stress-strain measurements show a linearity of about 80% in the impedance-strain relation. A linear impulse of tensile strain has been used to validate the detection of instantaneous changes in the tread-asphalt interface. The mechanical solicitation resulted in a 1% deformation of the specimen's main dimension. Experimental results report a change of about 40% in the real part of the impedance and a change of about 20% in the imaginary part of the impedance. The same measurements have been performed varying the temperature within a range of -20 to 90 degrees C, which is compatible with the operating conditions of a commercial car tire.